U.S. patent application number 16/036390 was filed with the patent office on 2019-08-01 for x-ray tube having planar emitter and magnetic focusing and steering components.
The applicant listed for this patent is VAREX IMAGING CORPORATION. Invention is credited to Bradley D. Canfield, Colton B. Woodman.
Application Number | 20190237286 16/036390 |
Document ID | / |
Family ID | 53005090 |
Filed Date | 2019-08-01 |
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United States Patent
Application |
20190237286 |
Kind Code |
A1 |
Canfield; Bradley D. ; et
al. |
August 1, 2019 |
X-RAY TUBE HAVING PLANAR EMITTER AND MAGNETIC FOCUSING AND STEERING
COMPONENTS
Abstract
An X-ray tube can include: a cathode including an electron
emitter that emits an electron beam; an anode configured to receive
the emitted electrons of the electron beam; a first magnetic
quadrupole between the cathode and the anode; a second magnetic
quadrupole between the first magnetic quadrupole and the anode; a
magnetic dipole between the cathode and anode; and a power supply
system operably coupled with the first magnetic quadrupole, second
magnetic quadrupole, and magnetic dipole, the power supply system
being configured to: produce a first focusing magnetic quadrupole
field at the first magnetic quadrupole; produce a second focusing
magnetic quadrupole field at the second magnetic quadrupole; and
produce a steering magnetic dipole field at the magnetic dipole
configured to deflect the electron beam in order to shift a focal
spot of the electron beam on the anode.
Inventors: |
Canfield; Bradley D.; (Orem,
UT) ; Woodman; Colton B.; (West Valley City,
UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VAREX IMAGING CORPORATION |
Salt Lake City |
UT |
US |
|
|
Family ID: |
53005090 |
Appl. No.: |
16/036390 |
Filed: |
July 16, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14660584 |
Mar 17, 2015 |
10026586 |
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16036390 |
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PCT/US2014/063015 |
Oct 29, 2014 |
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14660584 |
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14642283 |
Mar 9, 2015 |
10008359 |
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14660584 |
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61897181 |
Oct 29, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 35/305 20130101;
H05G 1/10 20130101; H05G 1/52 20130101; H01J 35/14 20130101; H01J
35/30 20130101; H01J 35/06 20130101 |
International
Class: |
H01J 35/14 20060101
H01J035/14; H01J 35/30 20060101 H01J035/30; H01J 35/06 20060101
H01J035/06; H05G 1/52 20060101 H05G001/52; H05G 1/10 20060101
H05G001/10 |
Claims
1. An X-ray tube comprising: a cathode including an electron
emitter that emits an electron beam; an anode configured to receive
the emitted electrons of the electron beam; a first magnetic
quadrupole between the cathode and the anode; a second magnetic
quadrupole between the first magnetic quadrupole and the anode; a
magnetic dipole between the cathode and anode; and a power supply
system operably coupled with the first magnetic quadrupole, second
magnetic quadrupole, and magnetic dipole, the power supply system
being configured to: produce a first focusing magnetic quadrupole
field at the first magnetic quadrupole; produce a second focusing
magnetic quadrupole field at the second magnetic quadrupole; and
produce a steering magnetic dipole field at the magnetic dipole
configured to deflect the electron beam in order to shift a focal
spot of the electron beam on the anode.
2. The X-ray tube of claim 1, wherein the first magnetic quadrupole
includes a first magnetic yoke, the second magnetic quadrupole
includes a second magnetic yoke, and the magnetic dipole includes
the first magnetic yoke or the second magnetic yoke.
3. The X-ray tube of claim 1, further comprising: the first
magnetic quadrupole being configured for providing a first magnetic
quadrupole gradient for focusing the electron beam in a first
direction and defocusing the electron beam in a second direction
orthogonal to the first direction; and the second magnetic
quadrupole being configured for providing a second magnetic
quadrupole gradient for focusing the electron beam in the second
direction and defocusing the electron beam in the first direction,
wherein a combination of the first and second magnetic quadrupoles
provides a net focusing effect in both first and second directions
of a focal spot of the electron beam.
4. The X-ray tube of claim 1, further comprising: the first
magnetic quadrupole being operably coupled with a first focus power
supply; the second magnetic quadrupole being operably coupled with
a second focus power supply; a first dipole pair of the magnetic
dipole being operably coupled with a first steering power supply;
and a second dipole pair of the magnetic dipole being operably
coupled with a second steering power supply.
5. The X-ray tube of claim 1, further comprising: the first
magnetic quadrupole being operably coupled with a first focus power
supply; the second magnetic quadrupole being operably coupled with
a second focus power supply; and the magnetic dipole including four
dipole electro magnets, each electromagnet of the magnetic dipole
being operably coupled with a different steering power supply.
6. The X-ray tube of claim 1, the magnetic dipole comprising two
magnetic dipoles that are orthogonal with respect to each other,
each of the two magnetic dipoles being configured to deflect the
electron beam in order to shift the focal spot of the electron beam
on the anode.
7. The X-ray tube of claim 1, the magnetic dipole comprising a pair
of magnetic dipoles being configured together to deflect the
electron beam in an first axis and/or second axis orthogonal with
the first axis in order to shift a focal spot of the electron beam
on the anode.
8. The X-ray tube of claim 1, further comprising: the first
magnetic quadrupole having a first quadrupole yoke with four first
quadrupole pole projections extending from the first quadrupole
yoke and oriented toward a central axis of the first quadrupole
yoke and each of the four first quadrupole pole projections having
a first quadrupole electromagnetic coil; and the second magnetic
quadrupole having a second quadrupole yoke with four second
quadrupole pole projections extending from the second quadrupole
yoke and oriented toward a central axis of the second quadrupole
yoke and each of the four second quadrupole pole projections having
a second quadrupole electromagnetic coil.
9. The X-ray tube of claim 8, further comprising: the magnetic
dipole having a dipole yoke with four dipole pole projections and
four dipole electromagnetic coils, wherein the first quadrupole
yoke, second quadrupole yoke, and dipole yoke are separate
yokes.
10. The X-ray tube of claim 9, further comprising: the four dipole
electromagnetic coils being wrapped around the dipole yoke in an
even distribution; or each dipole pole projection has a dipole
electromagnetic coil wrapped there around.
11. The X-ray tube of claim 9, comprising: the four first
quadrupole pole projections having the first quadrupole
electromagnetic coils being at 45, 135, 225, and 315 degrees; the
four second quadrupole pole projections having the second
quadrupole electromagnetic coils being at 45, 135, 225, and 315
degrees; and the four dipole pole projections and/or four dipole
electromagnetic coils being at: 0, 90, 180, and 270 degrees; or at
45, 135, 225, and 315 degrees.
12. The X-ray tube of claim 9, wherein the power supply system
comprises: a first focusing power supply operably coupled with the
four first quadrupole electromagnetic coils to produce the first
focusing magnetic quadrupole field; a second focusing power supply
operably coupled with the four second quadrupole electromagnetic
coils to produce the second focusing magnetic quadrupole field; a
first steering power supply operably coupled with at least one
first dipole coil and configured for steering the electron beam in
a first direction; and a second steering power supply operably
coupled with at least one second dipole coil and configured for
steering the electron beam in a second direction that is orthogonal
with the first direction, wherein the at least one first dipole
coil is different from the at least one second dipole coil.
13. The X-ray tube of claim 12, comprising two opposing first
dipole coils coupled in series to the first steering power supply
or to the second steering power supply of the power supply system
that provides an alternating current offset to the two opposing
dipole coils.
14. The X-ray tube of claim 12, comprising two pairs of opposing
dipole coils coupled to the power supply system that provides an
alternating current offset to the two pairs of opposing dipole
coils, a first pair of the two pairs of opposing dipole coils being
coupled with the first steering power supply and a second pair of
the two pairs of opposing dipole coils being coupled with the
second steering power supply.
15. The X-ray tube of claim 12, wherein the power supply system
further comprises: a command input controller; and a command
processor operably coupled with the command input controller to
receive command inputs therefrom, and operably coupled with the
first focusing power supply, second focusing power supply, first
steering power supply and second steering power supply to provide
the inputs thereto in order to control focusing and steering of the
electron beam.
16. The X-ray tube of claim 15, wherein: the command input
controller is configured for command inputs of: current, large
focal spot, small focal spot, voltage, and steering toggle pattern;
or the command processor is configured to determine: a first
current for focusing in a first axis, a second current for focusing
in a second axis that is orthogonal with the first axis, a first
wave form and amplitude for steering in a first direction, and a
second wave form and amplitude for steering in a second direction
orthogonal with the first direction.
17. The X-ray tube of claim 12, wherein: the first focusing power
supply is operably coupled with the four first quadrupole
electromagnetic coils in series; the second focusing power supply
is operably coupled with the four second quadrupole electromagnetic
coils in series; the first steering power supply is operably
coupled with two first dipole coils in series; and the second
steering power supply is operably coupled with two second dipole
coils in series.
18. A method of focusing and steering an electron beam in an X-ray
tube, the method comprising: providing the X-ray tube of claim 1;
operating the electron emitter so as to emit the electron beam from
the cathode to the anode along an electron beam axis; operating the
first magnetic quadrupole to focus the electron beam in a first
axis; operating the second magnetic quadrupole to focus the
electron beam in a second axis orthogonal with the first axis; and
operating the magnetic dipole with alternating current offset to
steer the electron beam away from the electron beam axis.
19. The method of claim 18, further comprising inputting command
inputs into a command input controller in order to control focusing
in the first axis, focusing in the second axis, and/or steering
away from the electron beam in a first direction and/or second
direction, wherein a command processor is operably coupled with the
command input controller to receive the command inputs therefrom,
and operably coupled with the first focusing power supply, second
focusing power supply, first steering power supply and second
steering power supply to provide the inputs thereto in order to
control focusing and steering of the electron beam.
20. The method of claim 19, comprising, in response to the command
inputs, the command processor determining: a first current for
focusing in a first axis; a second current for focusing in a second
axis that is orthogonal with the first axis; a first wave form and
amplitude for steering in a first direction; and a second wave form
and amplitude for steering in a second direction orthogonal with
the first direction.
21. An X-ray tube comprising: a cathode including an electron
emitter that emits an electron beam; an anode configured to receive
the emitted electrons of the electron beam; a first magnetic
quadrupole between the cathode and the anode; a second magnetic
quadrupole between the first magnetic quadrupole and the anode; a
magnetic dipole between the cathode and anode, wherein the first
magnetic quadrupole, second magnetic quadrupole, and magnetic
dipole are separate; and a power supply system operably coupled
with the first magnetic quadrupole, second magnetic quadrupole, and
magnetic dipole, the power supply system being configured to:
produce a first focusing magnetic quadrupole field at the first
magnetic quadrupole; produce a second focusing magnetic quadrupole
field at the second magnetic quadrupole; and produce a steering
magnetic dipole field at the magnetic dipole configured to deflect
the electron beam in order to shift a focal spot of the electron
beam on the anode.
22. The X-ray tube of claim 21, wherein the X-ray tube has: the
following order along the emitted electrons: cathode, first
magnetic quadrupole, second magnetic quadrupole, magnetic dipole,
and anode; or the magnetic dipole includes a dipole yoke with four
dipole electromagnetic coils.
Description
CROSS-REFERENCE
[0001] This patent application is a continuation of U.S. patent
application Ser. No. 14/660,584 filed Mar. 17, 2015, which is a
continuation-in-part application of PCT Patent Application Serial
No. PCT/US2014/063015 filed Oct. 29, 2014, which claims priority to
U.S. Provisional Application Ser. No. 61/897,181 filed Oct. 29,
2013, and U.S. patent application Ser. No. 14/660,584 filed Mar.
17, 2015 is a continuation-in-part of U.S. patent application Ser.
No. 14/642,283 filed Mar. 9, 2015, which patent applications are
incorporated herein by specific reference in its entirety.
BACKGROUND
[0002] X-ray tubes are used in a variety of industrial and medical
applications. For example, X-ray tubes are employed in medical
diagnostic examination, therapeutic radiology, semiconductor
fabrication, and material analysis. Regardless of the application,
most X-ray tubes operate in a similar fashion. X-rays, which are
high frequency electromagnetic radiation, are produced in X-ray
tubes by applying an electrical current to a cathode to cause
electrons to be emitted from the cathode by thermionic emission.
The electrons accelerate towards and then impinge upon an anode.
The distance between the cathode and the anode is generally known
as A-C spacing or throw distance. When the electrons impinge upon
the anode, the electrons can collide with the anode to produce
X-rays. The area on the anode in which the electrons collide is
generally known as a focal spot.
[0003] X-rays can be produced through at least two mechanisms that
can occur during the collision of the electrons with the anode. A
first X-ray producing mechanism is referred to as X-ray
fluorescence or characteristic X-ray generation. X-ray fluorescence
occurs when an electron colliding with the material of the anode
has sufficient energy to knock an orbital electron of the anode out
of an inner electron shell. Other electrons of the anode in outer
electron shells fill the vacancy left in the inner electron shell.
As a result of the electron of the anode moving from the outer
electron shell to the inner electron shell, X-rays of a particular
frequency are produced. A second X-ray producing mechanism is
referred to as Bremsstrahlung. In Bremsstrahlung, electrons emitted
from the cathode decelerate when deflected by nuclei of the anode.
The decelerating electrons lose kinetic energy and thereby produce
X-rays. The X-rays produced in Bremsstrahlung have a spectrum of
frequencies. The X-rays produced through either Bremsstrahlung or
X-ray fluorescence may then exit the X-ray tube to be utilized in
one or more of the above-mentioned applications.
[0004] In certain applications, it may be beneficial to lengthen
the throw length of an X-ray tube. The throw length is the distance
from the cathode electron emitter to the anode surface. For
example, a long throw length may result in decreased back ion
bombardment and evaporation of anode materials back onto the
cathode. While X-ray tubes with long throw lengths may be
beneficial in certain applications, a long throw length can also
present difficulties. For example, as a throw length is lengthened,
the electrons that accelerate towards an anode through the throw
length tend to become less laminar resulting in an unacceptable
focal spot on the anode. Also affected is the ability to properly
focus and/or position the electron beam towards the anode target,
again resulting in a less than desirable focal spot--either in
terms of size, shape and/or position. When a focal spot is
unacceptable, it may be difficult to produce useful X-ray
images.
[0005] The subject matter claimed herein is not limited to
embodiments that solve any disadvantages or that operate only in
environments such as those described above. Rather, this background
is only provided to illustrate one exemplary technology area where
some embodiments described herein may be practiced.
SUMMARY
[0006] Disclosed embodiments address these and other problems by
improving X-ray image quality via improved electron emission
characteristics, and/or by providing improved control of a focal
spot size and position on an anode target. This helps to increase
spatial resolution or to reduce artifacts in resulting images.
[0007] In one embodiment, an electron emitter can include: a
plurality of elongate rungs connected together end to end from a
first emitter end to a second emitter end in a plane so as to form
a planar pattern, each elongate rung having a rung width dimension;
a plurality of corners, wherein each elongate rung is connected to
another elongate rung through a corner of the plurality of corners,
each corner having a corner apex and an opposite corner nadir
between the connected elongate rungs of the plurality of elongate
rungs; a first gap between adjacent non-connected elongate rungs of
the plurality of elongate rungs, wherein the first gap extends from
the first emitter end to a middle rung; a second gap between
adjacent non-connected elongate rungs of the plurality of elongate
rungs, wherein the second gap extends from the second emitter end
to the middle rung, wherein the first gap does not intersect the
second gap; and one or more cutouts at one or more of the corners
of the plurality of corners between the corner apex and corner
nadir or at the corner nadir.
[0008] In one embodiment, a method of designing an electron emitter
can include: determining a desired cross-sectional profile of an
electron emission from an electron emitter, where the parameters of
the electron emitter can be input into a computer; determining a
desired temperature profile for the electron emitter that emits the
desired cross-sectional profile; and determining desired emitter
dimensions for a defined electrical current through the electron
emitter that produces the desired temperature profile, which can be
determined through simulations run on the computer under
instructions input by the user. The emitter dimensions can include:
each rung width dimension; each first gap segment dimension; each
second gap segment dimension; and each web dimension. The electron
emitter can include: a plurality of elongate rungs connected
together end to end at corners, each corner having a corner apex
and an opposite corner nadir, each elongate rung having a rung
width dimension; a first gap between adjacent non-connected
elongate rungs from the first emitter end to a middle rung, the
first gap including a plurality of first gap segments each having a
first gap segment width; a second gap between adjacent
non-connected elongate rungs from the second emitter end to the
middle rung, the second gap including a plurality of second gap
segments each having a second gap segment width; and one or more
body portions of each corner between the corner apex and corner
nadir together define a web dimension for each corner.
[0009] In one embodiment, a method of manufacturing an electron
emitter can include: obtaining a sheet of electron emitter
material; obtaining an electron emitter pattern; and laser cutting
the electron emitter pattern into the electron emitter material.
The electron emitter pattern can include: a plurality of elongate
rungs connected together end to end from a first emitter end to a
second emitter end in a plane so as to form a planar pattern, each
elongate rung having a rung width dimension; a plurality of
corners, wherein each elongate rung is connected to another
elongate rung through a corner of the plurality of corners, each
corner having a corner apex and an opposite corner nadir between
the connected elongate rungs of the plurality of elongate rungs; a
first gap between adjacent non-connected elongate rungs of the
plurality of elongate rungs, wherein the first gap extends from the
first emitter end to a middle rung; a second gap between adjacent
non-connected elongate rungs of the plurality of elongate rungs,
wherein the second gap extends from the second emitter end to the
middle rung, wherein the first gap does not intersect the second
gap; and one or more cutouts at one or more of the corners of the
plurality of corners between the corner apex and corner nadir or at
the corner nadir. In one aspect, the method can further include
determining that the electron emitter pattern produces a desired
temperature profile for a defined electrical current.
[0010] In one embodiment, an X-ray tube can include: a cathode
including an electron emitter that emits an electron beam; an anode
configured to receive the emitted electrons of the electron beam; a
first magnetic quadrupole core between the cathode and the anode
and having a first quadrupole yoke with four evenly distributed
first quadrupole pole projections extending from the first
quadrupole yoke and oriented toward a central axis of the first
quadrupole yoke and each of the four first quadrupole pole
projections having a first quadrupole electromagnetic coil operably
coupled to a power supply system that provides a constant current
to each first quadrupole electromagnetic coil to produce a first
focusing magnetic quadrupole field; a second magnetic quadrupole
core between the first magnetic quadrupole and the anode and having
a second quadrupole yoke with four evenly distributed second
quadrupole pole projections extending from the second quadrupole
yoke and oriented toward a central axis of the second quadrupole
yoke and each of the four second quadrupole pole projections having
a second quadrupole electromagnetic coil operably coupled to the
power supply system that provides a constant current to each second
quadrupole electromagnetic coil to produce a second focusing
quadrupole field; and at least one coil of a pair of opposing
quadrupole electromagnetic coils of the first or second quadrupole
electromagnetic coils operably coupled to the power supply system
that provides an alternating current offset to at least one coil of
the pair of opposing quadrupole electromagnetic coils to shift the
first and/or second focusing quadrupole field from the central axis
of the first and/or second quadrupole yokes. In one aspect, the
X-ray tube can include two coils of a pair or two pairs of opposing
quadrupole electromagnetic coils of the first and/or second
quadrupole electromagnetic coils, which pair of coils include at
least one coil and optionally two coils operably coupled to the
power supply system that provides an alternating current offset
(e.g., AC offset) to one or both coils of one or two pairs of
opposing quadrupole electromagnetic coils to shift the first and/or
second focusing quadrupole field from the central axis of the first
and/or second quadrupole yokes.
[0011] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing an X-ray tube
of one of the embodiments (e.g., having at least one coil of a pair
of opposing quadrupole electromagnetic coils with constant current
for focusing and AC offset for steering); operating the electron
emitter so as to emit the electron beam from the cathode to the
anode along an electron beam axis; operating the first magnetic
quadrupole to focus the electron beam in a first direction;
operating the second magnetic quadrupole to focus the electron beam
in a second direction orthogonal with the first direction; and
operating a power supply to provide an AC offset to at least one
coil of a pair of opposing quadrupole electromagnetic coils so as
to steer the electron beam away from the electron beam axis. In one
aspect, the method can include operating two orthogonal pair of
opposing quadrupole electromagnetic coils by providing AC offset to
at least one coil of each pair so as to steer the electron beam
away from the electron beam axis. In one aspect, the opposing
quadrupole magnetic coils of a coil pair can be operated
independently (e.g., one coil with offset the other coil without
offset or at a different offset) so as to perturb the quadrupole
field and move the center of the quadrupole field away from the
central axis, thereby moving the electron beam away from the
central axis.
[0012] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing the X-ray
tube of one of the embodiments; operating the electron emitter so
as to emit the electron beam from the cathode to the anode along an
electron beam axis; operating the first magnetic quadrupole to
focus the electron beam in a first direction; operating the second
magnetic quadrupole to focus the electron beam in a second
direction orthogonal with the first direction; offsetting the first
magnetic quadrupole to steer the electron beam away from the
electron beam axis in a first direction; and offsetting the second
magnetic quadrupole to steer the electron beam away from the
electron beam axis in a second direction that is orthogonal to the
first direction.
[0013] In one embodiment, an X-ray tube can include: a cathode
including an electron emitter that emits an electron beam; an anode
configured to receive the emitted electrons of the electron beam; a
first magnetic quadrupole between the cathode and the anode and
having a first quadrupole yoke with four evenly distributed first
quadrupole pole projections extending from the first quadrupole
yoke and oriented toward a central axis of the first quadrupole
yoke and each of the four first quadrupole pole projections having
a first quadrupole electromagnetic coil; a second magnetic
quadrupole between the first magnetic quadrupole and the anode and
having a second quadrupole yoke with four evenly distributed second
quadrupole pole projections extending from the second quadrupole
yoke and oriented toward a central axis of the second quadrupole
yoke and each of the four second quadrupole pole projections having
a second quadrupole electromagnetic coil; and two opposing pole
projections of the first or second quadrupole pole projections
having electromagnetic steering coils formed thereof. That is, the
steering coils are collocated on the same pole projections that
include quadrupole coils. The steering coils produce an offset
quadrupole field by one steering coil or a pair of steering coils
having an AC offset that perturbs the quadrupole field that is
generated by the quadrupole electromagnetic coils, which shifts the
center of the quadrupole field from a central axis (e.g., electron
beam axis, center of cores, center of X-ray tube, etc.). The
shifted quadrupole field steers the electron beam passing
therethrough. The electromagnetic steering coils can be formed
adjacent to quadrupole electromagnetic coils of the first or second
quadrupole electromagnetic coils. In one aspect, the X-ray tube can
include one steering coil, one pair of steering coils, three
steering coils, or two pairs of steering coils. Each of the pairs
of steering coils having steering coils on opposing pole
projections of the first and/or second quadrupole pole projections.
Accordingly, a first single steering coil or first pair of steering
coils can shift the quadrupole field in a first direction, and a
second single coil or second pair of steering coils can shift the
quadrupole in a second direction that is orthogonal with the first
direction.
[0014] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing an X-ray tube
of one of the embodiments (e.g., having at least one steering coil
or one pair of steering coils on opposing quadrupole pole
projections); operating the electron emitter so as to emit the
electron beam from the cathode to the anode along an electron beam
axis; operating the first magnetic quadrupole to focus the electron
beam in a first direction; operating the second magnetic quadrupole
to focus the electron beam in a second direction orthogonal with
the first direction; and operating at least one steering coil or
the pair of steering coils to steer the electron beam away from the
center of the quadrupole cores or away from the natural electron
beam axis (e.g., without steering) that is aligned with the center
axis of the X-ray tube. In one aspect, the method can include
operating at least one coil of opposing steering coils to have
different currents to form an asymmetric quadrupole moment. That
is, each steering coil of a pair can be operated at different
currents to form and move an asymmetric quadrupole field in one
direction. Also, each steering coil of each pair (e.g., all four
steering coils) can be operated at different currents to form and
move an asymmetric quadrupole field in two orthogonal directions.
Operating one or two pairs of steering coils can shift the
quadrupole field off axis to steer the electron beam. However, only
one steering coil of each pair needs to be provided with AC offset
for steering the electron beam. Activating one coil with AC offset
can be considered to be operating the pair of opposing coils that
has that one coil with AC offset because the other coil of the pair
can have zero AC offset.
[0015] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing the X-ray
tube of one of the embodiments (e.g., having at least two pairs of
steering coils on two pairs of quadrupole pole projections);
operating the electron emitter so as to emit the electron beam from
the cathode to the anode along an electron beam axis; operating the
first magnetic quadrupole to focus the electron beam in a first
direction; operating the second magnetic quadrupole to focus the
electron beam in a second direction orthogonal with the first
direction; operating at least one coil of a first pair of steering
coils on an opposing pair of quadrupole pole projections to steer
the electron beam away from the electron beam axis in a first
direction; and operating at least one coil of a second pair of
steering coils on a pair of opposing quadrupole pole projections to
steer the electron beam away from the electron beam axis in a
second direction that is orthogonal to the first direction. In one
aspect, the method can include operating opposing steering coils to
have different powers to form a first asymmetric quadrupole moment.
In one aspect, the method can include operating two pair of
opposing steering coils so that each steering coil (e.g., all four
steering coils) has a different current from the other coils so as
to form a first asymmetric quadrupole moment. In one aspect, the
method can include operating opposing steering coils of a second
pair of steering coils to have different currents to form a second
asymmetric quadrupole moment.
[0016] In one embodiment, one quadrupole (e.g., of a quadrupole
core) is used to focus in the first direction and the second
quadrupole (e.g., of a quadrupole core) to focus in the second
direction and a dipole (e.g., of a dipole core) is used to steer in
one or both directions. Additionally, the dipole core can be
configured for two axis beam steering. In one aspect, the dipole
core can be configured for high dynamic response. This provides
three separate cores, one for focusing in the width (e.g., 1.sup.st
quadrupole core), one for focusing in the length (e.g., 2.sup.nd
quadrupole core), and one for beam steering (e.g., dipole core).
The dipole core can be operated similarly to the embodiment having
the steering coils, where the dipole coils can be steering coils,
or similarly to embodiments where the quadrupole coils have AC
offset, where the dipole coils are operated with AC offset.
[0017] In yet another embodiment, an electron source is provided in
the form of an electron emitter, such as a flat emitter, for the
production of electrons. The emitter has a relatively large
emitting area with design features that can be tuned to produce the
desired distribution of electrons to form a primarily laminar beam.
The emission over the emitter surface is not uniform or homogenous;
it is focused and steered with the quadrupole and dipole cores to
meet the needs of a given application. As the beam flows from the
cathode to the anode, the electron density of the beam spreads the
beam apart significantly during transit. The increased beam current
levels created by higher power requirements exacerbate the
spreading of the beam during transit. In disclosed embodiments, to
achieve the focal spot sizes required, the beam is focused by two
quadrupoles and then steered by the two dipoles as it transits from
the cathode to the anode. This also provides for creating a
multiplicity of sizes from a single emitter; the size conceivably
could be changed during an exam as well. This allows for the focal
spot to be changed on the fly. The increased emitter area of the
flat and planar geometry of the emitter allows production of
sufficient electrons flowing laminarly to meet the power
requirements. To address the requirement of steering the beam in
two dimensions so as to provide the desired imaging enhancements, a
pair of magnetic dipoles is used to deflect the beam to the desired
positions at the desired time. One dipole pair set is provided for
each direction.
[0018] The foregoing summary is illustrative only and is not
intended to be in any way limiting. In addition to the illustrative
aspects, embodiments, and features described above, further
aspects, embodiments, and features will become apparent by
reference to the drawings and the following detailed
description.
BRIEF DESCRIPTION OF THE FIGURES
[0019] The foregoing and following information as well as other
features of this disclosure will become more fully apparent from
the following description and appended claims, taken in conjunction
with the accompanying drawings. Understanding that these drawings
depict only several embodiments in accordance with the disclosure
and are, therefore, not to be considered limiting of its scope, the
disclosure will be described with additional specificity and detail
through use of the accompanying drawings.
[0020] FIG. 1A is a perspective view of an example X-ray tube in
which one or more embodiments described herein may be
implemented.
[0021] FIG. 1B is a side view of the X-ray tube of FIG. 1A.
[0022] FIG. 1C is a cross-sectional view of the X-ray tube of FIG.
1A.
[0023] FIG. 1D is a perspective view of internal components of an
embodiment of an example X-ray tube.
[0024] FIG. 2A is a perspective view of an embodiment of a cathode
head and planar electron emitter.
[0025] FIG. 2B is a perspective view of an embodiment of an
internal region of the cathode head that shows electrical leads for
the planar electron emitter of FIG. 2A.
[0026] FIG. 2C is a perspective view of an embodiment of a cathode
head and planar electron emitter with an adjustable height.
[0027] FIG. 3A is a perspective view of an embodiment of a planar
electron emitter coupled to electrical leads.
[0028] FIG. 3B is a top view of an embodiment of a pattern for a
planar electron emitter.
[0029] FIG. 3C is a cross-sectional view of embodiments of
cross-sectional profiles of rungs of a planar electron emitter.
[0030] FIG. 4 is a top view of an embodiment of a pattern for a
planar electron emitter that identifies certain locations of the
pattern for design optimization.
[0031] FIGS. 5A-5B are top views of temperature profiles of an
embodiment of a planar electron emitter for different maximum
temperatures.
[0032] FIGS. 6A-6B are top views of embodiments of cutout portions
in a planar electron emitter.
[0033] FIG. 7A shows an embodiment of an anode quadrupole core.
[0034] FIG. 7B shows an embodiment of a cathode quadrupole
core.
[0035] FIGS. 8A-8B are top views of components of one embodiment of
a quadrupole magnetic system.
[0036] FIG. 9 is a functional block diagram showing one embodiment
of a magnetic control for the quadrupole magnetic system of FIGS.
8A-8B.
[0037] FIG. 10 is a flow chart showing one embodiment of a process
control for magnetic control.
[0038] FIGS. 11A-11C are each a schematic diagram showing an
example of magnetic fields resulting from quadrupole fields, with
FIG. 11A showing a focused quadrupole field that is not shifted,
FIG. 11B shows a focused quadrupole field that is shifted in the
x-direction, and FIG. 11C shows a focused quadrupole shifted in the
y-direction.
[0039] FIGS. 12A-12B are top views of components of one embodiment
of a quadrupole magnetic system.
[0040] FIG. 12C is a functional block diagram showing one
embodiment of a magnetic control for the quadrupole magnetic system
of FIGS. 12A-12B.
[0041] FIG. 13 is a perspective view of internal components of an
embodiment of an X-ray tube.
[0042] FIG. 14A shows an embodiment of an anode core.
[0043] FIG. 14B shows an embodiment of a cathode core.
[0044] FIGS. 15A-15B are top views of components of one embodiment
of a magnet system.
[0045] FIG. 15C is a functional block diagram showing one
embodiment of a magnetic control for the magnetic system of FIGS.
15A-15B.
[0046] FIGS. 16A-16B are top views of components of one embodiment
of a magnet system.
[0047] FIG. 17A is a perspective view of an example X-ray tube in
which an embodiment of a three core magnetic system is
implemented.
[0048] FIG. 17B is a side view of the X-ray tube of FIG. 17A.
[0049] FIG. 17C is a cross-sectional view of the X-ray tube of FIG.
17A.
[0050] FIG. 17D is a perspective view of internal components of an
embodiment of an example X-ray tube having a three core magnetic
system.
[0051] FIG. 18A is a top view of an embodiment of an anode
quadrupole core.
[0052] FIG. 18B is a top view of an embodiment of a cathode
quadrupole core.
[0053] FIG. 18C is a top view of an embodiment of a dipole
core.
[0054] FIG. 18D is a top view of another embodiment of a dipole
core.
[0055] FIG. 19A is a top view of one embodiment of a cathode
quadrupole magnet system.
[0056] FIG. 19B is a top view of one embodiment of an anode
quadrupole magnet system.
[0057] FIG. 20A is a top view of one embodiment of a dipole magnet
system.
[0058] FIG. 20B is a top view of another embodiment of a dipole
magnet system.
[0059] FIGS. 21A-21B are functional block diagrams, each showing
one embodiment of a magnetic control.
DETAILED DESCRIPTION
[0060] In the following detailed description, reference is made to
the accompanying drawings, which form a part hereof. In the
drawings, similar symbols typically identify similar components,
unless context dictates otherwise. The illustrative embodiments
described in the detailed description, drawings, and claims are not
meant to be limiting. Other embodiments may be utilized, and other
changes may be made, without departing from the spirit or scope of
the subject matter presented herein. It will be readily understood
that the aspects of the present disclosure, as generally described
herein, and illustrated in the figures, can be arranged,
substituted, combined, separated, and designed in a wide variety of
different configurations, all of which are explicitly contemplated
herein.
I. General Overview of an Exemplary X-Ray Tube
[0061] Embodiments of the present technology are directed to X-ray
tubes of the type having a vacuum housing in which a cathode and an
anode are arranged. The cathode includes an electron emitter that
emits electrons in the form of an electron beam that is
substantially perpendicular to a face of the emitter, and the
electrons are accelerated due to a voltage difference between the
cathode and the anode so as to strike a target surface on the anode
in an electron region referred to as a focal spot. Embodiments can
also include electron beam focusing and/or steering components that
are cooperatively configured to manipulate the electron beam by:
(1) deflecting, or steering, the electron beam, and thereby
altering the position of the focal spot on the anode target; and/or
(2) focusing the electron beam so as to alter the dimensions of the
focal spot. Different embodiments utilize different configurations
of such focusing and/or steering components, such as magnet
systems, including combinations of electromagnets formed as
quadrupoles and/or as dipoles via coil elements with current
flowing therein and disposed on a carrier/yoke comprised of a
suitable material.
[0062] Disclosed embodiments illustrate an electron emitter having
a planar electron emitter structure. Moreover, the planer emitter
is designed and configured to provide tunable emission
characteristics for the emitted electron beam, which results in the
ability to tailor--and thus optimize--the focal spot size, shape
and position for a given imaging application. The tailoring of the
planar electron emitter pattern can result in an enhanced emitter
configuration that avoids image quality issues due to a
less-than-optimal focal spot. For example, an increase in spatial
resolution and reduction in image artifacts is possible with the
designed planer electron emitter patterns. However, the planar
emitter described herein can be used in various X-ray tube
embodiments, such as those with or without beam focusing and/or
steering.
[0063] In general, example embodiments described herein relate to a
cathode assembly with a planar electron emitter that can be used in
substantially any X-ray tube, such as for example, in long throw
length X-ray tubes. In at least some of the example embodiments
disclosed herein, the difficulties associated with a long throw
length of an X-ray tube can be overcome by employing a planar
electron emitter having a planar emitting surface. In a disclosed
embodiment, the planar emitting surface can be formed by a
continuous and cutout shaped planar member with a substantially
flat emitting surface that extends between two electrodes. The
continuous flat emitting surface can have a plurality of sections
connected together at bends or elbows that are defined by the
cutout. When a suitable electrical current is passed through the
emitter, the planar emitting surface emits electrons that form an
electron beam that is substantially laminar as it propagates
through an acceleration region and a drift region (e.g., with or
without magnetic steering or focusing) to impinge upon a target
surface of an anode at a focal spot.
[0064] In yet another embodiment, an electron source is provided in
the form of a flat emitter for the production of electrons. The
emitter has a relatively large emitting area with design features
that can be tuned to produce the desired distribution of electrons
to form a primarily laminar beam. The emission over the emitter
surface is not uniform or homogenous; it is tuned to meet the needs
of a given application. As the beam flows from the cathode to the
anode, the electron density of the beam spreads the beam apart
significantly during transit. The increased beam current levels
created by higher power requirements exacerbate the spreading of
the beam during transit. In disclosed embodiments, to achieve the
focal spot sizes required, the beam is focused by two quadrupoles
as it transits from the cathode to the anode. This also provides
for creating a multiplicity of sizes from a single emitter; the
size conceivably could be changed during an exam as well. The
increased emitter area of the flat geometry of the emitter allows
production of sufficient electrons flowing laminarly to meet the
power requirements. To address the requirement of steering the beam
in two dimensions so as to provide the desired imaging
enhancements, a pair of dipoles is used to deflect the beam to the
desired positions at the desired time. One dipole set is provided
for each direction.
[0065] Certain embodiments include a magnetic system implemented as
two magnetic quadrupoles disposed in the electron beam path of an
X-ray tube. The quadrupoles are configured to focus in both
directions perpendicular to the beam path, and to steer the beam in
both directions perpendicular to the beam path. The two quadrupoles
form a magnetic lens (sometimes referred to as a "doublet") and the
focusing is accomplished as the beam passes through the quadrupole
lens. The steering is accomplished by offsetting the coil
alternating current in one quadrupole coil or corresponding pairs
of the quadrupole coils while maintaining the focusing coil
constant current which results in an overall shift in the
quadrupole's magnetic field. Steering of the beam occurs through
appropriate coil or coil pair energizing and can be done in one
axis or a combination of axes perpendicular to the beam path. In
one example, one quadrupole is used to focus in the first direction
and the second quadrupole to focus in the second direction as well
as steer in both directions. The two quadrupoles together form the
quadrupole lens.
[0066] The embodiments can include an electron beam focusing
component that includes two magnetic quadrupole cores. A quadrupole
core is considered to be any core that has a quadrupole for beam
focusing. Generally, each magnetic quadrupole core can have a yoke
with four pole projections evenly distributed therearound, and each
pole projection can include a quadrupole electromagnetic coil so
that all four electromagnets provide the magnetic quadrupole
moment. One quadrupole core can narrow the electron beam in the
length direction, and the other quadrupole core can narrow the
electron beam in the width direction. Thereby, the combination of
the two quadrupole cores can cooperate to focus the electron beam,
which allows precise length and width dimension control of the
focal spot on the anode. However, either or both quadrupole cores
can focus in the length and width directions. The quadrupoles can
include coils that have constant current to achieve the focusing
effect. Also, a pulse width modulated circuit coupled with the
coils can create constant current in the coils because the coils
are current integrating devices. For example, a current pulse train
into the coil can cause the coil to create a constant current in
the coil, which can be changed by changing the current pulse train.
Also a DC power supply can provide constant current (e.g., DC
current).
[0067] In one embodiment, the cathode emits an electron beam that
flows from the cathode toward the anode such that the beam spreads
the electrons apart during transit, and one or more of the
quadrupole cores focus the electron beam to a defined focal spot.
In one aspect, both quadrupole cores provide a focusing effect on
the electron beam. This allows for both beam width (e.g., X axis)
and beam length (e.g., Y axis) focusing, wherein one quadrupole
core focuses in the length and the other quadrupole core focuses in
the width. This also allows for the ability of the X-ray tube to
create a plurality of different types of focal spot sizes and
shapes from a single planar emitter, where such changes of focusing
and change of beam length and/or width can be performed during
imaging, such as during a CT examination.
[0068] In one embodiment, the X-ray tube can perform beam focusing
with high magnetic flux in a small throw volume or space. The
magnetic material suitable for high magnetic flux can be a material
that does not saturate and can be used for the quadrupole cores in
the yokes, such as the yokes for two adjacent quadrupole cores.
Also, the quadrupole pole projections can be the same material as
the yokes. Such a material can be iron.
[0069] However, movement of the X-ray in the Z axis may be
desirable, and due to the angle of the anode target surface,
steering of the electron beam in the Y axis can cause the X-ray to
move in the Z axis.
[0070] The embodiments can include an electron beam steering
component that includes one of the magnetic quadrupole cores being
configured to operate each quadrupole electromagnet separately to
change the magnetic field in order to move the electron beam in two
dimensions away from the central axis, such as movement of the
focal spot on the anode target surface. The quadrupole core closest
to the anode (e.g., anode quadrupole core) can have a yoke with
four pole projections evenly distributed therearound that each have
a quadrupole magnetic coil with independent current control.
Accordingly, the anode quadrupole core can have electromagnet coils
wound around the pole projections on the yoke that can steer the
electron beam in any direction or toward any quadrant. The anode
quadrupole core can impart a magnetic field that nudges and
deflects the electron beam, and then the electron beam coasts to
the target anode. However, the quadrupole core closest to the
cathode (e.g., cathode quadrupole core) can be configured for
focusing and steering while the anode quadrupole core only focuses.
In an alternative configuration, the cathode quadrupole core can
focus and steer in a first direction, and the anode quadrupole core
can focus and steer in a second direction that is perpendicular to
the first direction.
[0071] Steering can be accomplished by moving the center of the
quadrupole field away from a central axis, where the central axis
can be the natural (e.g., unperturbed) electron beam axis or
aligned central axis of the quadrupole cores. Introducing an AC
offset to one coil, a pair of coils, three coils, or two pair of
coils of the coils of the quadrupole cores can provide the shift of
the quadrupole field. This may be an asymmetric quadrupole field
that has focusing that is focused off the central axis. The
quadrupole field can be shifted off axis from the central axis or
off the central axes of the cores. The quadrupole still provides
focusing by the center being shifted off axis, and the electron
beam follows the center of the shifted quadrupole field. While the
constant focusing current provides focusing, the AC offset to one
coil or a pair of coils or three coils or two pairs of coils can
shift the center of the quadrupole field away from center of the
quadrupole cores. The shifted quadrupole field is similar to a
dipole effect being superimposed over a quadrupole field. The AC
offset to each coil for a core can be independent and different to
get steering. The AC offset to one or more coils can apply to the
steering coils and dipole coils of the different embodiments. The
AC offset can be time vary steering current.
[0072] The embodiments can include an electron beam steering
component that includes one of the magnetic quadrupole cores having
at least one steering coil, or a pair or two orthogonal pairs of
steering coils collocated on the pole projections with quadrupole
coils. Each pair of steering coils can be included on a pair of
oppositely disposed pole projections and collocated with
electromagnetic quadrupole coils. The steering system can be
configured to operate each steering coil separately to shift the
quadrupole magnetic field in order to move the electron beam on the
focal spot on the anode target surface. In one aspect, the
quadrupole core closest to the anode (e.g., anode quadrupole core)
can have a yoke with four pole projections evenly distributed
therearound that each have a quadrupole electromagnetic coil and a
steering coil with independent current control. Accordingly, the
anode quadrupole core can have quadrupole and steering coils wound
around the pole projections on the yoke. The anode quadrupole core
can steer the electron beam in any direction or toward any quadrant
relative to the electron beam axis by independently operating the
different steering coils. The steering coils can modulate the
quadrupole magnetic field that nudges and deflects the electron
beam, and then the electron beam coasts to the target anode.
However, the quadrupole core closest to the cathode (e.g., cathode
quadrupole core) can be configured for focusing with quadrupole
coils and steering with steering coils, while the anode quadrupole
core only focuses with quadrupole coils. In an alternative
configuration, the cathode quadrupole core can focus and steer in a
first direction, and the anode quadrupole core can focus and steer
in a second direction that is perpendicular to the first direction,
whereby the combination of both cores can be configured in such a
manner to steer the electron beam in any direction desired.
[0073] Steering can be accomplished by moving the center of the
quadrupole field away from a central axis, where the central axis
can be the natural (e.g., unperturbed) electron beam axis or
aligned central axis of the quadrupole cores or central axis of the
X-ray tube. Introducing an AC offset to at least one of the
steering coils of the quadrupole cores can provide the shift of the
quadrupole field. This may be an asymmetric quadrupole field that
has focusing that is focused off the central axis. The quadrupole
field can be shifted off axis from the central axis or off the
central axes of the cores. The quadrupole still provides focusing
with the center being shifted off axis, and the electron beam
follows the center of the shifted quadrupole field. While the
constant focusing current in the quadrupole coils provides
focusing, the AC offset in at least one steering coil can shift the
center of the quadrupole field away from center of the quadrupole
cores. The shifted quadrupole field is similar to a dipole effect
being superimposed over a quadrupole field. The AC offset to each
coil of a core can be independent and different to perform the
steering of the electron beam. The AC offset can be time vary
steering current.
[0074] Embodiments can include an electron beam steering component
that includes one magnetic dipole core that has two different
dipole pairs. The dipole core can have a yoke with four
electromagnets evenly distributed therearound so as to form two
dipole pairs that are orthogonal. The electromagnets can be wound
around the yoke, or alternatively the electromagnetics can be wound
around pole protrusions on the yoke. The dipole core can steer the
electron beam in any direction or toward any quadrant. The dipole
core can impart a magnetic field that nudges and deflects the
electron beam, and then the electron beam coasts to the target
anode. This gives precise location control for the spot. The dipole
coils on the dipole core can be operated similarly to the steering
coils described herein.
[0075] Certain embodiments include a magnetic system implemented as
two magnetic quadrupole cores and one magnetic dipole core disposed
in the electron beam path of an X-ray tube. The quadrupole cores
are configured to focus in both directions perpendicular to the
beam path. The primary steering function is accomplished by
offsetting the coil current in corresponding magnetic pairs of the
dipole (e.g., two orthogonal dipole pairs) which results in an
overall shift in the magnetic field to nudge the electrons in a
certain direction. Steering of the beam occurs through appropriate
coil pair energizing of both dipole coil pairs, and can be done in
one axis or a combination of axes.
[0076] Certain embodiments include a magnetic system implemented as
two magnetic quadrupoles and two magnetic dipoles disposed in the
electron beam path of an X-ray tube. The two magnetic quadrupoles
are configured to focus the electron beam path in both directions
perpendicular to the beam path. The two magnetic dipoles are
collocated on a common dipole core and configured to steer the beam
in both directions perpendicular to the beam path, which can
provide four quadrant steering. The steering is accomplished by the
two dipoles which are created by coils wound on the dipole core
pole protrusions. The focusing is accomplished by the quadrupole
coils being wound on the quadrupole pole protrusions of the two
quadrupole cores so as to maintain the focusing coil current.
Steering of the beam occurs through appropriate dipole coil pair
energizing and can be done in one axis or a combination of axes
perpendicular to the electron beam path. In one embodiment, one
quadrupole is used to focus in the first direction and the second
quadrupole to focus in the second direction, and the dipole is used
to steer the electron beam in both directions. However, only one
coil of a dipole coil pair may receive the AC Offset and the other
receives zero AC offset. The dipole coils may be considered to be
steering coils and operate as described for the steering coils.
[0077] In one embodiment, the dipole core can include a magnetic
material that has high dynamic response, which material can be used
for the yoke. The material can have less magnetic flux than the
material of the quadrupole cores. The material of the dipole core
can be configured so that it does not saturate at low levels, and
it responds several orders of magnitude faster than the iron
material used for the quadrupole cores. The dipole core material
can be iron based ferrite with lower saturation flux levels, which
allows for high magnetic switching speeds. The material allows up
to 7 kHz switching and as low as about 20 microseconds transitions.
In one aspect the dipole core material can be a ferrite material.
The ferrite can be an iron ceramic, such as iron oxide, which can
have different magnetic characteristics compared to the quadrupole
core material. The material of the quadrupole cores can be iron.
However, one quadrupole core can include the ferrite material.
[0078] In one embodiment, the X-ray tube having the two quadrupole
cores and one dipole core can be configured for high flux in the
two quadrupole cores and fast response in the one dipole core.
Thus, the dipole core material can be different from the quadrupole
core material. The same material can be used for the yoke and the
pole protrusions.
[0079] The dipole core can include pole protrusions that have
dipole coils wrapped therearound for the electromagnets. On the
other hand, the dipole core can include the dipole coils wrapped
around the annular body of the dipole core at different and
opposing locations, where dipole coils wrapped around the annular
body can be between pole protrusions, if pole protrusions are
included. In one aspect, the dipole core can be devoid of dipole
coils on pole protrusions, and the dipole coils can be wrapped at
four locations around the yoke. The dipole core can have the dipole
coils and/or dipole pole projections staggered from the quadrupole
coils of the quadrupole cores, such as at 45 degrees therefrom.
[0080] In one embodiment, the X-ray tube having the two quadrupole
cores and one dipole core can be separated from each other such
that focusing quadrupole cores are separate from the steering
dipole core. The beam steering can be operated at higher rates,
such as in the kHz range. The X-ray tube can provide the user with
enhanced imaging and more capability to enrich the CT data sets
with reduced radiation dose. This can allow the X-ray tube to be
used in advanced imaging methods. This can also allow the X-ray
tube to perform higher flux focusing with the focusing cores to
create small focal spots without saturation in the core
material.
[0081] In one embodiment, the X-ray tube can include the two
quadrupoles having the pole protrusions and the electromagnets
aligned, which can be referenced at 0, 90, 180, and 270 degrees.
The dipole core can have the electromagnets staggered from those of
the quadrupole cores, which staggering can result in the
electromagnets being at about 45, 135, 225, and 315 degrees.
[0082] In one embodiment, the X-ray tube can include 0 degrees on
an axis, and the two quadrupoles having the pole protrusions and
the electromagnets aligned, which can be referenced at 45, 135, 225
and 315 degrees. The dipole core can have the electromagnets
staggered from those of the quadrupole cores, which staggering can
result in the electromagnets being at about 0, 90, 180, and 270
degrees. This can be seen in FIGS. 18C and 20A.
[0083] In one embodiment, the dipole core coils are being
controlled independently by the method shown in FIG. 20B, thereby
the dipole pole protrusions are in line with the quadrupole pole
protrusions at 45, 135, 225 and 315 degrees.
[0084] In one embodiment, the dipole core can have dipole coils on
the pole protrusions that each have their own supply line for power
and operation, which can be independently controlled. The 45 degree
offset allows for two separate supply systems, one for the two
quadrupole cores and one for the dipole core. This allows for an
easier implementation of the electronics for the dipole core.
[0085] In one embodiment, the X-ray tube can be configured with a
steering coil pair in the x and z plane and a steering coil pair in
the x and y plane, which can provide for a reference axis going in
and out of the page. The steering coil pairs are configured to move
the beam in the x direction, the control can energize at least one
steering coil of a first steering coil pair. If there is a desire
to move the beam in the z direction, the control can energize one
steering coil of the second steering coil pair.
[0086] In one embodiment, operation of the X-ray tube can allow for
steering at about 6 or 7 kHz and the gentry of the X-ray machine
rotates at about 4 Hz, which allows for data collection at six
spots for a selected position. This allows for six focal spot
positions to be recorded in the time previously one focal spot
position was available.
[0087] In one embodiment, the X-ray tube can be included in an
X-ray system, such as a CT system, and can include electron beam
control. The X-ray tube can have high power with focusing and
2-dimensional beam movement controllability with a short or a long
throw between the cathode and anode. The X-ray tube can control the
beam to a defined emission area for the beam or focal spot area or
shape or location on the anode. The X-ray tube can focus the
electron beam in two dimensions under active beam manipulation by a
cathode quadrupole core and anode quadrupole core. The X-ray tube
can steer the electron beam in two dimensions under active beam
manipulation by a steering core having independent control of at
least two of the steering coils, preferably all four steering
coils. Alternatively, at least one coil of an opposing pair of
quadrupole coils can be provided with AC offset so as to modulate
the quadrupole field to cause beam steering. Such beam steering can
be implemented in imaging methods to provide a richer CT data set,
where the rich CT data set can be used to improve resolution of an
image from the CT. The improved resolution can improve resolution
in the slice and row directions of the CT, for example, as per
being received (e.g., seen) by the detector. Beam steering can be
useful to implement data oversampling of the X-ray by allowing for
multiple focal spot locations for a given X-ray imaging time
duration.
[0088] In one embodiment, a steering core configured for focusing
and steering with a quadrupole field can include a magnetic
material that has high dynamic response, which material can be used
for the yoke and pole projections. The material can have less
magnetic flux than the material of a quadrupole core that is
configured for only focusing. The material of the steering core can
be configured so that it does not saturate at low levels, and it
responds to several orders of magnitude faster than the iron
material used for the focusing-only quadrupole core. The steering
core material can be iron based ferrite with lower saturation flux
levels. However, the ferrite material allows for the quadrupole
core to respond to flux changes much faster compared to iron, which
is beneficial for switching magnetic fields, such as in steering.
The material allows up to 7 kHz switching and as low as about 20
microseconds transitions. In one aspect, the steering core material
can be a ferrite material. The ferrite can be an iron ceramic, such
as iron oxide, which can have different magnetic characteristics
compared to the focusing-only quadrupole core material.
[0089] In one embodiment, the pole faces of the pole projections
can have a reduced profile, such as from 1/4 to 3/8 inches across.
This can include the pole faces of any of the pole projections,
such as for the focusing or steering cores.
[0090] In one embodiment, a steering core can have two or four
steering coils on the pole projections that each has its own supply
line for power and operation, which can be independently
controlled.
[0091] In one embodiment, the cores can each include fluidic
pathways fluidly coupled to a coolant system, which allows coolant
to flow through the yokes, and optionally through the pole
projections. As such, each pole projection can have a fluid inlet
pathway and a fluid outlet pathway coupled to a fluid pathway in
the yoke.
[0092] In one embodiment, the X-ray tube can include the two
quadrupole cores having yokes with the pole projections and the
quadrupole coils aligned, which can be referenced at 0, 90, 180,
and 270 degrees. The steering coils can be collocated on the pole
projections with the quadrupole coils.
[0093] In one embodiment, the X-ray tube can include 0 degrees on
an axis, and the two quadrupole cores having yokes with the pole
projections and the quadrupole coils are aligned, which can be
referenced at 45, 135, 225 and 315 degrees. The steering coils can
be collocated on the pole projections with the quadrupole
coils.
[0094] FIGS. 1A-1C are views of one example of an X-ray tube 100 in
which one or more embodiments described herein may be implemented.
Specifically, FIG. 1A depicts a perspective view of the X-ray tube
100 and FIG. 1B depicts a side view of the X-ray tube 100, while
FIG. 1C depicts a cross-sectional view of the X-ray tube 100. The
X-ray tube 100 illustrated in FIGS. 1A-1C represents an example
operating environment and is not meant to limit the embodiments
described herein.
[0095] Generally, X-rays are generated within the X-ray tube 100,
some of which then exit the X-ray tube 100 to be utilized in one or
more applications. The X-ray tube 100 may include a vacuum
enclosure structure 102 which may act as the outer structure of the
X-ray tube 100. The vacuum enclosure structure 102 may include a
cathode housing 104 and an anode housing 106. The cathode housing
104 may be secured to the anode housing 106 such that an interior
cathode volume 103 is defined by the cathode housing 104, and an
interior anode volume 105 is defined by the anode housing 106, each
of which are joined so as to define the vacuum enclosure 102.
[0096] In some embodiments, the vacuum enclosure structure 102 is
disposed within an outer housing (not shown) within which a
coolant, such as liquid or air, is circulated so as to dissipate
heat from the external surfaces of the vacuum enclosure 102. An
external heat exchanger (not shown) is operatively connected so as
to remove heat from the coolant and recirculate it within the outer
housing.
[0097] The X-ray tube 100 depicted in FIGS. 1A-1C includes a shield
component 107 (e.g., sometimes referred to as an electron shield,
aperture, or electron collector) that is positioned between the
anode housing 106 and the cathode housing 104 so as to further
define the vacuum enclosure 102. The cathode housing 104 and the
anode housing 106 may each be welded, brazed, or otherwise
mechanically coupled to the shield 107. While other configurations
can be used, examples of suitable shield implementations are
further described in U.S. patent application Ser. No. 13/328,861
filed Dec. 16, 2011 and entitled "X-ray Tube Aperture Having
Expansion Joints," and U.S. Pat. No. 7,289,603 entitled "Shield
Structure And Focal Spot Control Assembly For X-ray Device," the
contents of each of which are incorporated herein by reference for
all purposes.
[0098] The X-ray tube 100 may also include an X-ray transmissive
window 108. Some of the X-rays that are generated in the X-ray tube
100 may exit through the window 108. The window 108 may be composed
of beryllium or another suitable X-ray transmissive material.
[0099] With specific reference to FIG. 1C, the cathode housing 104
forms a portion of the X-ray tube referred to as a cathode assembly
110. The cathode assembly 110 generally includes components that
relate to the generation of electrons that together form an
electron beam, denoted at 112. The cathode assembly 110 may also
include the components of the X-ray tube between an end 116 of the
cathode housing 104 and an anode 114. For example, the cathode
assembly 110 may include a cathode head 115 having an electron
emitter, generally denoted at 122, disposed at an end of the
cathode head 115. As will be further described, in disclosed
embodiments the electron emitter 122 can be configured as a planar
electron emitter. When an electrical current is applied to the
electron emitter 122, the electron emitter 122 is configured to
emit electrons via thermionic emission, that together form a
laminar electron beam 112 that accelerates towards the anode target
128.
[0100] The cathode assembly 110 may additionally include an
acceleration region 126 further defined by the cathode housing 104
and adjacent to the electron emitter 122. The electrons emitted by
the electron emitter 122 form an electron beam 112 and traverse
through the acceleration region 126 and accelerate towards the
anode 114 due to a suitable voltage differential. More
specifically, according to the arbitrarily-defined coordinate
system included in FIGS. 1A-1C, the electron beam 112 may
accelerate in a z-direction, away from the electron emitter 122 in
a direction through the acceleration region 126.
[0101] The cathode assembly 110 may additionally include at least
part of a drift region 124 defined by a neck portion 124a of the
cathode housing 104. In this and other embodiments, the drift
region 124 may also be in communication with an aperture 150
provided by the shield 107, thereby allowing the electron beam 112
emitted by the electron emitter 122 to propagate through the
acceleration region 126, the drift region 124 and aperture 150
until striking the anode target surface 128. In the drift region
124, a rate of acceleration of the electron beam 112 may be reduced
from the rate of acceleration in the acceleration region 126. As
used herein, the term "drift" describes the propagation of the
electrons in the form of the electron beam 112 through the drift
region 124.
[0102] Positioned within the anode interior volume 105 defined by
the anode housing 106 is the anode 114. The anode 114 is spaced
apart from and opposite to the cathode assembly 110 at a terminal
end of the drift region 124. Generally, the anode 114 may be at
least partially composed of a thermally conductive material or
substrate, denoted at 160. For example, the conductive material may
include tungsten or molybdenum alloy. The backside of the anode
substrate 160 may include additional thermally conductive material,
such as a graphite backing, denoted by way of example here at
162.
[0103] The anode 114 may be configured to rotate via a rotatably
mounted shaft, denoted here as 164, which rotates via an
inductively induced rotational force on a rotor assembly via ball
bearings, liquid metal bearings or other suitable structure. As the
electron beam 112 is emitted from the electron emitter 122,
electrons impinge upon a target surface 128 of the anode 114. The
target surface 128 is shaped as a ring around the rotating anode
114. The location in which the electron beam 112 impinges on the
target surface 128 is known as a focal spot (not shown). Some
additional details of the focal spot are discussed below. The
target surface 128 may be composed of tungsten or a similar
material having a high atomic ("high Z") number. A material with a
high atomic number may be used for the target surface 128 so that
the material will correspondingly include electrons in "high"
electron shells that may interact with the impinging electrons to
generate X-rays in a manner that is well known.
[0104] During operation of the X-ray tube 100, the anode 114 and
the electron emitter 122 are connected in an electrical circuit.
The electrical circuit allows the application of a high voltage
potential between the anode 114 and the electron emitter 122.
Additionally, the electron emitter 122 is connected to a power
source such that an electrical current is passed through the
electron emitter 122 to cause electrons to be generated by
thermionic emission. The application of a high voltage differential
between the anode 114 and the electron emitter 122 causes the
emitted electrons to form an electron beam 112 that accelerates
through the acceleration region 126 and the drift region 124
towards the target surface 128. Specifically, the high voltage
differential causes the electron beam 112 to accelerate through the
acceleration region 126 and then drift through the drift region
124. As the electrons within the electron beam 112 accelerate, the
electron beam 112 gains kinetic energy. Upon striking the target
surface 128, some of this kinetic energy is converted into
electromagnetic radiation having a high frequency, i.e., X-rays.
The target surface 128 is oriented with respect to the window 108
such that the X-rays are directed towards the window 108. At least
some portion of the X-rays then exit the X-ray tube 100 via the
window 108.
[0105] Additionally, FIG. 1C shows a cross-sectional view of an
embodiment of a cathode assembly 110 that can be used in the X-ray
tube 100 with the planar electron emitter 122 and magnetic system
200 described herein. As illustrated, a throw path between the
electron emitter 122 and target surface 128 of the anode 114 can
include the acceleration region 126, drift region 124, and aperture
150 formed in shield 107. In the illustrated embodiment, the
aperture 150 is formed via aperture neck 154 and an expanded
electron collection surface 156 that is oriented towards the anode
114.
[0106] Optionally, one or more electron beam manipulation
components can be provided. Such devices can be implemented so as
to "steer" and/or "deflect" the electron beam 112 as it traverses
the drift region 124, thereby manipulating or "toggling" the
position of the focal spot on the target surface 128. Additionally
or alternatively, a manipulation component can be used to alter or
"focus" the cross-sectional shape of the electron beam and thereby
change the shape of the focal spot on the target surface 128. In
the illustrated embodiments electron beam focusing and steering are
provided by way of a magnetic system denoted generally at 180.
[0107] The magnetic system 180 can include various combinations of
focusing quadrupoles, steering quadrupoles, steering coils, and
steering dipoles implementations that are disposed so as to impose
magnetic forces on the electron beam 112 so as to focus and/or
steer the beam. One example of the magnetic system 180 is shown in
FIGS. 1A-1D. In this embodiment, the magnetic system 180 is
implemented as two magnetic cores 182, 184 disposed in the electron
beam path 112 of the X-ray tube 100. The combination of the two
cores 182, 184 are configured to (a) focus in both directions
perpendicular to the beam path, and (b) to steer the beam in both
directions perpendicular to the beam path. In this way, the two
cores 182, 184 can have quadrupoles that act together to form a
magnetic lens (sometimes referred to as a "doublet"), and the
focusing and steering is accomplished as the electron beam passes
through the quadrupole "lens." The "focusing" provides a desired
focal spot shape and size. Additionally, the magnetic system 180
can be configured with at least one coil or a pair of coils that
have an AC offset, and preferably two perpendicular pairs of coils
that have an AC offset, used for steering. The steering can be
implemented by configurations of the two cores 182 and 184 as
described herein as well as an embodiment that utilizes three
cores, which is described in more detail herein. Accordingly, the
"steering" affects the positioning of the focal spot on the anode
target surface 128. The magnetic system 180 may be substituted with
any of the other magnetic systems described herein.
[0108] FIG. 1D shows the components of the X-ray device 100 that
are arranged for electron emission, electron beam steering and/or
focusing, and X-ray emission. In FIG. 1D, disposed within the beam
path is the magnetic system 180 configured to focus and steer the
electron beam before reaching the anode 114, as noted above. A
portion of the cathode assembly 110 has the cathode head 115 with
the electron emitter 122 on an end of the cathode head 115 so as to
be oriented or pointed toward the anode 114 (see FIG. 1C for
orientation). The cathode head 115 can include a head surface 119
that has an emitter region that is formed as a recess that is
configured to receive the electron emitter 122 (e.g., planar
electron emitter). The head surface 119 also includes electron beam
focusing elements 111 located on opposite sides of the electron
emitter 122. However, the magnetic system 180 may be substituted or
modified to include any of the components of any of the magnetic
systems described herein, such as the different two core
embodiments or three core embodiments.
II. Example Embodiments of a Planar Emitter with Tunable Emission
Characteristics
[0109] FIG. 2A illustrates a portion of the cathode assembly 110,
such as from FIGS. 1A-1C, which has a cathode head 15 with a planar
electron emitter 22 on an end of the cathode head 15 so as to be
oriented or pointed toward the anode 14 (e.g., see FIG. 1C-1D for
orientation). The cathode head 15 can include a head surface 19
that has an emitter region 23 that is formed as a recess in surface
19 that is configured to receive the planar electron emitter 22,
which further includes a first lead receptacle 25a configured to
house a first lead 27a of the electron emitter 22 and second lead
receptacle 25b configured to house a second lead 27b of the
electron emitter 22 (see FIG. 2B). The emitter region 23 can have
various configurations, such as a flat surface or the illustrated
recess shaped to receive the electron emitter 22, and the first and
second lead receptacles 25a-b can be conduits extending into the
body of the cathode head 15. The electron emitter 22 includes an
emitter body 29 that is continuous from the first lead 27a to the
second lead 27b and forms an emitter pattern 30. The head surface
19 also includes electron beam focusing elements 11 located on
opposite sides of the electron emitter 22.
[0110] FIG. 2B illustrates an embodiment of an internal region of
the cathode head 15 that shows electrical leads 27a, 27b for the
planar electron emitter 22. As shown, a base 21 can be dimensioned
to receive the cathode head 15 thereover. The base 21 can include a
lead housing 17 protruding from a base surface 21a. The lead
housing 17 can include a lead housing surface 17a that has the
first lead receptacle and second lead receptacle formed therein.
The first lead receptacle houses the first lead 27a, and the second
lead receptacle houses the second lead 27b. The first lead 27a is
electrically coupled to a first leg 31a, and the second lead 27b is
electrically coupled to a second leg 31b. The electrical coupling
may be structurally reinforced with a mechanical coupling between
the leads 27a, 27b with the legs 31a, 31b. The mechanical coupling
can be by welding, brazing, adhesive, mechanical coupling or other
coupling that keeps the first and second leads 27a, 27b physically
and mechanically coupled with the corresponding first and second
legs 31a, 31b. The first and second leads 27a, 27b can be
electrically connected to the cathode assembly 110 as known in the
art.
[0111] FIG. 2C shows the cathode head 15 to have an emitter height
adjustment mechanism 10, which includes a rotating member 12 and an
elevating member 14. Rotation of the rotating member 12 in one
direction elevates the emitter 22, and rotation of the rotating
member 12 in the other direction sinks the emitter 22 relative to
the cathode head surface 19. The raising of the emitter 22 can be
by the cathode head surface 19 lowering relative to the emitter 22,
and the lowering of the emitter 22 can be by the cathode head
surface 19 raising relative to the emitter 22. In one option, the
emitter 22 raises or lowers and the surface 19 stays fixed by
rotating member 12 relative to elevating member 14. In one option,
the emitter 22 stays fixed and the surface 19 raises or lowers by
rotating member 12 relative to elevating member 14. In one aspect,
the emitter can be attached to the base, and the elevating member
14 raises so that the surface 19 raises relative to the emitter 22.
The rising and sinking of the emitter 22 by the adjustment
mechanism 10 can be relative to the head surface 19. As such, the
emitter 22 can be elevated or sunk relative to a recess 16 in the
head surface 19, where the recess 16 can be shaped and dimensioned
to accommodate the emitter 22 therein. The elevating member 14 may
rise or lower while the emitter 22 stays at a fixed height.
However, a modification can be the rotation of the rotating member
12 and the elevating member 14 elevating the emitter 22 up or down
and the surface 19 staying at a fixed height.
[0112] The cathode head 15 can include a head surface 19 that has
an emitter region 23 that is formed as a recess 16 in head surface
19 that is configured to receive the electron emitter 22, which
further includes a first lead receptacle 25a configured to house a
first lead of the electron emitter 22 and second lead receptacle
25b configured to house a second lead of the electron emitter 22.
The emitter region 23 can have various configurations, such as a
flat surface or the illustrated recess 16 shaped to receive the
electron emitter 22, and the first and second lead receptacles
25a-b can be conduits extending into the body of the cathode head
15.
[0113] FIG. 3A illustrates an embodiment of the electron emitter 22
coupled with the first and second leads 27a, 27b. The emitter
pattern 30 can be two-dimensional so as to form a planar emitter
surface 34, where different regions of the emitter body 29
cooperate to form the planar emitter surface 34. There are gaps 32
(e.g., illustrated by lines between members) between different
regions of the emitter body 29, where the gaps 32 may form a first
continuous gap 32a from a first end 33a to a middle region 33c and
the gaps 32 may form a second continuous gap 32b from the middle
region 33c to a second end 33b of the planar emitter surface 34. As
illustrated, the middle region 33c of the planar emitter surface 34
is also the middle region of the electron emitter 22 and middle
region of the emitter body 29 and the emitter pattern 30. However,
other arrangements, configurations, or patterns may be implemented
to an electron emitter 22 so as to have a planar emitter surface
34.
[0114] The emitter body 29 can have various configurations;
however, one configuration includes at least one flat surface 41
(e.g., flat side, see FIG. 3C) that when patterned in a planer
emitter pattern 30 forms the planar electron emitter 22. That is,
the emitter body 29 is continuous and patterned so that electrical
current flows from the first lead 27a through the emitter body 29
in the emitter pattern 30 to the second lead 27b, or vice
versa.
[0115] In one aspect, no portions or regions of the emitter body 29
touch each other from the first end 33a to the second end 33b. The
emitter pattern 30 may be tortuous with one or more bends, straight
sections, curved sections, elbows or other features; however, the
emitter body 29 does not include any region that touches another
region of itself In one aspect, all of the sections between corners
or elbows are straight, which can avoid open windows or open
apertures of substantial dimension within the emitter pattern 30,
where openings of substantial dimensions can cause unwanted side
electron emission lateral of the throw path of the X-ray tube 100.
Thus, the electrical current only has one path from the first lead
27a to the second lead 27b, which is through the emitter body 29 in
the emitter pattern 30 from the first end 33a to the second end
33b. However, additional leads can be coupled to the emitter body
29 at various locations of the emitter pattern 30 so as to tune the
temperature and electron emission profiles. Examples of locations
and configurations of additional leads is described in more detail
below.
[0116] The planar layout (e.g., planar emitter pattern 30) of the
current path of the electron emitter 22 is created to produce a
tailored heating profile. The tailoring can be performed during the
design phase in view of various parameters of one or more end point
applications. Here, since the emission of electrons is thermionic,
emission can be controlled and matched to the desired emitting
region (e.g., one or more rungs 35, see FIG. 3B) of the electron
planar emitter surface 34 by designing the heating profile of the
emitting region. Further, tailoring the temperature and emission
profiles during design protocols allows the profile of the emitted
electron beam to be controlled and can be used to create the
desired one or more focal spots. This configuration of a planar
electron emitter 22 is in direct contrast to traditional helically
wound wire emitters, which do not create electron paths that are
perpendicular to the emitter surface, and therefore are not useful
in, for example, so-called "long throw" applications. Additionally,
the shape and size of a circular flat emitter limits total emission
and the shape does not easily facilitate tailoring the spot size
and shape to a particular application. On the other hand,
embodiments of the proposed planar electron emitter such as shown
in FIGS. 3A-3B can be scalable and the emitter form and pattern can
be designed to be tailored to various shapes and can be used in any
type of X-ray tube, including but not limited to long throw tubes,
short throw tubes, and medium throw tubes, as well as others. The
magnetic systems can also be used in any type of X-ray tube,
including but not limited to long throw tubes short throw tubes and
medium throw tubes, as well as others
[0117] FIG. 3A also shows that the first lead 27a can be coupled to
a first leg 31a at the first end 33a of the emitter body 29 and the
second lead 27b can be coupled a second leg 31b at the second end
33b of the emitter body 29. As shown, the first leg 31a is opposite
of the second leg 31b; however, in some configurations the first
leg 31a may be adjacent or proximal of the second leg 31b or at any
point on the emitter pattern 30.
[0118] In one embodiment, the electron emitter 22 can be comprised
of a tungsten foil, although other materials can be used. Alloys of
tungsten and other tungsten variants can be used. Also, the
emitting surface can be coated with a composition that reduces the
emission temperature. For example, the coating can be tungsten,
tungsten alloys, thoriated tungsten, doped tungsten (e.g.,
potassium doped), zirconium carbide mixtures, barium mixtures or
other coatings can be used to decrease the emission temperature.
Any known emitter material or emitter coating, such as those that
reduce emission temperature, can be used for the emitter material
or coating. Examples of suitable materials are described in U.S.
Pat. No. 7,795,792 entitled "Cathode Structures for X-ray Tubes,"
which is incorporated herein in its entirety by specific
reference.
[0119] FIG. 3B shows a top view of the electron emitter 22
described in connection to FIG. 3A. The top view allows for a clear
view of various features of the electron emitter 22 that are now
described in detail. The emitter body 29 includes rungs 35
connected together at corners 36 so as to form the emitter pattern
30, where the rungs 35 are the elongate members between the corners
36 and connected end to end (e.g., 35a-35o) at the corners 36 from
the first end 33a to the second end 33b. As shown in FIG. 3B, there
are four left side rungs 35a, 35e, 35i, 35m, four right side rungs
35c, 35g, 35k, 35o, three top rungs 35d, 35j, 35n, three bottom
rungs 35b, 35f, 35l, and a central rung 35h, which is based on
portrait page orientation. However, any number of rungs 35 from a
central rung 35h or central point to the outer rungs, to the right,
left, top or bottom, can be used as is reasonable. Also, the
emitter regions 35p, 35q between the central rung 35h and connected
rungs 35g, 35i may be considered rungs 35 or mini rungs, where
these emitter regions 35p, 35q are between the webs 37, which
results in four left, right, top, and bottom rungs. However, the
electron emitter 22 can include any number of rungs and in any
orientation or shape. Each corner 36 is shown to have a slot 38
protruding from the gap 32 into the corner 36. The body of the
corner 36 between the slot 38 and the apex of the corner is
referred to as a web 37, which is shown be a dashed line in the
corners 36. The web 37 can extend from the nadir (e.g., inside or
concave part) to the apex (e.g., outside or convex part). The slots
38 are all shown to extend from the gap 32 through the nadir toward
the apex; however, the slots 38 may extend from the apex toward the
nadir. When there is a slot 38 at the nadir, the nadir is
considered to be the intersection that would have occurred from the
connected rungs 35 had the slot 38 been absent, which results in
the nadir being in the slot. As such, the nadir is not at the
termination of a slot 38 within a corner 36. The apex and nadir are
the true apex and nadir without any slots or cutouts at the corner.
As shown, the gaps 32 separate all of the rungs 35 from each other
and all of the corners 36 from each other. This provides for a
single electrical path shown by the arrows from the first end 33a
to the second end 33b.
[0120] The rungs 35 can all be the same dimension (e.g., height
and/or width), all be different dimensions, or any combination of
same and different dimensions from the first end 33a to the second
end 33b. The gaps 32 can all be the same dimension (e.g., gap width
dimension between adjacent rungs 35), all be different dimensions,
or any combination of same and different dimensions from the first
end 33a to the middle region 33c and from the middle region 33c to
the second end 33b. The corners 36 can all be the same
configuration, all be different configurations, or any combination
of same and different configurations from the first end 33a to the
second end 33b. The webs 37 can all be the same dimension, all be
different dimensions, or any combination of same and different
dimensions from the first end 33a to the second end 33b. Changing
the dimension of any of these features, alone or in combination,
can change the electron emission profile, which allows for
selective combinations to tune the electron emission profile.
Additionally, the longitudinal length of each rung may be changed
or optimized in order to obtain a desired temperature profile.
[0121] In one example, the width of all of the outer rungs 35a,
35b, 35n, 35o can be the same dimension, while the rest of the
rungs can all be another different dimension. In one example, the
gaps 32 adjacent to all of the outer rungs 35a, 35b, 35n, 35o can
be the same dimension, while the rest of the gaps 32 can all be
another different dimension. In one example, the corners 36 can
have an apex that is smooth and rounded or sharp and pointed. In
one example, the webs 37 at an outer corner 36 can be a different
dimension from the webs 37 at an inner corner 36.
[0122] For example, the outer rungs 35 can be fabricated so as to
be wider than middle rungs 35 and/or inner rungs 35, thereby
assuring less electrical resistance so as to remain cooler
resulting in lower (or no) emission of electrons. Moreover, the
widths of the gap 32 between adjacent rungs 35 can be adjusted to
compensate for rung width thermal expansion and rung length thermal
expansion, as well as for width and length contraction.
[0123] In one embodiment, the web 37 widths can be used to tune the
resistance in the rungs 35, and thereby the heating and temperature
of each rung 35 due to current passing therethrough can be tuned.
For example, in certain applications the midpoints of the rungs 35
can be heated readily, with the ends at the corners 36 or at the
webs 37 tending to be cooler. Adjusting the dimension of the webs
37 provides a level of control to "tune" the thermionic emission
characteristics of the electron emitter 22. The webs 37 can be
dimensioned such that the temperature of the rung 35 matches a
desired value and is more uniform between corners 36 along the
lengths of each rung 35. This affects the rungs 35 on either side
of the corner 36, so a web 37 can be matched to the two rung
lengths of the rungs 35 that the particular web 37 is between. This
also provides some control over individual rung 35 temperatures so
it is possible to create a temperature profile across the width and
length of the entire electron emitter 22 which can be tailored or
tuned to meet various needs or specific applications. Tuning the
web 37 dimensions can be accomplished by varying the dimension of
the slots 38 that extend from the gaps 32 and terminate in the
corners 36. Tuning web dimensions can be considered a primary
design tool for tuning temperature and electron emission profiles
of the electron emitter 22. Often, the web 37 can be about the same
dimension as the width of the rugs 35, or within 1%, 2%, 4%, 5%, or
10% thereof.
[0124] In one embodiment, the width of one or more of the rungs 35
can be adjusted to tune the temperature profile, which in turn
tunes the electron emission profile; however, this approach can be
considered to be a secondary design tool in terms of achieving
specific temperature and electron emission profiles. In certain
applications, modification of the width of the rungs 35 may not
have as strong of an effect on the temperature profile, and might
tend to heat or cool the entire length of the rung 35. However,
this approach can be used to suppress the emission on the outer
rungs 35a, 35b, 35n, 35o of the electron emitter 22. Dimensioning
the outer rungs 35a, 35b, 35n, 35o to be larger or have a larger
dimension can avoid emission from the outer rungs 35a, 35b, 35n,
35o, where emission from these outer rungs 35a, 35b, 35n, 35o can
create undesirable X-rays that manifest as wings and/or double
peaking in the focal spot. On the other hand, dimensioning the
middle rungs or inner rungs as well as the central rung to be
relatively smaller in dimension can enhance emission from these
rungs 35. As such, dimensioning one or more rungs 35 to be smaller
than one or more other rungs 35 can result in the smaller rungs
having enhanced electron emission compared to the larger rungs.
Thus, any one or more rungs 35, connected or separated, can be
dimensioned to be smaller to increase electron emission or
dimensioned to be larger to inhibit electron emission.
[0125] In certain embodiments, the electron emitter 22 can be
configured with different dimensions of rungs 35, gaps 32, and/or
webs 37 to limit or suppress electron emission from certain rungs
35 of the emitter such that electrons are emitted from different
areas of the emitter at different rates. For example, due to
proximity to other structures at the perimeter of the electron
emitter 22, which may cause the emitted electrons to have an
unwanted trajectory, the outer rungs 35 can have a larger dimension
(e.g., wider) compared to the inner rungs 35 or central rung 35h,
which causes lower temperatures in the outer rungs 35 and thereby
comparatively less electron emission from the outer rungs 35.
Different dimension parameters of the rungs 35, gaps 32, and/or
webs 37 can be used to obtain a smaller electron emission area from
a physically larger electron emitter 22. For example, only the
central rung 35h and adjacent inner rungs 35 may significantly emit
electrons from the electron emitter 22 by tuning the different
dimension parameters. Alternatively, the central rung 35h and/or
inner-most rungs 35 can be dimensioned to be thicker than rungs 35
between these rungs 35 and the outer rungs 35 to create a hollow
beam of electrons. Any one of a different number of emission
profiles can be provided, including non-uniform or non-homogenous
profiles by tuning the dimensional parameters of the rungs, webs,
and gaps of the planar electron emitter 22.
[0126] While the dimensions of the rungs 35, gaps 32, and/or webs
37 is usually considered in the planar dimension that is shown in
FIG. 3B, the orthogonal dimension (e.g., height that is into or out
from the page of FIG. 3B, as shown in FIG. 3C) may also be tuned.
Also, the dimension of the rungs 35, gaps 32, and/or webs 37 being
tuned can be width or height so that the cross-sectional area is
tuned. On the other hand, the height can be set where the width is
tuned so that the planar emitter surface 34 is tuned for electron
emission.
[0127] In one embodiment, relative cooling of rungs 35 in other
positions can be done by making these rungs 35 relatively
cross-dimensionally larger as needed to modify the emission profile
and/or to create other focal spots or multiple focal spots. For
example, as noted, relative cooling (e.g., comparatively reduced
temperature) of the central rung 35h or inner-most rungs (e.g.,
35f, 35g, 35i, 35j, optionally 35p, 35q) of the electron emitter 22
can be done by making these rungs have a larger dimension (e.g.,
wider) compared to the middle rungs (e.g., 35c, 35d, 35e, 35k, 35l,
35m) to create a hollow beam for certain applications. The outer
rungs (e.g., 35a, 35b, 35n, 35o) can be larger than the middle
rungs 35 so that the outer rungs 35 do not substantially emit
electrons. Also, if central rung 35h and the middle rungs 35 are
smaller than the inner-most rungs 35, then a spot in halo electron
emission profile can be generated. If the central rung 35h and
optionally inner-most rungs are smaller than the middle and outer
rungs, then the electron emission can be condensed into the center
of the electron emitter 22. Thus, the dimensions of different rugs
35 can be tailored alone, or with the dimension of the webs 37, for
tuning temperature and electro emission profiles.
[0128] In another embodiment, a variable width down the length of
one or more rungs 35 can provide a tuned temperature and emission
profile. However, such rung 35 dimensioning should be tailored in
view of adjacent rungs 35 across the gaps 32 to avoid larger gaps
32 between rungs 35, which larger gaps 32 can in turn create more
edge emission electrons with non-parallel paths, which is
unfavorable.
[0129] In one embodiment, it can be desirable to dimension the gaps
32 in accordance with the thermal expansion coefficient of the
emitter body material so that a gap 32 always exists between
adjacent rungs 35 while cool and while fully heated. This maintains
the single electrical current path from the first end 33a to the
second end 33b.
[0130] In view of design optimization of the emitter pattern 30 and
dimensions thereof, the following dimensions can be considered to
be example dimensions that can be designed by the design protocols
described herein. The height (e.g., material thickness) of each
rung 35 can be about 0.004'', or about 0.004'' to 0.006'', or about
0.002'' to 0.010''. The rung 35 width can be about 0.0200'', or
about 0.0200'' to 0.0250'', or about 0.0100'' to 0.0350''. The rung
35 width can be determined along with the rung length and rung
thickness so that each rung is designed to match the emitter
supply's available current. The rung 35 length can be about 0.045''
to 0.260'', or about 0.030'' to 0.350'', or about 0.030'' to
0.500'', where the rung 35 length can be dimensioned depending on
the emission area and the resulting emission footprint. The gap 32
width can be about 0.0024'' to 0.0031'', or about 0.002'' to
0.004'', or about 0.001'' to 0.006'', where the gap 32 width can
depend on thermal expansion compensation needed to maintain the
gaps so that the adjacent rungs 35 do not touch. The web 37
dimension can be about 0.0200'' to 0.0215'', or about 0.0200'' to
0.0250'', or about 0.0100'' to 0.0350'', which dimension can be
tied to rung 35 width and the desired heating profile. The result
of the dimensioned emitter 22 is that for a given heating current,
desired emission current (mA), focal spot size, and allowed foot
print, the dimensions of the rung 35, web 37, and gap 32 can be
modified to design an emitter 22 that creates a laminar electron
beam needed for a particular application.
[0131] Additionally, FIG. 3B shows five different number blocks:
R1, R13, R45, R80, and R92, which correspond with the ninety-two
discrete regions of the emitter body 29 from the first end 33a
(e.g., region R1) to the second end 33b (e.g., region R92) shown by
the squares on the rungs 35. Each of these regions were analyzed
for temperature upon being energized by electrical current, which
data is shown and described in FIGS. 5A and 5B and Tables 1 and 2
below.
[0132] FIG. 3C illustrates various cross-sectional profiles 40a-40h
of the rungs 35, where each has a flat emitting surface 41. As
such, the electrons are preferentially emitted from the flat
emitting surface 41, such that all of the flat emitting surfaces 41
of the rungs 35 cooperate to form the planar emitter surface 34.
However, round emitting surfaces (not shown) may be used in some
instances for forming the planar emitting surface 34.
[0133] In yet other embodiments, other general shapes and/or other
cut patterns can be designed to achieve a desired emission profile
for an electron emitter. Various other configurations, shapes, and
patterns can be determined in accordance with the electron emitter
embodiments described herein.
[0134] Also, additional attachments can be made for shortening the
current path or creating adjacent emitters from the same field, for
example. In one example, the attachments can be additional legs
that may or may not be coupled to additional electrical leads. The
attachments can be at any region from region R1 to region R92 (see
FIG. 3B). When coupled to electrical leads, the attachments can
define new electron paths to cause some regions to have current and
others to have no current, which can result in inhomogeneous
temperature and emission profiles. The locations of the attachments
can then provide for custom electron paths and thereby custom
emission patterns. While not shown, additional legs, e.g.,
conductive or non-conductive, could be provided for support to the
electron emitter 22 if needed for a given application. The legs can
be attached at the ends, edges, center, or other locations of the
rungs along the emitter 22 or at any other locations. When
non-conductive, the legs can be attached to any region and provide
support to keep the emitter 22 to have the planar emitter surface
34. When conductive, the legs can be attached to any region to
provide support to keep the emitter 22 to have the planar emitter
surface 34 and to define electron flow paths to customize the
temperature and emission profiles.
[0135] In one embodiment, the gaps 32 between some of the rungs 35
can be dimensioned to be true gaps 32 while cool, but then once
thermal expansion occurs, the gaps 32 shrink so that the adjacent
rungs 35 contact each other to create a new electrical current
path. This can be done to cause the effective dimension to be small
at low temperatures, but then increase at higher temperatures so
that the rungs 35 that touch upon thermal expansion can provide an
effectively larger rung 35 that reduces the local temperature. Such
variable gap 32 dimensions that close upon heating can be designed
so that the electron emitter 22 has a certain temperature and
electron emission profile upon full operation. For example, the gap
32 between outer rungs 35 can close upon heating so that the outer
rungs 35 emit significantly less electrons than the central rungs
35.
[0136] In one embodiment, the design of the electron emitter 22 can
be conducted so that the heating profile of the emitter 22 can be
tailored to meet any desired temperature and emission profile.
Also, each direction across any rung 35, web 37, or gap 32 can be
designed so that the temperature profile of the entire planar
emitting surface can be tailored to produce the overall desired
electron emission profile. Electron emission can be suppressed in
desired regions on the emitter 22 to meet the needs of a given
application. Hollow beams, square, or rectangular beams as well as
specific electron intensity emission distributions can be created
to meet a given imaging need. Modulation Transfer Function (MTF)
responses can also be matched for a desired application, which may
be determined with the beam focusing devices.
[0137] In one embodiment, designs for the layout of the electron
emitter 22 can be scaled to increase emission area to facilitate
higher power imaging applications or to match power levels for
specific applications. That is, select rungs 35 can be relatively
smaller compared to other rungs 35 to determine which rungs 35 will
preferentially emit electrons. In some instances, a large number of
rungs 35 can be dimensionally smaller to increase the emission from
these rungs 35 and thereby increase the size of the emission
stream.
[0138] In one embodiment, the design of the electron emitter 22 to
maintain the planar emitter surface 34 throughout heating and
electron emission can be obtained with the illustrated emitter
pattern 30. The planar nature of the emitter 22 produces electron
paths substantially perpendicular to the emitting surface.
Maintaining relatively small gaps 32 with no windows or apertures
in the emitter pattern 30 can reduce edge or perpendicular electron
emission.
[0139] In one embodiment, the emitter pattern 30 can be as
illustrated in order to have a structural design such that the
emitter 22 is self-supporting in the emitting region (e.g., central
region) thereby eliminating the need for additional support
structures. The emitter pattern of FIG. 3B has been established to
be self-supporting without significant curling, bending or warping
at high temperatures and electron emission.
[0140] In one embodiment, the emitter pattern 30 can be designed
such that the outer portions of the emitter 22 do not emit
electrons (e.g., or not a significant number), thereby decreasing
the effect that any focusing structure has on electrical fields at
the edge of the emitter. Often the focusing structure (e.g., beam
focusing element 11) includes the field shaping component(s) (e.g.,
magnetics) around the outer perimeter of the emission pathway or
throw path. This configuration and reduction of emission from outer
rungs 35 improves the behavior of the electron beam, making it more
laminar as a whole.
[0141] In one aspect, the dimensions of the rungs 35, gaps 32, and
webs 37 can be modulated, designed, or optimized so that the
electrons are not emitted homogenously (i.e., different areas of
the emitter may emit a higher number of electrons than others). The
emitter pattern 30 is shaped and dimensioned to have a particular
resistivity at one or more select locations, which causes different
portions of the emitter 22 to be heated at different temperatures,
and thereby have different emission profiles.
[0142] In one embodiment, the planar emitter described herein can
be utilized in an X-ray tube to emit an electron beam from the
cathode to the anode. The configuration of the planar emitter
results in an inhomogeneous temperature profile from the first end
to the second end and across the entirety of the planar emitter
surface when a current is passed through. The inhomogeneous
temperature profile is a result of the planar emitter pattern with
the rungs, webs, and gap dimensions. Additionally, the description
of the planar emitter provided herein describes the ability to tune
the emitter to obtain different temperature profiles. The
inhomogeneous temperature profile of the planar emitter for a
current results in different regions of the emitter having
different temperatures, which results in the planar emitter
emitting an inhomogeneous electron beam profile. The inhomogeneous
electron beam profile is a result of the inhomogeneous temperature
profile, where regions of different temperature have different
electron emissions. The ability to tailor the temperature profile
allows for tailoring the inhomogeneous electron beam profile, such
as by selectively dimensioning the different features so that some
regions become hotter than others when in operation. Since the
emission is thermionic, different regions of different temperatures
result in different election emissions, and thereby result in the
inhomogeneous electron beam. This principle also allows for one,
two, or more focal spots by having a number of regions with a high
emission temperature and other regions with a low emission
temperature or the other regions may not emit electrons by
thermionic emission. In certain regions, there can be no electrons
emitted or relatively few electrons emitted compared to other
regions. Thus, during operation of a single electron emitter,
certain regions can have enhanced electron emission and others can
have suppressed electron emission to contribute to the
inhomogeneous electron beam profile.
[0143] The planar emitter can inhomogeneously emit electrons in an
electron beam from the substantially planar surface of the emitter
with a reduced lateral energy component.
[0144] The emitter pattern can be designed in such a way by varying
the dimensions of the different rungs, webs, and gaps so that some
regions of the emitter (e.g., outside region or outer rungs in one
example) do not emit electrons or emit a significantly fewer amount
of electrons compared to other regions. This decreases the effect
the focusing elements (see FIG. 2B) have on electrical fields at
the edge of the emitter. The focusing elements are field shaping
components placed about the outer perimeter of the emitter, but
which have reduced focusing effect when the outside rungs of the
emitter do not emit electrons or emit substantially fewer electrons
compared to other regions, such as the middle region. In any event,
tailoring the inhomogeneous temperature profile to tune the
inhomogeneous electron emission profile can improve the behavior of
the inhomogeneous electron beam to become more laminar as a
whole.
[0145] In one embodiment, a method of inhomogeneously emitting
electrons from an electron emitter can include: providing the
electron emitter of claim 1 having a planar emitter surface formed
by the plurality of elongate rungs; and emitting an inhomogeneous
electron beam from the planar emitter surface in a perpendicular
direction.
[0146] FIG. 4 shows an electron emitter 22 that has the emitter
pattern 30 of FIGS. 3A-3B. Select regions of the emitter 22 are
selected for dimension optimization. It should be noted that the
dimensions of one region relative to one end are duplicated in the
corresponding region from the other end, which is shown by the
designations W-1, W-2, W-3, W-4, and W-5 being at multiple
locations, where the dimensions for different designations is
different and the same for some designations.
[0147] As shown in the example emitter 22 of FIG. 4, the distances
of the features are as follows: from A to B is 0.0224 inches; from
A to C is 0.0447 inches; from A to D is 0.0681 inches; from A to E
is 0.1445 inches; from A to F is 0.1679 inches; from A to G is
0.1902 inches; and from A to H is 0.2126 inches; from AA to AB is
0.0231 inches; from AA to AC is 0.0455 inches; from AA to AD is
0.0679 inches; from AA to AE is 0.0912 inches; from AA to AF is
0.1132 inches; from AA to AG is 0.1366 inches; from AA to AH is
0.159 inches; and AA to AI is 0.1813 inches. Gap G1 is 0.0031
inches; gap G2 is 0.0024 inches; and Gaps G3, G4, G5, G6, G7, and
G8 are all 0.0024 inches. The dimensions of the rungs can be
calculated based on the above dimensions. Also, web W-1 is 0.0236
inches and its corresponding slot 38 is 0.0016 inches; web W-2 is
0.0215 inches and its corresponding slot 38 is 0.0016 inches; web
W-3 is 0.0205 inches and its corresponding slot 38 is 0.0016
inches; web W-4 is 0.0204 inches and its corresponding slots 38 are
each 0.0016 inches; and web W-5 is 0.02 inches with its
corresponding slot 38 is 0.0016 inches. Also, the legs 31a, 31b can
be 0.346 inches. From the forgoing dimensions, the emitter pattern
30 can be determined. Also, any of the dimensions described herein,
together or alone, can be modulated by 1%, 2%, 5%, or 10% or
more.
[0148] FIG. 5A illustrates an emitter temperature profile of the
emitter of FIG. 4 for a maximum temperature (Tmax) being 2250
degrees C. with current being 7.75 A, voltage being 8.74 V, and
input power being 67.7 W. Specific region temperatures in Celsius
from region R1 to region R92 (see FIG. 3B for region designations)
are shown in Table 1.
TABLE-US-00001 TABLE 1 Max Temp-2250 (with Emitter Region #
adjusted resistivity) 1 1788.6 2 1892.8 3 1970.7 4 2033.8 5 2080.2
6 2103.7 7 2123.2 8 2146.8 9 2164 10 2176.4 11 2187.5 12 2197.1 13
2204.7 14 2210.2 15 2214.1 16 2217.1 17 2220.2 18 2224.5 19 2224.1
20 2226.4 21 2228.5 22 2229.9 23 2231.4 24 2234.1 25 2238.1 26
2243.4 27 2239.6 28 2238.1 29 2239.1 30 2241.9 31 2246.6 32 2242.3
33 2240.2 34 2240.4 35 2241.4 36 2244.4 37 2248 38 2238.9 39 2236.5
40 2243.2 41 2236.9 42 2237.7 43 2244.4 44 2254.1 45 2254.8 46
2245.8 47 2245.9 48 2254.9 49 2254.3 50 2244.5 51 2237.8 52 2237 53
2243.3 54 2236.6 55 2239 56 2248.1 57 2244.5 58 2241.5 59 2240.5 60
2240.2 61 2242.4 62 2246.7 63 2242 64 2239.1 65 2238.2 66 2239.7 67
2243.5 68 2238.2 69 2234.1 70 2231.4 71 2229.9 72 2228.5 73 2226.4
74 2224 75 2224.4 76 2220.1 77 2217.1 78 2214 79 2210.2 80 2204.6
81 2197 82 2187.5 83 2176.3 84 2164 85 2146.7 86 2123.1 87 2103.6
88 2080.1 89 2033.7 90 1970.5 91 1892.6 92 1788.3
[0149] FIG. 5B illustrates an emitter temperature profile of the
emitter of FIG. 4 for a maximum temperature (Tmax) being 2350
degrees C. with current being 8.25 A, voltage being 9.7 V, and
input power being 80 W. Specific region temperatures in Celsius
from region R1 to region R92 (see FIG. 3B for region designations)
are shown in Table 2.
TABLE-US-00002 TABLE 2 Max Temp-2350 (with Emitter Region #
adjusted resistivity) 1 1871.1 2 1981.7 3 2063.1 4 2128.1 5 2175.1
6 2198.7 7 2218 8 2241.1 9 2257.6 10 2269.4 11 2280.1 12 2289.5 13
2297.1 14 2302.6 15 2306.4 16 2309.4 17 2312.5 18 2317.4 19 2316.4
20 2318.8 21 2321 22 2322.5 23 2324.1 24 2327.1 25 2331.7 26 2337.8
27 2333.3 28 2331.5 29 2332.6 30 2335.9 31 2341.4 32 2336.3 33
2333.8 34 2334.2 35 2335.3 36 2338.9 37 2343.2 38 2332.6 39 2329.9
40 2337.7 41 2330.3 42 2331.1 43 2338.8 44 2350.1 45 2350.8 46
2340.3 47 2340.3 48 2350.9 49 2350.3 50 2339 51 2331.2 52 2330.4 53
2337.9 54 2330 55 2332.7 56 2343.3 57 2339 58 2335.4 59 2334.2 60
2333.9 61 2336.4 62 2341.4 63 2335.9 64 2332.6 65 2331.5 66 2333.4
67 2337.9 68 2331.8 69 2327.2 70 2324.2 71 2322.5 72 2321 73 2318.7
74 2316.3 75 2317.3 76 2312.5 77 2309.3 78 2306.3 79 2302.5 80 2297
81 2289.4 82 2280 83 2269.3 84 2257.5 85 2241 86 2217.9 87 2198.6
88 2175 89 2127.9 90 2063 91 1981.5 92 1870.8
[0150] FIG. 6A shows a corner 36 having cutouts 60 at the location
of the web 37. The cutouts 60 change the relative dimension of the
web 37, which can be tuned in accordance with the rungs 35 adjacent
to the corner. The dimension of these cutouts 60 can be used for
resistance matching and modulation, where the size of the cutouts
60, or placement thereof, or number thereof (e.g., one, two, or
three or more cutouts at a web 37) can be used to tune the
resistivity of a rung 35.
[0151] FIG. 6B shows the corner 36 having an apex slot 62 and a
cutout 60, and shows the rungs 35 having various cutouts 60 in
various shapes and dimensions. The cutouts of the rungs and at
corners can vary. The cutouts can be uniform in dimension; however,
they may also be non-uniform. The cutouts at a gap can also have
non-uniform openings to the gap. A rung can also include a long,
tapering cut running the length of the rung. Thus, the cutouts
illustrated can be of any dimension relative to the rungs.
[0152] In one embodiment, an electron emitter can include: a
plurality of elongate rungs connected together end to end from a
first emitter end to a second emitter end in a plane so as to form
a planar pattern, each elongate rung having a rung width dimension;
a plurality of corners, wherein each elongate rung is connected to
another elongate rung through a corner of the plurality of corners,
each corner having a corner apex and an opposite corner nadir
between the connected elongate rungs of the plurality of elongate
rungs; a first gap between adjacent non-connected elongate rungs of
the plurality of elongate rungs, wherein the first gap extends from
the first emitter end to a middle rung; a second gap between
adjacent non-connected elongate rungs of the plurality of elongate
rungs, wherein the second gap extends from the second emitter end
to the middle rung, wherein the first gap does not intersect the
second gap; and one or more cutouts at one or more of the corners
of the plurality of corners between the corner apex and corner
nadir or at the corner nadir.
[0153] In one embodiment, one or more body portions of each corner
between the corner apex and corner nadir, excluding the one or more
cutouts, together define a web dimension between the corner apex
and corner nadir, wherein the web dimension is within 10% of the
rung width dimensions of the connected elongate rungs at the
corner.
[0154] In one embodiment, from the first end to middle rung, the
first gap has a plurality of first gap segments each having a gap
segment width, each gap segment width having a dimension that
maintains the first gap when the emitter is at a non-emitting
temperature and at an electron emitting temperature, and wherein
from the second end to middle rung, the second gap has a plurality
of second gap segments each having a gap segment width, each gap
segment width having a dimension that maintains the second gap when
the emitter is at the non-emitting temperature and at the electron
emitting temperature.
[0155] In one embodiment, the first gap is either clockwise or
counter clockwise from the first rung to the middle rung, and the
second gap is the other of clockwise or counter clockwise from the
middle rung to the second end so as to be the opposite orientation
of the first gap.
[0156] In one embodiment, a first portion of the plurality of
elongate rungs has a first rung width dimension and a second
portion of the plurality of elongate rungs has at least a different
second rung dimension.
[0157] In one embodiment, two or more of the first gap segments
have different gap segment width dimensions, and two or more of the
second gap segments have different gap segment width
dimensions.
[0158] In one embodiment, first and second rungs from the first
emitter end have a first rung width dimension, and other rungs from
the second rung to the middle rung have at least one rung width
dimension different from the first rung width dimension. Also,
ultimate and penultimate rungs from the second emitter end have the
first rung width dimension, and other rungs from the penultimate
rung to the middle rung have at least one rung width dimension
different from the first rung width dimension.
[0159] In one embodiment, each elongate rung of the plurality of
elongate rungs has a flat surface that together the flat surfaces
form a planar emitting surface in the form of the planar
pattern.
[0160] In one embodiment, a first elongate leg can be coupled to a
first elongate rung at the first end, and a second elongate leg can
be coupled to an ultimate elongate rung at the second end. Also,
the first elongate leg and second elongate leg can be at an angle
relative to the planar emitting surface.
[0161] In one embodiment, the present technology can include a
design protocol to design a planar emitter pattern, which design
includes particular dimensions for the emitter pattern. The design
can include the particular emitter pattern 30 shown in FIG. 3B. The
design protocol can include determining a desired temperature
profile or desired emission profile, and determining dimensions for
particular rungs, webs, and/or gaps to achieve the desired profile.
These determinations can be performed by a user inputting data
input into a computing system and simulating a temperature profile
on the computer based on the input. The designing of the dimensions
can be performed on a computer, such as a CAD program, based on
data input by a user into the computer. The design can then be
simulated on a computer to determine whether or not the simulation
produces the desired temperature profile. The simulation can be
conducted based on instructions input into the computer by the
user. The simulated temperature profile obtained by the computer
can be indicative of the electron emission profile, which allows
for computer CAD design and temperature simulation. Once a desired
temperature profile can be designed and simulated on the computer
by the user, a real electron emitter can be manufactured and tested
for the real temperature profile and/or electron emission profile.
Once tested, the data for the real emitter can then be input by the
user into the computer and used to modulate dimensions of the
rungs, webs, and/or gaps in another computer CAD model, and then
the new emitter design can be simulated on the computer, and then
manufactured and tested. The CAD design operated by the user based
on user input into the computer can include: determining a rung
dimension for each rung; determining a web dimension for each web;
and determining a gap dimension for each gap. Here, one or more of
these different features can have the same dimension, and one or
more of the same features can have different dimensions. That is,
some rungs can have the same dimension and some can have different
dimensions, some gaps can have the same dimension and some can have
different dimensions, and some webs can have the same dimension and
some can have different dimensions.
[0162] An example of a design method can include the following
steps of a design protocol to design a planar emitter. Any of these
steps can be implemented by a user inputting data input into the
computer and inputting instructions into the computer to cause the
computer to perform computational calculations and simulations. In
a first step, a particular application for an X-ray is determined.
The particular application that is determined can result in a
particular X-ray emission pattern or focal spot shape or number of
focal spots to be identified. As such, the desired emission profile
is determined based on the particular application. In a second
step, an initial pattern shape for the emitter pattern can be
determined. Here, the pattern shape can be the emitter pattern that
is illustrated herein, which includes a number of rungs connected
together at 90 degree corners to start from a first end and end at
a second end, where each corner can have a web. In a third step,
the desired emission profile can be matched or overlaid on the
emitter pattern so that the rungs to be configured for electron
emission match the emission profile and so that the rungs to be
configured to have a reduced emission or no emission can match the
areas of no emission in the emission profile. In the fourth step,
the rungs to emit electrons for the emission profile can be
identified, and rungs to not emit substantial electrons can be
identified. This results in a general primer for the dimensions of
the emitter pattern. In a fifth step, the length and width
dimensions of each of the rungs can be determined to match the
emitter pattern to the emission profile. In a sixth step, the gap
dimensions can be determined for each gap between rungs, which
dimensions can be determined in view of the thermal expansion
coefficient so that the gaps exist while cool and while fully
heated and emitting electrons. In a seventh step, the emitter
pattern having the rung and gap dimensions can be overlaid or
otherwise compared with the desired emission profile, and any
adjustments can be made so that the emitter pattern is capable of
emitting the emission profile. In an eighth step, the web
dimensions can be determined to correspond with the rung widths in
order to obtain a rung temperature potential. The web dimensions
are often adjusted to be about the dimension of the rung width,
such as within 1%, 2%, or up to 5% or up to 10%. Based on the
outcome from these steps, the planar emitter profile can be
designed with the appropriate dimensions on a computer-assisted
design program on a computer. The planar emitter pattern with
dimensions can be saved as data in a database on a data storage
medium of the computer. However, any of these steps may be
optional.
[0163] Once designed, the planar emitter pattern with dimensions
can be processed through a simulation protocol on a computer. Such
processing can be implemented by a user inputting parameters and
input into the computer. The simulation protocol can be part of the
design method. The simulation can simulate the temperature for each
of the rungs based on the planar emitter pattern with one or more
electrical current profiles, which can be input into the computer.
That is, the electrical current that is passed through the planar
emitter can be simulated with various parameters that can be
varied. Accordingly, the planar emitter pattern can be simulated
with one or more electrical current profiles to determine the
temperature profile for the entire emitter, each rung, and regions
(e.g., see FIG. 3B and Tables 1 and 2). The temperature profile for
the entire emitter, each rung, and/or regions can be saved as data
in a database on the computer.
[0164] Once one or more temperature profiles for the emitter are
determined from the simulation, an iteration protocol can be
performed on the computer based on input from the user so that any
of the dimensions of any of the webs, rung widths, and/or gap
dimensions can be modulated in a manner so that the iterative
emitter pattern is likely to provide a temperature profile that
matches the desired temperature profile. The iteration protocol can
include the design protocol and simulation protocol, which
iteration protocol can be repeated by the user with the computer
until the emitter pattern provides a suitable temperature
profile.
[0165] Once the emitter pattern is simulated to provide a suitable
temperature profile, a physical planar electron emitter can be
fabricated to include the emitter pattern and appropriate
dimensions for the webs, rung widths, and/or gaps. The fabrication
can be part of a method of manufacture. Generally, a piece of flat
material having an appropriate thickness (e.g., height) can be
laser-cut into the emitter pattern having the appropriate
dimensions for the webs, rung widths, and gaps.
[0166] Once the physical emitter has been manufactured, it can be
tested with one or more electrical currents in order to determine
the temperature profile for each of the temperatures. The real
temperature profile that is measured can identify the temperature
for the entire emitter, each rung, and/or regions. The real
temperature profile for the entire emitter, each rung, and/or
regions for one or more current profiles can be input into the
computer based on instructions obtained by the user and saved as
data in a database on the computer. This temperature data can be
linked with the emitter pattern and dimension data so that the
emitter pattern and dimensions can be recalled when the
corresponding temperature profile is desired. That is, a user can
input instructions into the computer in order to obtain the emitter
pattern and dimension data from the database. Thus, the database
can include a plurality of emitter pattern and dimension designs
linked to the temperature profiles for one or more current
profiles. This allows a temperature profile to be selected by the
user based on input from the user into the computer, and then the
emitter pattern and dimensions for that temperature profile to be
obtained from the database and provided to the user.
[0167] The database can serve as a repository of temperature
profiles and corresponding emitter patterns and dimensions. This
allows for the design of a certain emitter pattern for a
temperature profile to start with an emitter pattern design with a
known temperature profile, and then the parameters can be varied in
a manner to iterate toward the desired temperature profile. If a
desired temperature profile has already been determined, then the
corresponding emitter pattern and dimensions can be selected from
the database by the user.
[0168] In one embodiment, a method of manufacturing a planar
electron emitter can include: obtaining a designed pattern, which
can be computer designed and simulated; obtaining a sheet of
material; and laser cutting the emitter pattern into the sheet. The
legs can then be bent from the planar emitter pattern. In one
example, once the shape of the pattern has been made, it can be
recrystallized and set.
[0169] In one embodiment, a method of designing an electron emitter
can include: determining a desired cross-sectional profile of an
electron emission from an electron emitter, where the parameters of
the electron emitter can be input into a computer; determining a
desired temperature profile for the electron emitter that emits the
desired cross-sectional profile; and determining desired emitter
dimensions for a defined electrical current through the electron
emitter that produces the desired temperature profile, which can be
determined through simulations run on the computer under
instructions input by the user. The emitter dimensions can include:
each rung width dimension; each first gap segment dimension; each
second gap segment dimension; and each web dimension. The electron
emitter can include: a plurality of elongate rungs connected
together end to end at corners, each corner having a corner apex
and an opposite corner nadir, each elongate rung having a rung
width dimension; a first gap between adjacent non-connected
elongate rungs from the first emitter end to a middle rung, the
first gap including a plurality of first gap segments each having a
first gap segment width; a second gap between adjacent
non-connected elongate rungs from the second emitter end to the
middle rung, the second gap including a plurality of second gap
segments each having a second gap segment width; and one or more
body portions of each corner between the corner apex and corner
nadir together define a web dimension for each corner.
[0170] In one embodiment, the method can include: inputting an
emitter pattern of the electron emitter into a computer by the
user, the emitter pattern including the emitter dimensions;
simulating the temperature profile of the emitter pattern on the
computer for the defined current based on input from the user; and
determining whether the emitter pattern has the desired temperature
profile for the defined electrical current.
[0171] In one embodiment, the method can include: (a) changing one
or more of the emitter dimensions in the computer by the user to
obtain an iterative emitter pattern having iterative emitter
dimensions; and (b) simulating the temperature profile of the
iterative emitter pattern on the computer for the defined current
based on input from the user; and (c) determining whether the
iterative emitter pattern has the desired temperature profile for
the defined electrical current, if not, then repeating (a) through
(c).
[0172] In one embodiment, the method can include: setting the web
rung dimensions to correspond with an emitter pattern; and varying
the web dimensions to obtain the desired temperature profile. These
actions can be performed with the computer based on input into the
computer by the user.
[0173] In one embodiment, the method can include: setting the web
rung dimensions to correspond with an emitter pattern; varying the
web dimensions to obtain a first temperature profile that is
different from the desired temperature profile; and varying the
rung width dimensions after varying the web dimensions to obtain
the desired temperature profile. These actions can be performed
with the computer based on input into the computer by the user.
[0174] In one embodiment, the method can include: setting emitter
dimensions for each rung width dimension, each first gap segment
dimension, and each second gap segment dimension; and varying each
web dimension to obtain the desired temperature profile. These
actions can be performed with the computer based on input into the
computer by the user.
[0175] In one embodiment, the method can include: obtaining a
simulated temperature profile that corresponds to the desired
temperature profile; manufacturing a physical electron emitter
having the emitter pattern that produced the simulated temperature
profile; testing the physical electron emitter with a defined
electrical current; and measuring the temperature profile of the
physical electron emitter.
[0176] In one embodiment, when the temperature profile of the
physical electron emitter matches the desired temperature profile,
the physical electron emitter is implemented in an X-ray tube.
Alternatively, when the temperature profile of the physical
electron emitter does not match the desired temperature profile,
the method further comprises: (a) changing one or more of the
emitter dimensions to obtain an iterative emitter pattern having
iterative emitter dimensions; and (b) simulating the temperature
profile of the iterative emitter pattern on the computer for the
defined current; and (c) determining whether the iterative emitter
pattern has the desired temperature profile for the defined
electrical current, if not, then repeating (a) through (c). The
changes and simulation can be based on input into the computer by
the user.
[0177] In one embodiment, the method can include: obtaining a
plurality of temperature points of the desired temperature profile,
and entering the data thereof into the computer system by the user;
simulating the temperature profile of the emitter pattern on the
computer for the defined current to obtain a plurality of simulated
temperature points of the simulated temperature profile, which can
be performed based on input into the computer by the user;
comparing the plurality of temperature points with the plurality of
simulated temperature points; and selecting the emitter pattern
when the plurality of temperature points substantially match the
plurality of simulated temperature points.
[0178] In one embodiment, a method of manufacturing an electron
emitter can include: obtaining a sheet of electron emitter
material; obtaining an electron emitter pattern; and laser cutting
the electron emitter pattern into the electron emitter material.
The electron emitter pattern can include: a plurality of elongate
rungs connected together end to end from a first emitter end to a
second emitter end in a plane so as to form a planar pattern, each
elongate rung having a rung width dimension; a plurality of
corners, wherein each elongate rung is connected to another
elongate rung through a corner of the plurality of corners, each
corner having a corner apex and an opposite corner nadir between
the connected elongate rungs of the plurality of elongate rungs; a
first gap between adjacent non-connected elongate rungs of the
plurality of elongate rungs, wherein the first gap extends from the
first emitter end to a middle rung; a second gap between adjacent
non-connected elongate rungs of the plurality of elongate rungs,
wherein the second gap extends from the second emitter end to the
middle rung, wherein the first gap does not intersect the second
gap; and one or more cutouts at one or more of the corners of the
plurality of corners between the corner apex and corner nadir or at
the corner nadir. In one aspect, the method can further include
determining that the electron emitter pattern produces a desired
temperature profile for a defined electrical current.
[0179] One skilled in the art will appreciate that, for this and
other processes and methods disclosed herein, the functions
performed in the processes and methods may be implemented in
differing order. Furthermore, the outlined steps and operations are
only provided as examples, and some of the steps and operations may
be optional, combined into fewer steps and operations, or expanded
into additional steps and operations without detracting from the
essence of the disclosed embodiments.
III. Example Embodiments of a Magnetic System providing Electron
Beam Focusing and Two-Axis Beam Steering via Two Quadrupoles
[0180] As noted above, certain embodiments include an electron beam
manipulation component that allows for steering and/or focusing of
the electron beam so as to control the position and/or size and
shape of the focal spot on the anode target. In one embodiment,
this manipulation is provided by way of a magnetic system
implemented as two magnetic quadrupoles disposed in the electron
beam path. For example, in one embodiment, two quadrupoles are used
to provide both steering and focusing of the electron beam. In this
approach, focusing magnetic fields can be provided by both
quadrupoles (e.g., the anode side quadrupole and the cathode side
quadrupole with constant current in the coils) and the electron
beam steering magnetic fields can be provided by one of the
quadrupoles (e.g., the anode side quadrupole or cathode side
quadrupole) that is operated with AC offset for one coil, one pair,
three coils, or two pairs of opposing coils. Alternatively,
magnetic fields for steering can be done for one direction with one
quadrupole having d a single coil or an opposing pair of coils with
AC offset and for the other direction with the other quadrupole
having a single coil or an opposing pair of coils with AC offset,
where the two pairs with AC offset are orthogonal or perpendicular.
The steering can be performed by providing the offset to one coil,
a pair of coils, three coils, or all four coils. When a single coil
has the offset, then the movement of the beam can be diagonal. In
this way, combined beam focusing and steering can be provided using
only quadrupoles. This particular approach can use two quadrupoles
that are each configured for focusing and one of the quadrupoles is
configured for steering.
[0181] The magnetic system 180 of FIG. 1D can include a focusing
quadrupole core 184 and steering quadrupole core 182 (e.g.,
configured to have at least one coil or pair of opposing coils
having AC offset) so as to impose magnetic forces on the electron
beam 112 so as to focus and/or steer the beam. The combination of
the two quadrupole cores 182, 184 are configured to (a) focus in
both directions perpendicular to the beam path, and (b) to steer
the beam in both directions perpendicular to the beam path. In this
way, the two quadrupole cores 182, 184 act together to form a
magnetic lens (sometimes referred to as a "doublet"), and the
focusing and steering is accomplished as the electron beam passes
through the quadrupole "lens." The "focusing" provides a desired
focal spot shape and size, and the "steering" affects the
positioning of the focal spot on the anode target surface 128.
[0182] FIGS. 7A-7B show an example of a combination of an anode
quadrupole core 202 (e.g., also 182) and a cathode quadrupole core
204 (e.g., also 184). Each quadrupole is implemented with a core
section, or a yoke, denoted as a cathode quadrupole yoke at 204a
for the cathode core 204, and an anode quadrupole yoke at 202a for
the anode core 202.
[0183] FIG. 7A shows an embodiment of an anode quadrupole core 202
(e.g., closer to anode) having an anode quadrupole yoke 202a, and
FIG. 7B shows an embodiment of a cathode quadrupole core 204 (e.g.,
closer to cathode) having a cathode quadrupole yoke 204a. Each
quadrupole yoke 202a, 204a includes four pole projections arranged
in an opposing relationship, cathode pole projections 214a,b (e.g.,
first cathode pole projections) and 216a,b (e.g., second cathode
pole projections) on the cathode yoke 204a, and anode pole
projections 222a,b (e.g., first anode pole projections) and 224a,b
(e.g., second anode pole projections) on the anode yoke 202a. Each
quadrupole pole projection includes corresponding quadrupole
electromagnetic coils, denoted as cathode quadrupole coils 206a,b
(e.g., first cathode quadrupole coils) and 208a,b (e.g., second
cathode quadrupole coils) on the cathode yoke 204a and anode
quadrupole coils 210a,b (e.g., first anode quadrupole coils) and
212a,b (e.g., second anode quadrupole coils) on the anode yoke
202a. Current is supplied to the quadrupole coils so as to provide
the desired magnetic focusing (e.g., constant current) and/or
steering (AC offset) effect, as will be described in further detail
below.
[0184] In this context, in conjunction with the embodiments shown
in FIGS. 1A-1D and 7A-7B, reference is further made to FIGS. 8A and
8B. FIG. 8A shows an embodiment of a cathode core 204 having a
cathode yoke 204a and is configured as a quadrupole (e.g.,
cathode-side magnetic quadrupole 204), and FIG. 8B illustrates an
embodiment of an anode core 202 having an anode yoke 202a, also
configured as a quadrupole (e.g., anode-side magnetic quadrupole
202). As previously described in connection to FIGS. 7A-7B, in this
example each core section includes a yoke having four pole
projections arranged in an evenly distributed and opposing
relationship, pole projections 214a,b and 216a,b on the cathode
yoke 204a, and pole projections 222a,b and 224a,b on the anode yoke
202a. Each pole projection includes corresponding quadrupole coils,
denoted at 206a,b and 208a,b on the cathode core 204 and 212a,b and
210a,b on the anode core 202. While illustrated as having a
substantially circular shape, it will be appreciated that each of
the core (or yoke) portions 202a, 204a can also be configured with
different shapes, such as a square orientation, semi-circular,
oval, or other.
[0185] The two magnetic quadrupole cores 202, 204 act as lenses,
and may be arranged so that the corresponding electromagnets
thereof are in parallel with respect to each other, and
perpendicular to the optical axis defined by the electron beam 112.
The quadrupole cores together deflect the accelerated electrons
such that the electron beam 112 is focused in a manner that
provides a focal spot with a desired shape and size. Each
quadrupole lens creates a magnetic field having a gradient, where
the magnetic field intensity differs within the magnetic field. The
gradient is such that the magnetic quadrupole field focuses the
electron beam in a first direction and defocuses in a second
direction that is perpendicular to the first direction. The two
quadrupoles can be arranged such that their respective magnetic
field gradients are rotated about 90.degree. with respect to each
other. As the electron beam traverses the quadrupoles, it is
focused to an elongated spot having a length to width ratio of a
desired proportion. As such, the magnetic fields of the two
quadrupole lenses can have symmetry with respect to the optical
axis or with respect to a plane through the optical axis.
[0186] With continued reference to the figures, the double magnetic
quadrupole includes an anode quadrupole core, generally designated
at 202 and a cathode quadrupole core, generally designated at 204,
that are together positioned approximately between the cathode and
the target anode and disposed around the neck portion 124a as
previously described. The anode quadrupole core 202 in one option
can be further configured to provide AC offset to one coil, a pair
of coils, three coils, or two pairs of opposing coils that enables
a shifting of the focal spot in a plane perpendicular to an optical
axis correspondent to electron beam 112 of the X-ray tube 100 In an
example embodiment, the cathode quadrupole core 204 focuses in a
length direction, and defocuses in width direction of the focal
spot. The electron beam is then focused in width direction and
defocused in length direction by the following anode quadrupole
core 202. In combination the two sequentially arranged magnetic
quadrupoles ensure a net focusing effect in both directions of the
focal spot. However, the focusing and defocusing axes of the two
different cores can be switched between the anode quadrupole core
202 and cathode quadrupole core 204.
[0187] With continued reference to FIG. 8A, a top view of a cathode
quadrupole core 204 is shown. A circular core or yoke portion,
denoted at 204a is provided, which includes four pole projections
214a, 214b, 216a, 216b that are directed toward the center of the
circular yoke 204a. In an example implementation, the yoke 204a and
the pole projections 214a, 214b, 216a, 216b are constructed of core
iron. Moreover, each coil can be comprised of 22 gauge magnet wire
at 60 turns; obviously other configurations can be suitable
depending on the needs of a particular application.
[0188] As is further shown in FIG. 8A, the illustrated example
includes a Focus Power Supply 275 for providing a predetermined
constant current to the four coils, which are connected in
electrical series, as denoted schematically at 250, 250a, 250b
250c, and 250d. In this embodiment, the current supplied is
configured so that the coil has substantially constant current, and
results in a current flow within each coil as denoted by the letter
`I` and corresponding arrow, in turn resulting in a magnetic field
schematically denoted at 260. The magnitude of the current is
selected so as to provide a desired magnetic field that results in
a desired focusing effect. See FIG. 11A, which shows focusing of
the focal spot.
[0189] Reference is next made to FIG. 8B, which illustrates an
example of a top view of an anode quadrupole core 202 having a
circular core or yoke 202a, which includes four pole projections
222a, 222b, 224a, 224b also directed toward the center of the
circular yoke 202a. The anode quadrupole core 202 and four pole
projections 222a, 222b, 224a, 224b can be comprised of a low loss
ferrite material so as to better respond to steering frequencies
(described herein). The coils can utilize similar gauge magnet wire
and similar turn ratio, with variations depending on the needs of a
given application. In one option, if steering frequency is
sufficiently low, then iron can be used in the steering core
instead of ferrite.
[0190] As is further shown in the example embodiment of FIG. 8B,
and in contrast with the cathode quadrupole core 204, each of the
coils of the anode quadrupole core 202 includes a separate and
independent power source for providing current to induce a magnetic
field in a respective coil, each power supply being denoted at 280
(Power Supply A), 282 (Power Supply B), 284 (Power Supply C) and
286 (Power Supply D). For purposes of providing a quadrupole
magnetic field, a constant current (e.g., DC) `Focus Current` is
provided in each of the coils, as denoted by the schematic
electrical circuit associated with each supply (e.g., 281, 283,
285, 287). Accordingly, any current can be provided that results in
substantially constant current in the coils. Moreover, as denoted
by current flow directional arrows at `I` and corresponding arrow,
in turn resulting in a magnetic field schematically denoted at 261.
The focus current in the anode quadrupole core 202 is opposite to
the cathode quadrupole core 204 focus current so as to provide for
complimentary magnetic fields, and thereby the focusing effect.
[0191] As previously discussed, the anode quadruple core 202 is
further configured to receive AC offset in addition to the constant
current in each of the coils. To do so, each of the coils is
provided with--in addition to the constant focus current described
above--an X AC offset current and a Y AC offset current. However,
the AC offset can be zero for one or more coils so long as at least
one coil has an AC offset that imparts steering. The duration of
the AC offset currents are at a predetermined frequency and the
respective offset current magnitudes are designed to achieve an
offset or shifting of the center of the quadrupole field from the
central axis, in turn, a resultant shift in the electron beam (and
focal spot) from a central axis of the cores. Thus, each coil is
driven independently, with a constant focus current, and
perturbations are created in the magnetic field at the desired
focal spot steering frequency by application of desired X offset
and Y offset AC currents in corresponding coils or coil pairs
(e.g., opposing coils) of the anode quadrupole core 202. This
effectively moves the center of the quadrupole magnetic field in
the `x` and/or `y` direction (see, for example, FIGS. 11B and 11C,
which show a representative steering effect), which in turn results
in a shifting of the electron beam (and resultant position of the
focal spot on the anode target) in a prescribed `x` and/or `y`
direction.
[0192] Reference is next made to FIG. 9, which illustrates a
functional diagram illustrating an embodiment of a magnetic control
system for controlling the operation of the quadrupole system of
FIGS. 8A-8B. At a high level, the magnetic control system of FIG. 9
provides the requisite control of coil currents supplied to the
quadrupole cores 202 and 204 so as to (1) provide a requisite
quadrupole field so as to achieve a desired focus of the focal
spot; and (2) provide a requisite shift in the quadrupole field(s)
so as to achieve a desired position of the focal spot. As noted,
control of the coil currents is accomplished in a manner so as to
achieve a desired steering frequency.
[0193] The embodiment of FIG. 9 includes a Command Processing
device 276, which may be implemented with any appropriate
programmable device, such as a microprocessor or microcontroller,
or equivalent electronics. The Command Processing device 276
controls, for example, the operation of each of the independent
power supplies (i.e., which provide corresponding coils operating
current to create a magnetic field), preferably in accordance with
parameters stored in non-volatile memory, such as that denoted at
Command Inputs 290. For example, in an example operational scheme,
parameters stored/defined in Command Inputs 290 might include one
or more of the following parameters relevant to the focusing and
steering of the focal spot: Tube Current (a numeric value
identifying the operational magnitude of the tube current, in
milliamps); Focal Spot L/S (such as `large` or `small` focal spot
size); Start/Stop Sync (identifying when to power on and power off
focusing); Tube Voltage (specifying tube operating voltage, in
kilovolts); Focal Spot Steering Pattern (for example, a numeric
value indicating a predefined steering pattern for the focal spot);
and Data System Sync (to sync an X-ray beam pattern with a
corresponding imaging system).
[0194] In an exemplary implementation, Command Inputs 290 can
correspond to requisite values in a look-up table arrangement.
Focus Power Supply 275 supplies constant focus current to the coils
of the cathode quadrupole core 204 described above. Similarly,
Power Supply A (280), Power Supply B (282), Power Supply C (284)
and Power Supply D (286) supply constant focus current to the
corresponding coils of the anode quadrupole core 202 the focusing
component of each coil, and a AC offset current for purposes of
shifting the focal spot.
[0195] Thus, by way of one example, a Focal Spot size specified as
`small` can cause the Command Processing unit 276 to control the
Focus Power Supply 275 to provide a constant focus current having
the prescribed magnitude (corresponding to a `small` focal spot) to
each of the coils (206a, 208a, 206b, 208b) of the cathode magnetic
quadrupole core 204, as described above. Similarly, each of the
Power Supplies 280 (coil 210a), 282 (coil 212b), 284 (coil 210b),
and 286 (coil 212a) can also be controlled to provide a constant
focus current, having the same magnitude as supplied by Focus Power
Supply 275, to each of the coils of the anode quadrupole core 202.
Again, this can result in a quadrupole magnetic field that imposes
focusing forces on the electron beam so as to result in a `small`
focal spot on the anode target.
[0196] Similarly, a FS Steering Pattern might prescribe a specific
focal spot steering frequency and requisite displacement in an `x`
and/or `y` direction. This can result in Command Processing unit
276 to control each of the Power Supplies 280, 282, 284, and 286 to
supply a requisite X-offset and Y-offset AC current magnitudes to
the corresponding coils (e.g., one coil, a pair of opposing coils,
three coils, or two pairs of opposing coils) of the anode
quadrupole core 202, thereby creating a desired steering effect, in
addition to the beam (focal spot) focus, as described above.
[0197] In an example embodiment, each of the Power Supplies 275,
280, 282, 284 and 286 are high-speed switching supplies, and which
receive electrical power from a main power supply denoted at 292.
Magnetic Control Status 294 receives status information pertaining
to the operation of the power supplies and the coils, and may be
monitored by command processing unit 276 and/or an external monitor
control apparatus (not shown).
[0198] Thus, in the embodiment of FIGS. 8A-8B and FIG. 9, a
magnetic system providing electron beam focusing and two-axis beam
steering via two quadrupoles is provided. While an example
embodiment is shown, it will be appreciated that alternate
approaches are contemplated. For example, while steering of the
electron beam is provided by way of AC offset to one coil or a coil
pair or three coils or two pairs of opposing coils on the anode
quadrupole core 202, it will be appreciated that both the anode
core 202 and the cathode core 204 might be constructed of a ferrite
material, and the steering could be "split" between the cores, each
providing a steering effect, one `x` and one `y` direction for
example. Other variations can also be contemplated, such as both
the cathode core and anode core implementing focusing and
steering.
[0199] Reference is next made to FIG. 10, which illustrates one
example of a methodology 240 for operating the magnetic control
functionality denoted in FIG. 9. Beginning at step 241, a user may
select or identify appropriate operating parameters, which are
stored as command inputs in memory of Command Inputs 290. At step
242, the operating parameters are forwarded to the tube control
unit, which includes command processing unit 276. For each
operating parameter, at step 243 the command processing unit 276
queries a lookup/calibration table for corresponding values, e.g.,
cathode quadrupole constant focus current, anode quadrupole
constant focus current and AC offsets. At step 244, coils are
powered on with respective current values, and confirmation is
provided to the user. At step 245, the user initiates the exposure
and X-ray imaging commences. At completion, step 246, a command is
forwarded which causes power to the coils to be ceased.
[0200] Accordingly, the offset can be applied to one coil or two
opposing coils. In one example, AC offset is only applied to one
coil to get steering in a diagonal direction. In another example,
AC offset can be applied to both coils of an opposing coil pair. In
one example, one coil of an opposing pair receives AC offset, and
the other coil of the opposing pair can be set at zero AC offset.
As such one coil can have AC offset in one coil set to zero and the
other opposing coil of the pair has an AC offset that is not zero.
In one embodiment, the coils of an opposing coil pair can have
different offsets. In one embodiment, the AC offset in a pair of
opposing coils can be created by having one coil with zero offset
while the other has some offset. Application of AC offset to only
one coil or having the coils of a coil pair with different AC
offset can be applied to all embodiments.
[0201] FIG. 12A shows an embodiment of a cathode core 204 having a
cathode yoke 204a and is configured as a quadrupole (e.g.,
cathode-side magnetic quadrupole 204) for focusing with a pair of
coils having AC offset to implement steering, and FIG. 12B
illustrates an embodiment of an anode core 202 having an anode yoke
202a, also configured as a quadrupole (e.g., anode-side magnetic
quadrupole 202) for focusing with a pair of coils having AC offset
to implement steering. The steering of cathode core 204 is
orthogonal to steering of anode core 202. The subject matter of
FIG. 12A can include aspects of FIG. 8A, and the subject matter of
FIG. 12B can include aspects of FIG. 8B as described herein.
[0202] As is further shown in FIG. 12A, the illustrated example
includes a Focus Power Supply 275a for providing a predetermined
constant focusing current to two of the four coils (e.g., 206a and
206b), which are connected in electrical series, as denoted
schematically at 251, 251a, and 251b. Additionally, two of the
coils (e.g., 208a and 208b) include separate and independent power
sources for providing current to induce a magnetic field in a
respective coil, each power supply being denoted at 280 (Power
Supply A) and 284 (Power Supply C). For purposes of providing a
quadrupole magnetic field, a constant DC `Focus Current` is
provided to each of the coils, as denoted by the schematic
electrical circuit associated with each supply (e.g., 281 and 285),
which is matched by the Focus Power Supply 275a. In this
embodiment, the current supplied in the coil is substantially
constant, and results in a current flow within each coil as denoted
by the letter `I` and corresponding arrow, in turn resulting in a
magnetic field schematically denoted at 261a. The magnitude of the
current is selected so as to provide a desired magnetic field that
results in a desired focusing effect.
[0203] Also, the cathode quadrupole core 204 is further configured
to provide a steering effect in a manner that does not require
additional coils. To do so, one or both coils 208a and 208b are
provided with--in addition to the constant focus current described
above--an X AC offset current and a Y AC offset current. The
duration of the AC offset currents are at a predetermined frequency
and the respective offset current magnitudes are designed to
achieve a desired an offset or shifting of the center of the
quadrupole field and, in turn, a resultant shift in the electron
beam (and focal spot) from the center axis of the cores. Thus,
coils 208a and 208b are driven independently, with a constant focus
current, and steering perturbations are created in the magnetic
field at the desired focal spot steering frequency by application
of desired X AC offset and Y AC offset currents in at least one
coil of corresponding coil pairs (e.g., opposing coils) of the
cathode quadrupole core 204. This effectively moves the center of
the magnetic field in the `x` and/or `y` direction, which in turn
results in a shifting of the electron beam (and resultant position
of the focal spot on the anode target) in a prescribed `x` and/or
`y` direction.
[0204] As is further shown in FIG. 12B, the illustrated example
includes a Focus Power Supply 275b for providing a predetermined
constant current in two of the four coils (e.g., 210a and 210b),
which are connected in electrical series, as denoted schematically
at 252, 252a, and 252b. Additionally, two of the coils (e.g., 212a
and 212b) include separate and independent power sources for
providing current to induce a magnetic field in a respective coil,
each power supply being denoted at 282 (Power Supply B) and 286
(Power Supply D). For purposes of providing a quadrupole magnetic
field, a constant `Focus Current` is provided to each of the coils,
as denoted by the schematic electrical circuit associated with each
supply (e.g., 283 and 287), which is matched by the Focus Power
Supply 275b. In this embodiment, the current supplied results in
the current in the coil being substantially constant, and results
in a current flow within each coil as denoted by the letter `I` and
corresponding arrow, in turn resulting in a magnetic field
schematically denoted at 261b. The magnitude of the current is
selected so as to provide a desired magnetic field that results in
a desired focusing effect. The focus current in the anode
quadrupole core 202 is opposite to the cathode quadrupole core 204
focus current so as to provide for complimentary magnetic fields,
and required focusing effect.
[0205] Also, the anode quadrupole core 202 is further configured to
provide a steering effect in a manner that does not require
additional coils. To do so, one or both of the coils 212a and 212b
are provided with--in addition to the constant focus current
described above--an X AC offset current and a Y AC offset current.
The duration of the AC offset currents are at a predetermined
frequency and the respective AC offset current magnitudes are
designed to achieve a desired shifted quadrupole field (e.g.,
center of quadrupole shifted in X and/or Y) and, in turn, a
resultant shift in the electron beam (and focal spot). Thus, coils
212a and 212b are driven independently, with a constant focus
current, and steering perturbations are created in the magnetic
field at the desired focal spot steering frequency by application
of desired X AC offset and Y AC offset currents to one coil or both
coils of the steering coil pairs of the anode quadrupole core 202.
This effectively moves the center of the magnetic field in the `x`
and/or `y` direction, which in turn results in a shifting of the
electron beam (and resultant position of the focal spot on the
anode target) in a prescribed `x` and/or `y` direction. Thus, the
combination of coil pairs 208a,b and coil pairs 212a,b provide
steering in both the "x" and "y;" directions.
[0206] Reference is next made to FIG. 12C, which illustrates a
functional diagram illustrating an embodiment of a magnetic control
system for controlling the operation of the quadrupole system of
FIGS. 12A-12B. At a high level, the magnetic control system of FIG.
12C provides the requisite control of coil currents supplied to the
quadrupole cores 202 and 204 so as to (1) provide a requisite
quadrupole field so as to achieve a desired focus of the focal
spot; and (2) provide a requisite shifted quadrupole field so as to
achieve a desired position of the focal spot. As noted, control of
the coil currents is accomplished in a manner so as to achieve a
desired steering frequency.
[0207] The embodiment of FIG. 12C includes a command processing
device 276, which may be implemented with any appropriate
programmable device, such as a microprocessor or microcontroller,
or equivalent electronics. The command processing device 276
controls, for example, the operation of each of the independent
power supplies (i.e., which provide corresponding coils operating
current to create a magnetic field), preferably in accordance with
parameters stored in non-volatile memory, such as that denoted at
Command Inputs 290. For example, in an example operational scheme,
parameters stored/defined in Command Inputs 290 might include one
or more of the following parameters relevant to the focusing and
steering of the focal spot: Tube Current (a numeric value
identifying the operational magnitude of the tube current, in
milliamps); Focal Spot L/S (such as `large` or `small` focal spot
size); Start/Stop Sync (identifying when to power on and power off
focusing); Tube Voltage (specifying tube operating voltage, in
kilovolts); Focal Spot Steering Pattern (for example, a numeric
value indicating a predefined steering pattern for the focal spot;
and Data System Sync (to sync an X-ray beam pattern with a
corresponding imaging system).
[0208] In an exemplary implementation, Command Inputs 290 can
correspond to requisite values in a look-up table arrangement.
Focus Power Supply 275a and Focus Power Supply 275b supply constant
focus current to the coils of the cores 202 and 204 of FIGS.
12A-12B. Similarly, Power Supply A (280), Power Supply B (282),
Power Supply C (284) and Power Supply D (286) supply constant focus
current to the corresponding coils of the cores 202 and 204 for the
focusing component of each coil, and an AC offset current for
purposes of shifting the quadrupole from the central axis.
[0209] Thus, by way of one example, a Focal Spot size specified as
`small` can cause the Command Processing unit 276 to control the
Focus Power Supply 275a and Focus Power Supply 275b to provide a
constant focus current having the prescribed magnitude
(corresponding to a `small` focal spot) to each of the coils (206a,
210a, 206b, 210b) of the cores 202 and 204, as described above.
Similarly, each of the Power Supplies 280 (coil 208a), 282 (coil
212b), 284 (coil 208b), and 286 (coil 212a) can also be controlled
to provide a constant focus current, having the same magnitude as
supplied by Focus Power Supply 275a and Focus Power Supply 275b.
Again, this can result in a quadrupole magnetic field that imposes
focusing forces on the electron beam so as to result in a `small`
focal spot on the anode target.
[0210] Similarly, a FS Steering Pattern might prescribe a specific
focal spot steering frequency and requisite displacement in an `x`
and/or `y` direction. This can result in Command Processing unit
276 to control each of the Power Supplies 280, 282, 284, and 286 to
supply a requisite X AC offset and Y AC offset current magnitudes
to one coil, a pair of coils, three coils, or the pairs of coils of
the corresponding coils of the cores 202 and 204, thereby creating
a desired shifted quadrupole field for the steering effect, in
addition to the beam (focal spot) focus, as described above.
[0211] In one embodiment, the steering quadrupole core can be
operated under high speed switching. Such high speed switching can
be at 6.5 to 7 kHz, and may include 20 microsecond transition
times. Also, the focusing can have a magnetic flux that is about
400 gauss, whereas the steering can have a magnetic flux of 30-40.
However, these values may vary, such as by 1, 2, 5, 10, or 20%.
[0212] An X-ray tube comprising: a cathode including an emitter,
wherein the emitter has a substantially planar surface configured
to emit electrons in an electron beam in a non-homogenous manner;
an anode configured to receive the emitted electrons; a first
magnetic quadrupole formed on a first yoke and having a magnetic
quadrupole gradient for focusing the electron beam in a first
direction and defocusing the electron beam in a second direction
perpendicular to the first direction; a second magnetic quadrupole
formed on a second yoke and having a magnetic quadrupole gradient
for focusing the electron beam in the second direction and
defocusing the electron beam in the first direction; wherein a
combination of the first and second magnetic quadrupoles provides a
net focusing effect in both first and second directions of a focal
spot of the electron beam; and at least one coil of a pair of
quadrupole coils having AC offset configured to deflect the
electron beam in order to shift the focal spot of the electron beam
on a target, at least one coil of a pair of quadrupole coils having
AC offset being on the first yoke, the second yoke or on both the
first and the second yoke.
[0213] It will be appreciated that various implementations of the
electron beam steering, as described herein, can be used
advantageously in connection with the tunable emitter, and that
features of each are complementary to one another. However, it will
also be appreciated that various features--of either electron beam
steering or of the planar emitter--do not need to be used together,
and have applicability and functionality in separate
implementations.
[0214] In one embodiment, an X-ray tube can include: a cathode
including an electron emitter that emits an electron beam; an anode
configured to receive the emitted electrons of the electron beam; a
first magnetic quadrupole between the cathode and the anode and
having a first quadrupole yoke with four evenly distributed first
quadrupole pole projections extending from the first quadrupole
yoke and oriented toward a central axis of the first quadrupole
yoke and each of the four first quadrupole pole projections having
a first quadrupole electromagnetic coil operably coupled to a power
supply system that provides a constant current to each first
quadrupole electromagnetic coil to produce a first focusing
magnetic quadrupole field; a second magnetic quadrupole between the
first magnetic quadrupole and the anode and having a second
quadrupole yoke with four evenly distributed second quadrupole pole
projections extending from the second quadrupole yoke and oriented
toward a central axis of the second quadrupole yoke and each of the
four second quadrupole pole projections having a second quadrupole
electromagnetic coil operably coupled to the power supply system
that provides a constant current to each second quadrupole
electromagnetic coil to produce a second focusing quadrupole field;
and at least one coil of a pair of opposing quadrupole
electromagnetic coils of the first or second quadrupole
electromagnetic coils operably coupled to the power supply system
that provides an alternating current offset to at least one coil of
the pair of opposing quadrupole electromagnetic coils to shift the
first and/or second focusing quadrupole field from the central axis
of the first and/or second quadrupole yokes. In one aspect, the
X-ray tube can include two pairs of opposing quadrupole
electromagnetic coils of the first and/or second quadrupole
electromagnetic coils, which are operably coupled to the power
supply system that provides an alternating current offset to at
least one coil of each pair of the two pairs of opposing quadrupole
electromagnetic coils to shift the first and/or second focusing
quadrupole field from the central axis of the first and/or second
quadrupole yokes.
[0215] In one aspect, a first pair of coils having AC offset is in
a first plane and a second pair of coils having AC offset is in a
different second plane. In one aspect, the first quadrupole
electromagnetic coils form the two pairs of coils with AC offset.
In one aspect, the second quadrupole electromagnetic coils form the
two pairs of coils with AC offset. In one aspect, the second
quadrupole electromagnetic coils form the two pairs of coils with
at least one coil of each coil pair having AC offset. In one
aspect, the two pairs of coils with at least one coil of each pair
having AC offset are orthogonal.
[0216] In one embodiment, the X-ray tube has four power supplies.
Each of these power supplies is operably coupled with only one of
the first or second quadrupole electromagnetic coils so as to form
the two pairs of coils, each pair of coils having at least one coil
with AC offset.
[0217] In one embodiment, a first focus power supply is operably
coupled with at least two opposing first quadrupole electromagnetic
coils. Often, the first focus power supply is operably coupled with
four quadrupole electromagnetic coils. In one aspect, a second
focus power supply is operably coupled with at least two opposing
second quadrupole electromagnetic coils. When a power supply is
operably coupled with two quadrupole electromagnetic coils, the
other two electromagnetic coils of the particular quadrupole have
independent power supplies or opposing pairs of coils have
independent power supplies. If one quadrupole has all four
electromagnetic coils operably coupled with a common power supply,
then the other quadrupole has all four electromagnetic coils
operably coupled to four different power supplies. However, it
should be recognized that a single power supply can be coupled to
any number of coils to provide the same power to those coils, such
as 2, 3, or 4 coils. Also, it may be possible for a single power
supply to provide different currents to different coils.
[0218] In one embodiment, the X-ray tube can include: the first
magnetic quadrupole being configured for providing a first magnetic
quadrupole gradient for focusing the electron beam in a first
direction and defocusing the electron beam in a second direction
orthogonal to the first direction; the second magnetic quadrupole
being configured for providing a second magnetic quadrupole
gradient for focusing the electron beam in the second direction and
defocusing the electron beam in the first direction. In one aspect,
a combination of the first and second magnetic quadrupoles provides
a net focusing effect in both first and second directions of a
focal spot of the electron beam.
[0219] In one embodiment, the X-ray tube can include two pairs of
opposing coils with one coil of each coil pair having AC offset,
where the two pairs of coils are configured to deflect the electron
beam in two different directions in order to shift a focal spot of
the electron beam on a target surface of the anode. The two pairs
of opposing coils with AC offset are formed from two pairs of
opposing coils of the quadrupole coils.
[0220] In one embodiment, the X-ray tube includes: the four first
quadrupole pole projections having the first quadrupole
electromagnetic coils being at 45, 135, 225, and 315 degrees; and
the four second quadrupole pole projections having the second
quadrupole electromagnetic coils being at 45, 135, 225, and 315
degrees.
[0221] In one embodiment, the X-ray tube can include the electron
emitter having a substantially planar surface configured to emit
electrons in an electron beam in a non-homogenous manner. In one
aspect, the cathode can have a cathode head surface with one or
more focusing elements located adjacent to the electron emitter.
The emitter can be any electron emitter having a configuration to
emit electrons in the electron beam to be substantially laminar
beam. Any emitter that emits a substantially laminar beam (e.g.,
significantly laminar beam) can be used with the focusing and
steering systems described herein.
[0222] In one embodiment, the X-ray tube can include: the first
magnetic quadrupole being operably coupled with a first focus power
supply; and each quadrupole electromagnetic coil with AC offset
being operably coupled with a different steering power supply.
[0223] In one embodiment, an X-ray tube can include: a cathode
including an emitter; an anode configured to receive the emitted
electrons; a first magnetic quadrupole formed on a first yoke and
having a magnetic quadrupole gradient for focusing the electron
beam in a first direction and defocusing the electron beam in a
second direction perpendicular to the first direction; and a second
magnetic quadrupole formed on a second yoke and having a magnetic
quadrupole gradient for focusing the electron beam in the second
direction and defocusing the electron beam in the first direction.
In one aspect, a combination of the first and second magnetic
quadrupoles provides a net focusing effect in both first and second
directions of a focal spot of the electron beam. In one aspect,
electromagnet pairs of the first magnetic quadrupole or second
magnetic quadrupole have AC offset to produce a shifted quadrupole
field configured to deflect the electron beam in order to shift the
focal spot of the electron beam on a target of the anode. In one
aspect, the X-ray tube includes two electromagnet pairs of the
first magnetic quadrupole and/or second magnetic quadrupole having
AC offset to produce a shifted quadrupole field configured to
deflect the electron beam in two orthogonal directions in order to
shift the focal spot of the electron beam on a target of the anode.
In one aspect, both pairs of opposing coils having AC offset are
configured on the first yoke or the second yoke, or one pair of
opposing coils having AC offset on each of the first yoke and the
second yoke.
[0224] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing an X-ray tube
of one of the embodiments (e.g., having at least one pair of
opposing coils with one coil of each pair having AC offset);
operating the electron emitter so as to emit the electron beam from
the cathode to the anode along an electron beam axis; operating the
first magnetic quadrupole to focus the electron beam in a first
direction; operating the second magnetic quadrupole to focus the
electron beam in a second direction orthogonal with the first
direction; and operating the pair of opposing coils with AC offset
to steer the electron beam away from the electron beam axis. In one
aspect, the method can include operating opposing quadrupole
electromagnetic coils with AC offset to have different powers to
form an asymmetric quadrupole moment that is shifted from a central
axis. In one aspect, the method can include forming a plurality of
different focal spots at different locations on the anode for a
given time interval, which time interval can be about 0.1, 0.2,
0.25, 0.3, 0.4, 0.5, 0.75, 1, 2, 3, 4, or 5 seconds, and generally
less than 30 seconds. In one aspect, the method can include forming
a plurality of different focal spots having different focal spot
areas for a given time interval, which time interval can be the
same or different from above.
[0225] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing the X-ray
tube of one of the embodiments (e.g., having at least two pair of
opposing coils with one coil of each pair having AC offset);
operating the electron emitter so as to emit the electron beam from
the cathode to the anode along an electron beam axis; operating the
first magnetic quadrupole to focus the electron beam in a first
direction; operating the second magnetic quadrupole to focus the
electron beam in a second direction orthogonal with the first
direction; operating a first pair of opposing coils with at least
one coil of the first pair having AC offset to steer the electron
beam away from the electron beam axis in a first direction; and
operating a second pair of opposing coils with at least one coil of
the second pair AC offset to steer the electron beam away from the
electron beam axis in a second direction that is orthogonal to the
first direction. In one aspect, the method can include operating
opposing quadrupole electromagnetic coils independently with AC
offset to have different currents to form a first asymmetric
quadrupole moment. In one aspect, the method can include operating
opposing quadrupole electromagnetic coils independently with AC
offset to have different currents to form a second asymmetric
quadrupole moment.
[0226] In one embodiment, one or both of the quadrupole cores can
be devoid of electromagnetic coils wrapped around the core. The
coils are on the pole projections, and the core is devoid of having
coils wrapped around the core between the pole projections.
IV. Example Embodiments of a Magnetic System providing Electron
Beam Focusing and Two-Axis Beam Steering via Two Quadrupoles and
Two Steering Coils Collocated on Pole Protrusions with Quadrupole
Coils
[0227] As noted above, certain embodiments include an electron beam
manipulation component that allows for steering and/or focusing of
the electron beam so as to control the position and/or size and
shape of the focal spot on the anode target. In one embodiment,
this manipulation is provided by way of a magnetic system
implemented as two magnetic quadrupoles and at least one pair of
steering coils disposed in the electron beam path. For example, in
one embodiment, two quadrupoles are used to provide focusing of the
electron beam, and at least one pair of steering coils is used to
provide steering of the electron beam. In this approach, focusing
magnetic fields can be provided by both quadrupoles (e.g., the
anode side quadrupole and the cathode side quadrupole) and the
electron beam steering magnetic fields can be provided by one or
two pair of steering coils. Alternatively, magnetic fields for
steering can be done for one direction with one pair of steering
coils and for the other direction with the other pair of shifting
coils, where the pairs are orthogonal with each other. Also, only
one steering coil of a steering coil pair needs to receive AC
offset in order to implement the steering function. As such,
embodiments may only include one steering coil for each steering
coil that is shown, thereby one steering coil of each steering coil
pair can be omitted.
[0228] In one embodiment, the steering is accomplished by the two
pairs of steering coils which are created by steering coils wound
on one of the core's poles projections adjacent with quadrupole
coils, where the quadrupole coils (e.g., wound on the same pole
projections as the steering coils) maintain the constant focusing
coil current. Steering of the electron beam (and resulting shifting
of the focal spot) occurs through appropriate steering coil pair
energizing and can be done in one axis or a combination of
axes.
[0229] FIG. 13 shows the components of the X-ray tube 100 (see
FIGS. 1A-1C) that are arranged for electron emission, electron beam
steering and/or focusing, and X-ray emission. In FIG. 13, disposed
within the beam path is a magnetic system 300 configured to focus
and steer the electron beam before reaching the anode 114, as noted
above. A portion of the cathode assembly 110 has the cathode head
115 with the electron emitter 122 on an end of the cathode head 115
so as to be oriented or pointed toward the anode 114 (see FIG. 1C
for orientation). The cathode head 115 can include a head surface
119 that has an emitter region that is formed as a recess that is
configured to receive the electron emitter 122 (e.g., planar
electron emitter). The head surface 119 also includes electron beam
focusing elements 111 located on opposite sides of the electron
emitter 122. The magnetic system 300 of FIG. 13 can replace the
magnetic system 180 of FIGS. 1A-1C, and thereby is useful in the
X-ray tube 100.
[0230] In this embodiment, the magnetic system 300 is implemented
as two magnetic cores 302, 304 that have quadrupoles disposed in
the electron beam path 112 of the X-ray tube 100. The combination
of the two magnetic cores 302, 304 are configured to (a) focus in
both directions perpendicular to the beam path, and (b) to steer
the beam in both directions perpendicular to the beam path. The
"focusing" provides a desired focal spot shape and size, and the
"steering" effects the positioning of the focal spot on the anode
target surface 128.
[0231] FIG. 14A shows an embodiment of an anode core 302 (e.g.,
closer to anode) having an anode yoke 302a, and FIG. 14B shows an
embodiment of a cathode core 304 (e.g., closer to cathode) having a
cathode yoke 304a. Each yoke 302a, 304a includes four pole
projections arranged in an evenly distributed and opposing
relationship, cathode pole projections 314a,b (e.g., first cathode
pole projections) and 316a,b (e.g., second cathode pole
projections) on the cathode yoke 304a, and anode pole projections
322a,b (e.g., first anode pole projections) and 324a,b (e.g.,
second anode pole projections) on the anode yoke 302a. Each pole
projection includes corresponding quadrupole electromagnetic coils,
denoted as cathode quadrupole coils 306a,b (e.g., first cathode
coils) and 308a,b (e.g., second cathode coils) on the cathode yoke
304a and anode quadrupole coils 310a,b (e.g., first anode coils)
and 312a,b (e.g., second anode coils) on the anode yoke 302a.
Additionally, the pole projections 322a,b and 324a,b of the anode
yoke 302a includes dipole coils 311a,b and 313a,b. Current is
supplied to the quadrupole coils so as to provide the desired
magnetic focusing effect, and current is supplied to the dipole
coils so as to provide the desired steering effect, as described
herein.
[0232] In this context, in conjunction with the embodiments shown
in FIGS. 1A-1C, 13, and 14A-14B (with reference to the magnetic
system 300 in particular), reference is further made to FIGS. 15A
and 15B. FIG. 15A shows an embodiment of a cathode core 304 having
a cathode yoke 304a and is configured as a quadrupole (e.g.,
cathode-side magnetic quadrupole 304), and FIG. 15B illustrates an
embodiment of an anode core 302 having an anode yoke 302a, also
configured as a quadrupole (e.g., anode-side magnetic quadrupole
302). As previously described in connection to FIGS. 14A-14B, in
this example each core section includes a yoke having four pole
projections arranged in an evenly distributed and opposing
relationship, pole projections 314a,b and 316a,b on the cathode
yoke 304a, and pole projections 322a,b and 324a,b on the anode yoke
302a. Each pole projection includes corresponding quadrupole coils,
denoted at 306a,b and 308a,b on the cathode core 304 and 310a,b and
312a,b on the anode core 302. Additionally, the pole projections
322a,b and 324a,b on the anode yoke 302a include steering coils,
denoted at 311a,b and 313a,b. The quadrupole coils 310a,b and
312a,b are closer to an end of the pole projections 322a,b and
324a,b, and the steering coils 311a,b and 313a,b are closer to the
yoke 202a; however, the orientation can be switched. While
illustrated as having a substantially circular shape, it will be
appreciated that each of the core (or yoke) portions 302a, 304a can
also be configured with different shapes, such as a square
orientation, semi-circular, oval, or other. Also, the location of
the quadrupole coils and dipole coils on the anode core pole
projections can be switched.
[0233] The two magnetic cores 302, 304 act as lenses, and may be
arranged so that the corresponding quadrupole electromagnets
thereof are parallel with respect to each other, and perpendicular
to the optical axis defined by the electron beam 112. The cores
together deflect the accelerated electrons such that the electron
beam 112 is focused in a manner that provides a focal spot with a
desired shape and size. Each quadrupole lens creates a magnetic
field having a gradient, where the magnetic field intensity differs
within the magnetic field. The gradient is such that the magnetic
quadrupole field focuses the electron beam in a first direction and
defocuses in a second direction that is perpendicular to the first
direction. The two quadrupoles can be arranged such that their
respective magnetic field gradients are rotated about 90.degree.
with respect to each other. As the electron beam traverses the
quadrupoles, it is focused to an elongated spot having a length to
width ratio of a desired proportion. As such, the magnetic fields
of the two quadrupole lenses can have a symmetry with respect to
the optical axis or with respect to a plane through the optical
axis.
[0234] In an example embodiment, the cathode core 304 focuses in a
length direction, and defocuses in width direction of the focal
spot. The electron beam is then focused in width direction and
defocused in length direction by the following anode core 302. In
combination the two sequentially arranged magnetic quadrupoles
insure a net focusing effect in both directions of the focal spot.
However, the focusing and defocusing axes of the two different
cores can be switched between the anode core 302 and cathode core
304.
[0235] The anode core 302 in one option can be further configured
to provide a steering effect that enables a shifting of the focal
spot in a plane perpendicular to an optical axis correspondent to
electron beam 112 of the X-ray tube 100 by having steering coils
collocated on the pole projections along with the quadrupole
coils.
[0236] With continued reference to FIG. 15A, a top view of a
cathode core 304 is shown. A circular core or yoke portion, denoted
at 304a is provided, which includes four pole projections 314a,
314b, 316a, 316b that are directed toward the center of the
circular yoke 304a. In an example implementation, the yoke 304a and
the pole projections 314a, 314b, 316a, 316b are constructed of core
iron. Moreover each coil can be comprised of 22 gauge magnet wire
at 60 turns; obviously other configurations can be suitable
depending on the needs of a particular application.
[0237] As is further shown in FIG. 15A, the illustrated example
includes a Focus Power Supply 1 375 for providing a predetermined
current to the four quadrupole coils, which are connected in
electrical series, as denoted schematically at 350, 350a, 350b
350c, and 350d. In this embodiment, the current supplied is
substantially constant, and results in a current flow within each
coil as denoted by the letter `I` and corresponding arrow, in turn
resulting in a magnetic field schematically denoted at 360. The
magnitude of the current is selected so as to provide a desired
magnetic field that results in a desired focusing effect. See FIG.
11A, which shows example focusing of the focal spot.
[0238] Reference is next made to FIG. 15B, which illustrates an
example of a top view of an anode core 302 having a circular core
or yoke 302a, which includes four pole projections 322a, 322b,
324a, 324b also directed toward the center of the circular yoke
302a. On each of the pole projections is provided a quadrupole
coil, as shown at 310a, 310b, 312a and 312b. In addition, a
steering coil is collocated on each of the pole projections, as
denoted at 311a, 311b and 313a, 313b. The anode core 302 and four
pole projections 322a, 322b, 324a, 324b can be comprised of a low
loss ferrite material so as to better respond to steering
frequencies (described herein). The coils can utilize similar gauge
magnet wire and similar turn ratio, with variations depending on
the needs of a given application.
[0239] As shown in the example embodiment of FIG. 15B, each of the
quadrupole coils 310a, 310b, 312a and 312b is connected in
electrical series to a Focus Power Supply 2 377 for providing a
predetermined focus current, as denoted schematically at 351, 351a,
351b, 351c, 351d. For purposes of providing a quadrupole magnetic
field, a constant `Focus Current` is provided to each of the
quadrupole coils, as already described. Moreover, as denoted by
current flow directional arrows at `I`, in turn resulting in a
magnetic field schematically denoted at 361. The focus current in
the anode core 302 is opposite to the cathode core 304 focus
current so as to provide for complimentary magnetic fields, and
thereby the focusing effect.
[0240] As is further shown in the example embodiment of FIG. 15B,
and in contrast with the quadrupole coils, each of the steering
coils 311a,b and 313a,b of the anode quadrupole core 302 includes a
separate and independent power source for providing current to
induce a magnetic field in a respective dipole coil, each power
supply being denoted at 380 (Power Supply A), 382 (Power Supply B),
384 (Power Supply C) and 386 (Power Supply D). For purposes of
providing a shifted quadrupole field, an AC offset `Steering
Current` is provided to each of the steering coils, as denoted by
the schematic electrical circuit associated with each supply (e.g.,
381, 383, 385, 387). However, two or more coils may receive zero AC
offset.
[0241] The anode core 302 is further configured to provide a
shifted quadrupole effect with the additional steering coils. To do
so, each of the activated steering coils is provided with an X
offset AC current and a Y offset AC current, where some steering
coils can have zero AC offset. The duration of the offset AC
currents are at a predetermined frequency and the respective offset
current magnitudes are designed to achieve a desired shifted
quadrupole field and, in turn, a resultant shift in the electron
beam (and focal spot) from a central axis of the cores. Each
steering coil is driven independently so that the steering coil
pairs have an appropriate current at the desired focal spot
steering frequency by application of desired X offset and Y offset
alternating currents in corresponding steering coils or steering
coil pairs. Quadrupole field perturbations are created in the
magnetic field at the desired focal spot steering frequency by
application of desired X offset and Y offset alternating currents
in corresponding steering coils or steering coil pairs (e.g.,
opposing steering coils) of the anode core 302. This effectively
moves the center of the magnetic field in the `x` and/or `y`
direction (see, for example, FIGS. 12B and 12C, which show a
representative steering effect), which in turn results in a
shifting of the electron beam (and resultant position of the focal
spot on the anode target) in a prescribed `x` and/or `y`
direction.
[0242] Reference is next made to FIG. 15C, which illustrates a
functional diagram illustrating an embodiment of a magnetic control
system for controlling the operation of the magnetic system of
FIGS. 15A-15B. At a high level, the magnetic control system of FIG.
15C provides the requisite control of coil currents supplied to the
cores 302 and 304 so as to (1) provide a requisite quadrupole field
so as to achieve a desired focus of the focal spot; and (2) provide
a shift in the quadrupole field so as to achieve a desired position
of the focal spot. As noted, control of the steering coil currents
is accomplished in a manner so as to achieve a desired steering
frequency.
[0243] The embodiment of FIG. 15C includes a Command Processing
device 376, which may be implemented with any appropriate
programmable device, such as a microprocessor or microcontroller,
or equivalent electronics. The Command Processing device 376
controls, for example, the operation of each of the independent
power supplies (i.e., which provide corresponding coils operating
current to create a magnetic field), preferably in accordance with
parameters stored in non-volatile memory, such as that denoted at
Command Inputs 390. For example, in an example operational scheme,
parameters stored/defined in Command Inputs 390 might include one
or more of the following parameters relevant to the focusing and
steering of the focal spot: Tube Current (a numeric value
identifying the operational magnitude of the tube current, in
milliamps); Focal Spot L/S (such as `large` or `small` focal spot
size); Start/Stop Sync (identifying when to power on and power off
focusing); Tube Voltage (specifying tube operating voltage, in
kilovolts); Focal Spot Steering Pattern (for example, a numeric
value indicating a predefined steering pattern for the focal spot);
and Data System Sync (to sync an X-ray beam pattern with a
corresponding imaging system).
[0244] In an exemplary implementation, Command Inputs 390 can
correspond to requisite values in a look-up table arrangement.
Focus Power Supply 1 375 supplies AC focus current to the
quadrupole coils of the cathode core 304 described above. Focus
Power Supply 2 377 supplies DC focus current to the coils of the
anode core 302 described above. Similarly, Power Supply A (380),
Power Supply B (382), Power Supply C (384) and Power Supply D (386)
supply AC offset current to the corresponding steering coils for
purposes of a steering effect so as to achieve a required electron
beam shift (focal spot movement).
[0245] Thus, by way of one example, a Focal Spot size specified as
`small` can cause the Command Processing unit 376 to control the
Focus Power Supply 1 375 and Focus Power Supply 2 377 to provide a
constant focus current (DC) having the prescribed magnitude
(corresponding to a `small` focal spot) to each of the quadrupole
coils of the cathode core 304 and anode core 302. Again, this can
result in a quadrupole magnetic field that imposes focusing forces
on the electron beam so as to result in a `small` focal spot on the
anode target.
[0246] Similarly, a FS Steering Pattern might prescribe a specific
focal spot steering frequency and requisite displacement in an `x`
and/or `y` direction. This can result in Command Processing unit
376 to control each of the Power Supplies 380, 382, 384, and 386 to
supply a requisite X-offset and Y-offset AC current magnitudes and
amplitudes to the corresponding steering coils of the anode core
302, thereby creating a desired steering effect. Also, the X-offset
and Y-offset current can be time varying steering current.
[0247] In an example embodiment, each of the Power Supplies 375,
377, 380, 382, 384 and 386 are high-speed switching supplies, and
which receive electrical power from a main power supply denoted at
392. Magnetic Control Status 394 receives status information
pertaining to the operation of the power supplies and the coils,
and may be monitored by command processing unit 376 and/or an
external monitor control apparatus (not shown).
[0248] Thus, in the embodiment of FIGS. 15A-15C, a magnetic system
providing electron beam focusing and two-axis beam steering via two
quadrupoles and two pairs of collocated steering coils is provided.
While an example embodiment is shown, it will be appreciated that
alternate approaches are contemplated. For example, while steering
of the electron beam is provided by way of steering coils with the
two pair of steering coils formed on the anode core 302, it will be
appreciated that both the anode core 302 and the cathode core 304
might be constructed of a ferrite material, and the steering could
be "split" between the cores, each having a pair of steering coils
(e.g., the pairs are orthogonal) formed thereon to provide a
perturbed quadrupole field effect in one direction for example.
Other variations would also be contemplated. An operational
protocol can be similar to the protocol of FIG. 10 described
herein.
[0249] Accordingly, the offset can be applied to one coil or two
opposing coils. In one example, AC offset is only applied to one
coil to get steering in a diagonal direction. In another example,
AC offset can be applied to both coils of an opposing coil pair. In
one example, one coil of an opposing pair receives AC offset, and
the other coil of the opposing pair can be set at zero AC offset.
As such one coil can have AC offset in one coil set to zero and the
other opposing coil of the pair has an AC offset that is not zero.
In one embodiment, the coils of an opposing coil pair can have
different offsets. In one embodiment, the AC offset in a pair of
opposing coils can be created by having one coil with zero offset
while the other has some offset. Application of AC offset to only
one coil or having the coils of a coil pair with different AC
offset can be applied to all embodiments.
[0250] FIG. 16A shows an embodiment of a cathode core 304 having a
cathode yoke 304a and is configured as a quadrupole (e.g.,
cathode-side magnetic quadrupole) with a pair of steering coils,
and FIG. 16B illustrates an embodiment of an anode core 302 having
an anode yoke 302a, also configured as a quadrupole (e.g.,
anode-side magnetic quadrupole) with a pair of steering coils. The
subject matter of FIG. 16A can include aspects of FIG. 15A, and the
subject matter of FIG. 16B can include aspects of FIG. 15B as
described herein.
[0251] As is further shown in FIG. 16A, the illustrated example
includes a Focus Power Supply 1 375a for providing a predetermined
current to the quadrupole coils (e.g., 306a, 306b, 308a, 308b),
which are connected in electrical series, as denoted schematically
at 352, 352a, 352b, 352c, and 352d. The quadrupole coils are
operated with constant focus current as described herein. In this
embodiment, the current supplied is substantially constant, and
results in a current flow within each quadrupole coil as denoted by
the letter `I` and corresponding arrow, in turn resulting in a
magnetic field schematically denoted at 361a. The magnitude of the
current is selected so as to provide a desired magnetic field that
results in a desired focusing effect.
[0252] Also, the cathode core 304 is further configured to provide
a steering effect. Accordingly, two of the pole projections (e.g.,
316a and 316b) have steering coils 311a and 311b that each include
a separate and independent power source for providing current to
induce a magnetic field in a respective steering coil, each power
supply being denoted at 380 (Power Supply A) and 384 (Power Supply
C). To do so, the steering coils 311a and 311b are provided with an
X-offset current and a Y-offset AC current. The duration of the
offset AC currents are at a predetermined frequency and the
respective offset current magnitudes are designed to achieve a
desired perturbed quadrupole field and, in turn, a resultant shift
in the electron beam (and focal spot). Thus, steering coils 311a
and 311b are driven independently with perturbations that are
created in the magnetic field at the desired focal spot steering
frequency by application of desired X offset and Y offset currents
as steering pairs of the cathode core 304. This effectively moves
the center of the quadrupole magnetic field in the `x` and/or `y`
direction, which in turn results in a shifting of the electron beam
(and resultant position of the focal spot on the anode target) in a
prescribed `x` and/or `y` direction.
[0253] As is further shown in FIG. 16B, the illustrated example
includes a Focus Power Supply 377a for providing a predetermined
current to the four quadrupole coils (e.g., 310a, 310b, 312a,
312b), which are connected in electrical series, as denoted
schematically at 353, 353a, 353b, 353c, and 353d. The quadrupole
coils are operated with constant focus current as described herein.
In this embodiment, the current supplied is substantially constant,
and results in a current flow within each quadrupole coil as
denoted by the letter `I` and corresponding arrow, in turn
resulting in a magnetic field schematically denoted at 361b. The
magnitude of the current is selected so as to provide a desired
magnetic field that results in a desired focusing effect. The focus
current in the anode core 302 is opposite to the cathode core 304
focus current so as to provide for complimentary magnetic fields,
and required focusing effect.
[0254] Also, the anode core 302 is further configured to provide a
steering effect. Accordingly, two of the pole projections (e.g.,
324a and 324b) have steering coils 313a and 313b that each include
a separate and independent power source for providing current to
induce a magnetic field in a respective steering coil, each power
supply being denoted at 382 (Power Supply B) and 386 (Power Supply
D). To do so, the steering coils 313a and 313b are provided with an
X-offset current and a Y-offset AC current, where one steering coil
can have zero AC offset. The duration of the offset currents are at
a predetermined frequency and the respective offset current
magnitudes are designed to achieve a desired dipole field and, in
turn, a resultant shift in the electron beam (and focal spot).
Thus, steering coils 313a and 313b are driven independently with
steering perturbations that are created in the magnetic field at
the desired focal spot steering frequency by application of desired
X-offset and Y-offset currents as steering coil pairs of the anode
core 302. This effectively moves the center of the magnetic field
in the `x` and/or `y` direction, which in turn results in a
shifting of the electron beam (and resultant position of the focal
spot on the anode target) in a prescribed `x` and/or `y` direction.
Thus, the combination of steering coil pairs 311a,b and steering
coil pairs 313a,b provide steering in both the "x" and "y;"
directions.
[0255] The cores 302, 304 of FIGS. 16A and 16B can be operated the
same as described in connection with FIGS. 15A and 15B with FIG.
15C. However, with FIGS. 16A and 16B, the focus power supplies are
Focus Power Supply 1 375a and Focus Power Supply 2 377a.
Accordingly, having one pair of steering coils on the anode
quadrupole core 302 and having one pair of steering coils on the
cathode quadrupole core 304 can provide for both cores 302, 304
implementing focusing, and the cathode core 304 implementing
steering in a first direction and the anode core 302 implementing
steering in a second direction that is perpendicular with the first
direction.
[0256] In one embodiment, the steering quadrupole core can be
operated under high speed switching with the AC current. Such high
speed switching can be at 6.5 to 7 kHz, and may include 20
microsecond transition times. Also, the focusing can have a
magnetic flux that is about 400 gauss, whereas the steering can
have a magnetic flux of 30-40. However, these values may vary, such
as by 1, 2, 5, 10, or 20%.
[0257] In one embodiment, an X-ray tube can include: a cathode
including an emitter, wherein the emitter has a substantially
planar surface configured to emit electrons in an electron beam in
a non-homogenous manner; an anode configured to receive the emitted
electrons; a first magnetic quadrupole formed on a first yoke and
having a magnetic quadrupole gradient for focusing the electron
beam in a first direction and defocusing the electron beam in a
second direction perpendicular to the first direction; a second
magnetic quadrupole formed on a second yoke and having a magnetic
quadrupole gradient for focusing the electron beam in the second
direction and defocusing the electron beam in the first direction;
wherein a combination of the first and second magnetic quadrupoles
provides a net focusing effect in both first and second orthogonal
directions of a focal spot of the electron beam; and at least one
steering coil or a pair of steering coils configured to deflect the
electron beam in order to shift the focal spot of the electron beam
on a target, the one steering coil or pair of steering coils being
on the first yoke or the second yoke, or one coil or a pair of
steering coils on the first yoke and one coil or a pair of steering
coils on the second yoke.
[0258] It will be appreciated that various implementations of the
electron beam steering, as described herein, can be used
advantageously in connection with the tunable emitter, and that
features of each are complementary to one another. However, it will
also be appreciated that various features--of either electron beam
steering or of the planar emitter--do not need to be used together,
and have applicability and functionality in separate
implementations.
[0259] In one embodiment, an X-ray tube can include: a cathode
including an electron emitter that emits an electron beam (e.g.,
substantially laminar beam); an anode configured to receive the
electron beam; a first magnetic quadrupole between the cathode and
the anode and having a first yoke with four evenly distributed
first pole projections extending from the first yoke and oriented
toward a central axis of the first yoke and each of the four first
pole projections having a first quadrupole electromagnetic coil; a
second magnetic quadrupole between the first magnetic quadrupole
and the anode and having a second yoke with four evenly distributed
second pole projections extending from the second yoke and oriented
toward a central axis of the second yoke and each of the four
second pole projections having a second quadrupole electromagnetic
coil; and one steering coil on a pole projection or a pair of
opposing steering coils on a pair of opposing pole projections of
the first or second pole projections. In one aspect, the X-ray tube
can include two pairs of steering coils formed from two pairs of
opposing steering coils on the first and/or second pole
projections. In one aspect, the two pair of steering coils are both
in a plane formed by one of the first yoke or second yoke. In one
aspect, a first pair of steering coils of the two pair of steering
coils is in a first plane (e.g., cathode core) and a second pair of
steering coils is in a different second plane (e.g., anode core).
In one aspect, the first pole projections each have the steering
coils so as to form the two pair of steering coils. In one aspect,
the second pole projections each have the steering coils so as to
form the two pair of steering coils. In one aspect, the two pair of
steering coils are orthogonal. In one aspect, one coil of each coil
pair can be omitted or have zero AC offset.
[0260] In one embodiment, the X-ray tube can include four power
supplies, each being operably coupled with a steering coil. In one
aspect, the X-ray tube can include a first focus power supply
operably coupled with the first quadrupole electromagnetic coils;
and/or a second focus power supply operably coupled with the second
quadrupole electromagnetic coils.
[0261] In one embodiment, the X-ray tube can include: the first
magnetic quadrupole being configured for providing a first magnetic
quadrupole gradient for focusing the electron beam in a first
direction and defocusing the electron beam in a second direction
orthogonal to the first direction; the second magnetic quadrupole
being configured for providing a second magnetic quadrupole
gradient for focusing the electron beam in the second direction and
defocusing the electron beam in the first direction; and wherein a
combination of the first and second magnetic quadrupoles provides a
net focusing effect in both first and second directions of a focal
spot of the electron beam. In one aspect, the X-ray tube can
include one steering coil, a pair of steering coils, three coils,
or two pairs of steering coils being configured to deflect the
electron beam in order to shift a focal spot of the electron beam
on a target surface of the anode.
[0262] In one aspect, the four first pole projections can be at 45,
135, 225, and 315 degrees, and the four second pole projections can
be at 45, 135, 225, and 315 degrees.
[0263] In one embodiment, the X-ray tube can include the electron
emitter, such as any emitter that can emit a substantially laminar
beam. For example, the emitter can have a substantially planar
surface configured to emit electrons in an electron beam in a
non-homogenous manner. In one aspect, the cathode can have a
cathode head surface with one or more focusing elements located
adjacent to the electron emitter. The emitter can be any electron
emitter having a configuration to emit electrons in the electron
beam to be substantially laminar. Any emitter that emits a
substantially laminar beam (e.g., significantly laminar beam) can
be used with the focusing and steering systems described
herein.
[0264] In one embodiment, the X-ray tube can include the four
second pole projections having the four second quadrupole
electromagnetic coils adjacent to pole projection ends. Also, the
X-ray tube can include the four second pole projections having four
steering coils between the four second quadrupole electromagnetic
coils and the second yoke.
[0265] In one embodiment, an X-ray tube can include: a cathode
including an emitter; an anode configured to receive the emitted
electrons; a first magnetic quadrupole formed on a first yoke and
having a magnetic quadrupole gradient for focusing the electron
beam in a first direction and defocusing the electron beam in a
second direction perpendicular to the first direction; a second
magnetic quadrupole formed on a second yoke and having a magnetic
quadrupole gradient for focusing the electron beam in the second
direction and defocusing the electron beam in the first direction;
wherein a combination of the first and second magnetic quadrupoles
provides a net focusing effect in both first and second directions
of a focal spot of the electron beam; and at least one of the first
yoke or second yoke has two opposing pole projections each with a
steering coil that together perturb the quadrupole field so as to
deflect the electron beam in order to shift the focal spot of the
electron beam on a target of the anode.
[0266] In one embodiment, at least one of the first yoke or second
yoke has two pairs of opposing pole projections, each pole
projection with a steering coil. In one aspect, each pair of two
opposing steering coils deflect the electron beam in order to shift
the focal spot of the electron beam on a target of the anode. In
one aspect, both pair of steering coils are configured on the first
yoke or the second yoke, or one pair of steering coils one each of
the first yoke and the second yoke.
[0267] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing an X-ray tube
of one of the embodiments (e.g., having at least one pair of
steering coils); operating the electron emitter so as to emit the
electron beam from the cathode to the anode along an electron beam
axis; operating the first magnetic quadrupole to focus the electron
beam in a first direction; operating the second magnetic quadrupole
to focus the electron beam in a second direction orthogonal with
the first direction; and operating the pair of steering coils so as
to steer the electron beam away from the electron beam axis. In one
aspect, the method can include operating opposing steering coils of
the pair to have different powers to form an asymmetric quadrupole
field. In one aspect, the method can include forming a plurality of
different focal spots at different locations on the anode for a
given time interval, which time interval can be about 0.1, 0.2,
0.25, 0.3, 0.4, 0.5, 0.75, 1, 2, 3, 4, or 5 seconds, and generally
less than 30 seconds. In one aspect, the method can include forming
a plurality of different focal spots having different focal spot
areas for a given time interval, which time interval can be the
same or different from above.
[0268] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing the X-ray
tube of one of the embodiments (e.g., having at least two pairs of
steering coils); operating the electron emitter so as to emit the
electron beam from the cathode to the anode along an electron beam
axis; operating the first magnetic quadrupole to focus the electron
beam in a first direction; operating the second magnetic quadrupole
to focus the electron beam in a second direction orthogonal with
the first direction; operating a first pair of steering coils to
steer the electron beam away from the electron beam axis in a first
direction; and operating a second pair of steering coils to steer
the electron beam away from the electron beam axis in a second
direction that is orthogonal to the first direction. In one aspect,
the method can include operating opposing steering coils of the
first pair of steering coils to have different powers to form a
first asymmetric quadrupole field. In one aspect, the method can
include operating opposing steering coils of the second pair of
steering coils to have different powers to form a second asymmetric
quadrupole field.
[0269] In one embodiment, one or both of the quadrupole cores can
be devoid of electromagnetic coils wrapped around the core. The
coils are on the pole projections, and the core is devoid of having
coils wrapped around the core between the pole projections.
V. Example Embodiments of a Magnetic System Providing Electron Beam
Focusing Via Two Quadrupole Cores and Two-Axis Beam Steering via
Two Dipoles on a Dipole Core
[0270] As noted above, certain embodiments include an electron beam
manipulation system that allows for steering and/or focusing of the
electron beam so as to control the position and/or size and shape
of the focal spot on the anode target. In one embodiment, this
manipulation is provided by way of a magnetic system implemented as
two magnetic quadrupole cores and one magnetic dipole core disposed
in the electron beam path. For example, in one embodiment, two
quadrupole cores are used to provide focusing of the electron beam
and the dipole core can also be used for steering. In this
approach, focusing magnetic fields would be provided by both
quadrupole cores (the anode side quadrupole core and the cathode
side quadrupole core) and the electron beam steering magnetic
fields would be provided by one of the quadrupole cores (e.g., the
anode side quadrupole core) or only by the dipole core.
Alternatively, magnetic fields for steering could be done for one
direction with one quadrupole and for the other direction with the
other quadrupole, or using the dipole for assistance in steering or
for performing all steering. In this way, combined beam focusing
can be provided using only quadrupoles. In another alternative, the
dipole can be used only for steering. Here, the dipole core can be
considered to be a steering core and the dipole coils can be
steering coils that are operated the same or similarly as the
steering coils described herein. Thus, reference of the dipole
coils can be indications of steering coils.
[0271] FIGS. 17A-17C are views of one example of an X-ray tube 100a
in which one or more embodiments described herein may be
implemented, and which include features of the X-ray tube 100,
except for the magnetic system 180 of FIGS. 1A-1C is substituted
with the magnetic system 400 of FIGS. 17A-17C. Specifically, FIG.
17A depicts a perspective view of the X-ray tube 100a and FIG. 17B
depicts a side view of the X-ray tube 100a, while FIG. 17C depicts
a cross-sectional view of the X-ray tube 100a. The X-ray tube 100a
illustrated in FIGS. 17A-17C represents an example operating
environment and is not meant to limit the embodiments described
herein. As shown, the magnetic system 400 includes a cathode
quadrupole core 404, an anode quadrupole core 402, and a dipole
core 450.
[0272] FIG. 17D shows the components of the X-ray device that are
arranged for electron emission, electron beam steering or focusing,
and X-ray emission. The cathode head 115 is shown with the planar
electron emitter 122 oriented so as to emit electrons in a beam 112
towards the anode 114. In FIG. 17D, disposed within the beam path
is the magnetic system 400 configured to focus and steer the
electron beam before reaching the anode 114, as noted above. The
magnetic system 400 includes a cathode quadrupole core 404, an
anode quadrupole core 402, and a dipole core 450. A portion of the
cathode assembly 110 has the cathode head 115 with the electron
emitter 122 on an end of the cathode head 115 so as to be oriented
or pointed toward the anode 114 (see FIG. 17C for orientation. The
cathode head 115 also includes electron beam focusing elements 311
located on opposite sides of the electron emitter 122.
[0273] Optionally, one or more electron beam manipulation
components can be provided. Such devices can be implemented so as
to "focus," "steer" and/or "deflect" the electron beam 112 as it
traverses the drift region 124, thereby manipulating or "toggling"
the position and/or dimension of the focal spot on the anode target
surface 128. Additionally or alternatively, a manipulation
component can be used to alter or "focus" the cross-sectional shape
(e.g., length and width) of the electron beam and thereby change
the shape and dimension of the focal spot on the anode target
surface 128.
[0274] One example of the magnetic system 400 and components
thereof is shown in FIGS. 18A-18C. In this embodiment, the magnetic
system 400 is implemented as two magnetic quadrupole cores 402, 404
and one magnetic dipole core 450 disposed in the electron beam path
112 of the X-ray tube 100a. The two quadrupole cores 402, 404 are
configured to (a) focus in both directions perpendicular to the
beam path, and optionally (b) to steer the beam in both directions
perpendicular to the beam path. In this way, the two quadrupole
cores 402, 404 act together to form a magnetic lens (sometimes
referred to as a "doublet"), and the focusing is accomplished as
the electron beam passes through the quadrupole "lens." The
steering is accomplished by the dipole. The "focusing" provides a
desired focal spot shape and size, and the "steering" effects the
positioning of the focal spot on the anode target surface 128. Each
quadrupole core 402, 404 is implemented with a core section, or a
yoke, denoted as a cathode quadrupole yoke at 404a, and an anode
quadrupole yoke at 402a. FIG. 18A shows an embodiment of an anode
quadrupole core 402 having an anode quadrupole yoke 402a, and FIG.
18B shows an embodiment of a cathode quadrupole core 404 having a
cathode quadrupole yoke 404a. Each quadrupole yoke 402a, 404a
includes four pole projections arranged in an opposing
relationship, cathode projections 414a,b (e.g., first cathode
projections) and 416a,b (e.g., second cathode projections) on the
cathode yoke 404a, and anode projections 422a,b (e.g., first anode
projections) and 424a,b (e.g., second anode projections) on the
anode yoke 402a. Each quadrupole pole projection includes
corresponding coils, denoted at cathode coils 406a,b (e.g., first
cathode coils) and 408a,b (e.g., second cathode coils) on the
cathode yoke 404a and anode coils 410a,b (e.g., first anode coils)
and 412a,b (e.g., second anode coils) on the anode yoke 402a.
Current is supplied to the coils so as to provide the desired
focusing and/or steering effect, as will be described in further
detail below.
[0275] The dipole core 450 as shown in FIG. 18C is implemented with
a core section or yoke, denoted at dipole yoke 450a. The dipole
yoke 450a includes four pole projections arranged in opposing
relationships, dipole projections 454a,b (e.g., first dipole
projections) and 456a,b (e.g., second dipole projections). Each
dipole projection includes corresponding coils, denoted at dipole
coils 458a,b (e.g., first dipole coils) and 460a,b (e.g., second
dipole coils). Current is supplied to the dipole coils so as to
provide the desired steering effect, as will be described in
further detail below.
[0276] The dipole core 450 as shown in FIG. 18D is implemented with
a core section or yoke, denoted at dipole yoke 450a. The dipole
yoke 450a includes four pole projections arranged in opposing
relationships, pole projections 454a,b (e.g., first dipole
projections) and 456a, b (e.g., second dipole projections). Between
the dipole projections are corresponding dipole coils, denoted at
dipole coils 458a,b (e.g., first dipole coils) and 460a,b (e.g.,
second dipole coils). Current is supplied to the coils so as to
provide the desired steering effect, as will be described in
further detail below. Here, the dipole coils are not on the
protrusions, but between the protrusions. In the embodiments that
utilize three cores, one being a dedicated dipole core, the
embodiment of FIG. 18D can be utilized with the power and
operability described herein, such as in connection to FIGS.
20A-20B and 21A-21B.
[0277] FIG. 19A shows an embodiment of a cathode core 404 having a
cathode yoke 404a configured as a quadrupole (e.g., cathode-side
magnetic quadrupole 404), and FIG. 19B illustrates an embodiment of
an anode core 402 having an anode yoke 402a, also configured as a
quadrupole (e.g., anode-side magnetic quadrupole 402). As
previously described, in this example each core section includes a
yoke having four pole projections arranged in an opposing
relationship, 414a,b and 416a,b on the cathode yoke 404a, and
422a,b and 424a,b on the anode yoke 402a. Each pole projection
includes corresponding coils, denoted at 406a,b and 408a,b on the
cathode core 404 and 412a,b and 410a,b on the anode core 402. While
illustrated as having a substantially circular shape, it will be
appreciated that each of the core (or yoke) portions 402a, 404a can
also be configured with different shapes, such as a square
orientation, semi-circular, oval, or other.
[0278] The two magnetic quadrupole cores 402, 404 act as lenses,
and may be arranged so that the corresponding electromagnets
thereof are in parallel with respect to each other, and
perpendicular to the optical axis defined by the electron beam 112.
The quadrupole cores together deflect the accelerated electrons
such that the electron beam 112 is focused in a manner that
provides a focal spot with a desired shape and size. Each
quadrupole lens creates a magnetic field having a gradient, where
the magnetic field intensity differs within the magnetic field. The
gradient is such that the magnetic quadrupole field focuses the
electron beam in a first direction and defocuses in a second
direction that is perpendicular to the first direction. The two
quadrupoles can be arranged such that their respective magnetic
field gradients are rotated about 90.degree. with respect to each
other. As the electron beam traverses the quadrupoles, it is
focused to an elongated spot having a length to width ratio of a
desired proportion. As such, the magnetic fields of the two
quadrupole lenses can have a symmetry with respect to the optical
axis or with respect to a plane through the optical axis.
[0279] With continued reference to the figures, the double magnetic
quadrupole includes an anode-side magnetic quadrupole core,
generally designated at 402 and a second cathode-side magnetic
quadrupole core, generally designated at 404, that are together
positioned approximately between the cathode and the target anode
and disposed around the neck portion 124a as previously described.
The anode side quadrupole core 402 in one option can be further
configured to provide a dipole field effect that enables a shifting
of the focal spot in a plane perpendicular to an optical axis
correspondent to electron beam 112 of the X-ray tube 100. In an
example embodiment, the cathode-side magnetic quadrupole core 404
focuses in a length direction, and defocuses in width direction of
the focal spot. The electron beam is then focused in a width
direction and defocused in length direction by the following
anode-side magnetic quadrupole core 402. In combination the two
sequentially arranged magnetic quadrupoles insure a net focusing
effect in both directions of the focal spot.
[0280] With continued reference to FIG. 19A, a top view of a
cathode-side magnetic quadrupole core 404 is shown. A circular core
or yoke portion, denoted at 404a is provided, which includes four
pole projections 414a, 414b, 416a, 416b that are directed toward
the center of the circular yoke 404a. On each of the pole
projections is provided a coil, as shown at 406a, 406b, 408a and
408b. In an example implementation, the yoke 404a and the pole
projections 414a, 414b, 416a, 416b are constructed of core iron.
Moreover each coil is comprised of 22 gauge magnet wire at 60
turns; obviously other configurations would be suitable depending
on the needs of a particular application.
[0281] As is further shown in FIG. 19A, the illustrated example
includes a Focus Power Supply 1 475 for providing a predetermined
constant current to the four coils, which are connected in
electrical series, as denoted schematically at 430, 430a, 430b
430c, and 430d. In this embodiment, the constant current supplied
is substantially constant, and results in a current flow within
each coil as denoted by the letter `I` and corresponding arrow, in
turn resulting in a magnetic field schematically denoted at 460.
The magnitude of the current is selected so as to provide a desired
magnetic field that results in a desired focusing effect.
[0282] Reference is next made to FIG. 19B, which illustrates an
example of a top view of an anode-side magnetic quadrupole core
402. As with quadrupole core 404, a circular core or yoke portion,
denoted at 402a is provided, which includes four pole projections
422a, 422b, 424a, 424b also directed toward the center of the
circular yoke 402a. On each of the pole projections is provided a
coil, as shown at 410a, 410b, 412a and 412b. In conjunction with
quadrupole core 404, the yoke 402a and projections on quadrupole
core 402 is comprised of the same material as for the cathode
quadrupole core 404, which can be core iron. However, the anode
quadrupole core 402 can be prepared from a low loss ferrite
material so as to better respond to steering frequencies (described
below). The coils can utilize similar gauge magnet wire and similar
turn ratio, with variations depending on the needs of a given
application.
[0283] As is further shown in FIG. 19B, the illustrated example
includes a Focus Power Supply 2 476 for providing a predetermined
constant current to the four coils, which are connected in
electrical series, as denoted schematically at 431, 431a, 431b,
431c, and 431d. In this embodiment, the constant current supplied
is substantially constant, and results in a constant current flow
within each coil as denoted by the letter `I` and corresponding
arrow, in turn resulting in a magnetic field schematically denoted
at 461. The magnitude of the current is selected so as to provide a
desired magnetic field that results in a desired focusing
effect.
[0284] FIG. 20A shows an embodiment of a dipole core 450 having a
dipole yoke 450a. Dipole coils 458a,b (e.g., first dipole coils)
and 460a,b (e.g., second dipole coils) are located on each of the
pole projections 454a,b (e.g., first dipole projections) and 456a,b
(e.g., second dipole projections). The first dipole coils 458a,b
are shown to be energized with AC offset by a first dipole power
supply (Steering Power Supply "A"), denoted at 575, and the second
dipole coils 460a,b are shown to be energized with AC offset by the
second dipole power supply (Steering Power Supply "B"), denoted at
585. The first dipole coils 458a,b cooperate to form the first
dipole magnetic field 560, and the second dipole coils 460a,b
cooperate to form the second dipole magnetic field 561. The dipole
core coils can be controlled independently, thereby the dipole pole
protrusions are offset or staggered compared to the quadrupole pole
protrusions that are at 45, 135, 225 and 315 degrees, in one
example, and thereby the dipole pole protrusions can be at 0, 90,
180, and 270 degrees. Accordingly, one coil of a coil pair can have
zero AC offset.
[0285] Another example of the dipole core 450 is shown in FIG. 20B,
where each of the dipole coils 458a, 458b, 460a and 460b is
connected to a separate and independent power source for providing
AC current to induce a magnetic field in the respective coil. The
power supplies are denoted at 580 (Steering Power Supply A), 582
(Steering Power Supply B), 584 (Steering Power Supply C) and 586
(Steering Power Supply D) and are electrically connected as denoted
by the schematic electrical circuit associated with each supply
(e.g., 581, 583, 585, 587). The dipole core coils can be controlled
independently, thereby the dipole pole protrusions are in line with
the quadrupole pole protrusions at 45, 135, 225 and 315 degrees, in
one example.
[0286] The configurations of FIGS. 20A and 20B provide for dipole
steering. The dipole pairs (e.g., 458a,b are a first dipole pair
and 460a,b are a second dipole pair) are configured to provide a
dipole magnetic effect, and the requisite dipole effect is provided
by supplying each of the dipole coils with an X-offset AC current
and a Y-offset AC current. The duration of the offset AC currents
are at a predetermined frequency and the respective offset current
magnitudes are designed to achieve a desired dipole field and, in
turn, a resultant shift in the electron beam (and focal spot).
Thus, each coil is driven independently (FIG. 20B) or each dipole
coil pair is driven independently (FIG. 20A) with an appropriate
current at the desired focal spot steering frequency by application
of desired X-offset and Y-offset AC currents in corresponding
dipole coils. This effectively moves the center of the magnetic
field in the `x` and/or `y` direction. The dipoles provide a
lateral force on the electrons as they pass through the region
between the pole faces. This force modulates the beam and during
the drift time, the electrons travel their modulated path and end
up at a desired focal spot. Due to the minimal mass of an electron,
they follow the changes in this magnetic field practically
instantaneously. Hence, operation of the X-ray tube can achieve
fast switching as the magnetic field acts on successive electrons
in the stream.
[0287] Reference is next made to FIGS. 21A-21B, which illustrate
functional diagrams illustrating an embodiment of a magnetic
control system for controlling the operation of the quadrupole
systems of FIGS. 19A-19B and dipoles of FIGS. 20A-20B. At a high
level, the magnetic control systems of FIGS. 21A-21B provide the
requisite control of coil currents supplied to the quadrupole core
pair 402 and 404 and/or dipole core 450 so as to (1) provide a
requisite quadrupole field so as to achieve a desired focus of the
focal spot; and (2) provide a requisite dipole field so as to
achieve a desired position of the focal spot. As noted, control of
the dipole coil AC currents is accomplished in a manner so as to
achieve a desired steering frequency.
[0288] The embodiment of FIG. 21A includes a Command Processing
device 676, which may be implemented with any appropriate
programmable device, such as a microprocessor or microcontroller,
or equivalent electronics. The Command Processing device 676
controls, for example, the operation of each of the independent
power supplies of FIGS. 19A-19B and 20A (i.e., which provide
corresponding coils operating current to create a magnetic field),
preferably in accordance with parameters stored in non-volatile
memory, such as that denoted at Command Inputs 690. For example, in
an example operational scheme, parameters stored/defined in Command
Inputs 690 might include one or more of the following parameters
relevant to the focusing and/or steering of the focal spot: Tube
Current (a numeric value identifying the operational magnitude of
the tube current, in milliamps); Focal Spot L/S (such as `large` or
`small` focal spot size); Start/Stop Sync (identifying when to
power on and power off focusing); Tube Voltage (specifying tube
operating voltage, in kilovolts); Focal Spot Steering Pattern (for
example, a numeric value indicating a predefined steering pattern
for the focal spot; and Data System Sync (to sync an X-ray beam
pattern with a corresponding imaging system).
[0289] In an exemplary implementation for the quadrupoles of FIGS.
19A and 19B and dipole of FIG. 20A as shown in FIG. 21A, the
Command Inputs 690 can be provided to Command Processing 676, which
then communicates with the Focus Power Supply 1 (475) and Focus
Power Supply 2 (476) for the quadrupoles and Steering Power Supply
A 575 and Steering Power Supply B 585 for the dipoles, which then
provide drive outputs for the cathode core focus coils and anode
core focus coils as well as the dipole steering coils.
[0290] Thus, by way of one example, a Focal Spot size specified as
`small` would cause the Command Processing unit 676 to control the
Focus Power Supply 1 475 to provide a constant focus current having
the prescribed magnitude (corresponding to a `small` focal spot) to
each of the coils (406b, 408a, 406a, 408b) of the cathode-side
magnetic quadrupole 404, as described above. Similarly, the Focus
Power Supply 2 476 would also be controlled to provide a constant
focus current, having the same magnitude as supplied by Focus Power
Supply 1 475, to each of the coils of the anode-side magnetic
quadrupole 402. Again, this would result in a quadrupole magnetic
field that imposes focusing forces on the electron beam so as to
result in a `small` focal spot on the anode target.
[0291] Also, a FS Steering Pattern might prescribe a specific focal
spot steering frequency and requisite displacement in an `x` and/or
`y` direction. This would result in Command Processing unit 676 to
control each of the Steering Power Supply A 575 and Steering Power
Supply B 585 to supply a requisite X-offset and Y-offset AC current
magnitudes to the corresponding coils of the dipole 450, thereby
creating a desired dipole steering effect, in addition to the beam
(focal spot) focus, as described above.
[0292] In an example embodiment, each of the Power Supplies 475,
476, 575, and 585 are high-speed switching supplies, and which
receive electrical power from a main power supply denoted at 692.
Magnetic Control Status 694 receives status information pertaining
to the operation of the power supplies and the coils, and may be
monitored by Command Processing unit 676 and/or an external monitor
control apparatus (not shown).
[0293] In yet another example embodiment, a magnetic system
implemented as two magnetic quadrupoles and a dipole can be
disposed in the electron beam path of an X-ray tube is provided.
Similar to the embodiment described above, the two magnetic
quadrupoles are configured to focus the electron beam path in both
directions perpendicular to the beam path. However, instead of
implementing a dipole function via a quadrupole as described above,
two dipoles are collocated on a dipole core to steer the beam in
both directions (`x` and `y`) perpendicular to the beam path. The
steering is accomplished by the two dipoles of the dipole core 450
which are created by dipole coils wound on one of the dipole core
450 pole projections 454a,b and 456a,b, while the quadrupole coils
maintain the focusing coil current. Steering of the electron beam
(and resulting shifting of the focal spot) occurs through
appropriate dipole coil pair energizing and can be done in one axis
or a combination of axes. In one embodiment, one quadrupole is used
to focus in the first direction and the second quadrupole to focus
in the second direction and the dipole core with two separate
dipoles to steer in both directions.
[0294] Reference is next made to FIGS. 19A-19B and 20B, which
together illustrate one example. Here, the dipole coils are
configured to provide a dipole magnetic effect, and the requisite
dipole effect is provided by supplying each of the dipole coils
with an X-offset AC current and a Y-offset AC current, where one or
more dipole coils can have zero AC offset. The duration of the
offset AC currents are at a predetermined frequency and the
respective offset current magnitudes are designed to achieve a
desired dipole field and, in turn, a resultant shift in the
electron beam (and focal spot). Thus, each coil is driven
independently, the quadrupole coils with a constant focus current,
and dipole coil pairs with an appropriate AC current at the desired
focal spot steering frequency by application of desired X-offset
and Y-offset currents in corresponding dipole coils. This
effectively moves the center of the magnetic field in the `x`
and/or `y` direction, which in turn results in a shifting of the
electron beam (and resultant position of the focal spot on the
anode target) in a prescribed `x` and/or `y` direction.
[0295] Reference is next made to FIG. 21B, which illustrates a
functional diagram illustrating an embodiment of a magnetic control
system for controlling the operation of the quadrupole and dipole
systems of FIGS. 19A-19B and 20B. At a high level, the magnetic
control system of FIG. 21B provides the requisite control of coil
currents supplied to the quadrupole coils and the dipole coils so
as to (1) provide a requisite quadrupole field so as to achieve a
desired focus of the focal spot; and (2) provide a requisite dipole
field so as to achieve a desired position of the focal spot. As
noted, control of the individual coil currents is accomplished in a
manner so as to achieve a desired steering frequency.
[0296] The functional processing associated with the magnetic
control system of FIG. 21B is similar in most respects to that of
FIG. 21A except that each of the Focus Power Supplies 1 (475) and 2
(476) provide a requisite focus DC current to the quadrupole coils,
and the Steering Power Supplies A (580), B (582), C (584) and D
(586) provide a requisite steering AC current and amplitude to the
dipole coils to provide a desired dipole magnetic effect so as to
achieve a required electron beam shift (focal spot movement).
[0297] Thus, in the embodiment of FIGS. 19A-19B, 20B, and 21B, a
magnetic system providing electron beam focusing and two-axis beam
steering via two quadrupoles and two dipoles (both on the same
dipole core) is provided. While an example embodiment is shown, it
will be appreciated that alternate approaches are contemplated. For
example, while steering of the electron beam is provided by way of
a dipole effect provided completely by the two dipoles, it will be
appreciated that both the anode core 402 and the cathode core 404
can facilitate focusing. Other variations would also be
contemplated.
[0298] In one aspect, the magnetic controller can be operated by
command inputs. For example, the following inputs (e.g., input by
user into controller) can be used to run the magnetic control
system: Implemented for focusing: Tube Current (mA), Numeric Input:
ex 450; Focal Spot (L/S), Large or Small Focal Spot; Start Stop
Sync, to determine when to power on focus and power off;
Implemented for focusing and steering: Tube Voltage (kV), Numeric
Input: ex 120; Implemented for Steering: FS Steering Pattern,
Pattern 1, 2, or 3, etc.; and Implemented for data collection: Data
System Sync, to sync beam pattern with imaging system.
[0299] In one aspect, the magnetic controller can be operated with
command inputs for focal spot control. For example, the following
inputs (e.g., input by user into controller) can be used to control
the focal spot. The user can implement command processing. This can
include the use of command inputs and lookup/calibration table to
determine: Focus Power Supply 1 current, which can be for cathode
core focus coils; Focus Power Supply 2 current, which can be for
anode core focus coils; Steering Power Supply A current and wave
form, which can be for Y-direction beam movement; Steering Power
Supply B current and wave form, which can be X-direction beam
movement; and Magnetic Control Status. If sources do not energize
then feedback can stop system from operating.
[0300] It will be appreciated that various implementations of the
electron beam focusing and steering, as described herein, can be
used advantageously in connection with the tunable emitter, and
that features of each are complementary to one another. However, it
will also be appreciated that various features--of either electron
beam steering or of the planar emitter--do not need to be used
together, and have applicability and functionality in separate
implementations.
[0301] In one embodiment, an X-ray tube can include: a cathode
including an electron emitter that emits an electron beam; an anode
configured to receive the emitted electrons of the electron beam; a
first magnetic quadrupole between the cathode and the anode and
having a first quadrupole yoke with four first quadrupole pole
projections extending from the first quadrupole yoke and oriented
toward a central axis of the first quadrupole yoke and each of the
four first quadrupole pole projections having a first quadrupole
electromagnetic coil; a second magnetic quadrupole between the
first magnetic quadruple and the anode and having a second
quadrupole yoke with four second quadrupole pole projections
extending from the second quadrupole yoke and oriented toward a
central axis of the second quadrupole yoke and each of the four
second quadrupole pole projections having a second quadrupole
electromagnetic coil; and a magnetic dipole between the cathode and
anode and having a dipole yoke with four dipole electromagnetic
coils.
[0302] In one embodiment, an X-ray tube can include: the first
magnetic quadrupole being configured for providing a first magnetic
quadrupole gradient for focusing the electron beam in a first
direction and defocusing the electron beam in a second direction
orthogonal to the first direction; the second magnetic quadrupole
being configured for providing a second magnetic quadrupole
gradient for focusing the electron beam in the second direction and
defocusing the electron beam in the first direction; and wherein a
combination of the first and second magnetic quadrupoles provides a
net focusing effect in both first and second directions of a focal
spot of the electron beam. In one aspect, the magnetic dipole can
be configured to deflect the electron beam in order to shift the
focal spot of the electron beam on a target. In one aspect, the
magnetic dipole has the dipole yoke with four dipole pole
projections extending from the dipole yoke that are oriented toward
a central axis of the dipole yoke and each of the four dipole pole
projections have one of the dipole electromagnetic coils. In one
aspect, the four dipole magnetic coils are wrapped around the
dipole yoke in an even distribution. In one aspect, the magnetic
dipole can have the dipole yoke with four dipole pole projections
extending from the dipole yoke and oriented toward a central axis
of the dipole yoke, and the dipole magnetic coils are between the
dipole pole projections
[0303] In one embodiment, the four first quadrupole pole
projections having the first quadrupole electromagnetic coils are
at 45, 135, 225, and 315 degrees; the four second quadrupole pole
projections having the second quadrupole electromagnetic coils are
at 45, 135, 225, and 315 degrees; and the four dipole
electromagnetic coils are at 0, 90, 180, and 270 degrees.
[0304] In one embodiment, the four first quadrupole pole
projections having the first quadrupole electromagnetic coils are
at 45, 135, 225, and 315 degrees; the four second quadrupole pole
projections having the second quadrupole electromagnetic coils are
at 45, 135, 225, and 315 degrees; and the four dipole
electromagnetic coils are at 45, 135, 225, and 315 degrees.
[0305] In one embodiment, the X-ray tube has the following order
along the emitted electrons: cathode; first magnetic quadrupole
(cathode quadrupole); second magnetic quadrupole (anode
quadrupole); magnetic dipole; and anode.
[0306] In one embodiment, the electron emitter has a substantially
planar surface configured to emit electrons in an electron beam in
a non-homogenous manner.
[0307] In one embodiment, the first magnetic quadrupole can be
operably coupled with a first focus power supply; the second
magnetic quadruple can be operably coupled with a second focus
power supply; a first dipole pair of the magnetic dipole can be
operably coupled with a first steering power supply; and a second
dipole pair of the magnetic dipole can be operably coupled with a
second steering power supply.
[0308] In one embodiment, the first magnetic quadrupole can be
operably coupled with a first focus power supply; the second
magnetic quadruple can be operably coupled with a second focus
power supply; and each electromagnet of the magnetic dipole can be
operably coupled with a different steering power supply.
[0309] In one embodiment, an X-ray tube can include: a cathode
including an emitter, wherein the emitter has a substantially
planar surface configured to emit electrons in an electron beam in
a non-homogenous manner; an anode configured to receive the emitted
electrons; a first magnetic quadrupole formed on a first yoke and
having a magnetic quadrupole gradient for focusing the electron
beam in a first direction and defocusing the electron beam in a
second direction perpendicular to the first direction; a second
magnetic quadrupole formed on a second yoke and having a magnetic
quadrupole gradient for focusing the electron beam in the second
direction and defocusing the electron beam in the first direction;
wherein a combination of the first and second magnetic quadrupoles
provides a net focusing effect in both first and second directions
of a focal spot of the electron beam; and a magnetic dipole
configured to deflect the electron beam in order to shift the focal
spot of the electron beam on a target, the magnetic dipole
configured on a dipole yoke that is separate and different from the
second yoke and/or the first and the second yoke.
[0310] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include: providing the X-ray
tube of one of the embodiments; operating the electron emitter so
as to emit the electron beam from the cathode to the anode along an
electron beam axis; operating the first magnetic quadrupole to
focus the electron beam in a first direction; operating the second
magnetic quadrupole to focus the electron beam in a second
direction orthogonal with the first direction; and operating the
magnetic dipole to steer the electron beam away from the electron
beam axis.
[0311] In one embodiment, a method of focusing and steering an
electron beam in an X-ray tube can include providing the X-ray tube
of one of the embodiments, and operating the electron emitter so as
to emit the electron beam from the cathode to the anode along an
electron beam axis, implementing one or more of the following:
operating the first magnetic quadrupole to focus the electron beam
in a first direction; operating the second magnetic quadrupole to
focus the electron beam in a second direction orthogonal with the
first direction; or operating the magnetic dipole to steer the
electron beam away from the electron beam axis.
[0312] The present disclosure is not to be limited in terms of the
particular embodiments described in this application, which are
intended as illustrations of various aspects. Many modifications
and variations can be made without departing from its spirit and
scope, as will be apparent to those skilled in the art.
Functionally equivalent methods and apparatuses within the scope of
the disclosure, in addition to those enumerated herein, will be
apparent to those skilled in the art from the foregoing
descriptions. Such modifications and variations are intended to
fall within the scope of the appended claims. The present
disclosure is to be limited only by the terms of the appended
claims, along with the full scope of equivalents to which such
claims are entitled. It is to be understood that this disclosure is
not limited to particular methods, reagents, compounds,
compositions or biological systems, which can, of course, vary. It
is also to be understood that the terminology used herein is for
the purpose of describing particular embodiments only, and is not
intended to be limiting.
[0313] With respect to the use of substantially any plural and/or
singular terms herein, those having skill in the art can translate
from the plural to the singular and/or from the singular to the
plural as is appropriate to the context and/or application. The
various singular/plural permutations may be expressly set forth
herein for sake of clarity.
[0314] It will be understood by those within the art that, in
general, terms used herein, and especially in the appended claims
(e.g., bodies of the appended claims) are generally intended as
"open" terms (e.g., the term "including" should be interpreted as
"including but not limited to," the term "having" should be
interpreted as "having at least," the term "includes" should be
interpreted as "includes but is not limited to," etc.). It will be
further understood by those within the art that if a specific
number of an introduced claim recitation is intended, such an
intent will be explicitly recited in the claim, and in the absence
of such recitation no such intent is present. For example, as an
aid to understanding, the following appended claims may contain
usage of the introductory phrases "at least one" and "one or more"
to introduce claim recitations. However, the use of such phrases
should not be construed to imply that the introduction of a claim
recitation by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim recitation to
embodiments containing only one such recitation, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an" (e.g., "a" and/or
"an" should be interpreted to mean "at least one" or "one or
more"); the same holds true for the use of definite articles used
to introduce claim recitations. In addition, even if a specific
number of an introduced claim recitation is explicitly recited,
those skilled in the art will recognize that such recitation should
be interpreted to mean at least the recited number (e.g., the bare
recitation of "two recitations," without other modifiers, means at
least two recitations, or two or more recitations). Furthermore, in
those instances where a convention analogous to "at least one of A,
B, and C, etc." is used, in general such a construction is intended
in the sense one having skill in the art would understand the
convention (e.g., "a system having at least one of A, B, and C"
would include but not be limited to systems that have A alone, B
alone, C alone, A and B together, A and C together, B and C
together, and/or A, B, and C together, etc.). In those instances
where a convention analogous to "at least one of A, B, or C, etc."
is used, in general such a construction is intended in the sense
one having skill in the art would understand the convention (e.g.,
"a system having at least one of A, B, or C" would include but not
be limited to systems that have A alone, B alone, C alone, A and B
together, A and C together, B and C together, and/or A, B, and C
together, etc.). It will be further understood by those within the
art that virtually any disjunctive word and/or phrase presenting
two or more alternative terms, whether in the description, claims,
or drawings, should be understood to contemplate the possibilities
of including one of the terms, either of the terms, or both terms.
For example, the phrase "A or B" will be understood to include the
possibilities of "A" or "B" or "A and B."
[0315] As will be understood by one skilled in the art, for any and
all purposes, such as in terms of providing a written description,
all ranges disclosed herein also encompass any and all possible
subranges and combinations of subranges thereof. Any listed range
can be easily recognized as sufficiently describing and enabling
the same range being broken down into at least equal halves,
thirds, quarters, fifths, tenths, etc. As a non-limiting example,
each range discussed herein can be readily broken down into a lower
third, middle third and upper third, etc. As will also be
understood by one skilled in the art all language such as "up to,"
"at least," and the like include the number recited and refer to
ranges which can be subsequently broken down into subranges as
discussed above. Finally, as will be understood by one skilled in
the art, a range includes each individual member. Thus, for
example, a group having 1-3 cells refers to groups having 1, 2, or
3 cells. Similarly, a group having 1-5 cells refers to groups
having 1, 2, 3, 4, or 5 cells, and so forth.
[0316] From the foregoing, it will be appreciated that various
embodiments of the present disclosure have been described herein
for purposes of illustration, and that various modifications may be
made without departing from the scope and spirit of the present
disclosure. Accordingly, the various embodiments disclosed herein
are not intended to be limiting, with the true scope and spirit
being indicated by the following claims.
* * * * *