U.S. patent application number 09/810589 was filed with the patent office on 2001-07-26 for electromagnet and magnetic field generating apparatus.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Hiramoto, Kazuo, Hirota, Junichi, Iwashita, Yoshihisa, Tadokoro, Masahiro, Umezawa, Masumi.
Application Number | 20010009267 09/810589 |
Document ID | / |
Family ID | 26400307 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009267 |
Kind Code |
A1 |
Tadokoro, Masahiro ; et
al. |
July 26, 2001 |
Electromagnet and magnetic field generating apparatus
Abstract
An electromagnet comprises a pair of magnetic pole 1a and 1b, a
return yoke 3, exciting coils 4 and 5, etc. In an interior portion
of a magnetic pole, plural spacers 2a-2g are provided putting side
by side in a horizontal direction. Each of the spaces 2a-2g is an
air layer and a longitudinal cross-section is a substantially
rectangular shape and the space has a lengthily extending slit
shape in a vertical direction against a paper face in FIG. 1. The
plural spaces are mainly arranged toward a right side from a beam
orbit center O and an interval formed between adjacent spaces is
narrower toward the right side. The electromagnet having a simple
magnetic pole structure and a wide effective magnetic field area in
a case where a maximum magnetic field strength is increased can be
secured.
Inventors: |
Tadokoro, Masahiro;
(Hitachioota-shi, JP) ; Hirota, Junichi;
(Hitachi-shi, JP) ; Hiramoto, Kazuo;
(Hitachioota-shi, JP) ; Umezawa, Masumi;
(Hitachi-shi, JP) ; Iwashita, Yoshihisa; (Uji-shi,
JP) |
Correspondence
Address: |
MATTINGLY, STANGER & MALUR, P.C.
104 E HUME AVE
ALEXANDRIA
VA
22301
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
26400307 |
Appl. No.: |
09/810589 |
Filed: |
March 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09810589 |
Mar 19, 2001 |
|
|
|
09070934 |
May 1, 1998 |
|
|
|
6236043 |
|
|
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Current U.S.
Class: |
250/298 |
Current CPC
Class: |
H05H 7/04 20130101; H01F
7/20 20130101; H01J 2237/152 20130101; H01J 37/1472 20130101 |
Class at
Publication: |
250/298 |
International
Class: |
H01J 049/30; B01D
059/44 |
Foreign Application Data
Date |
Code |
Application Number |
May 9, 1997 |
JP |
9-119057 |
Mar 11, 1998 |
JP |
10-59256 |
Claims
What is claimed is:
1. In an electromagnet for bending an orbit of a charged particle
beam according to a magnetic field which is generated between
magnetic poles; wherein said magnetic pole has at an interior
portion thereof an area which has a lower relative permeability
than that of a magnetic pole forming material.
2. An electromagnet according to claim 1; wherein said area having
said lower relative permeability is provided at an area which has a
relatively high magnetic flux density at said interior portion of
said magnetic pole.
3. An electromagnet according to claim 1; wherein said area having
said lower relative permeability is provided at an area which has a
relatively low magnetic flux density at said interior portion of
said magnetic pole.
4. An electromagnet comprises at least one pair of magnetic poles
which are arranged oppositely, a return yoke for forming a magnetic
path by connecting said magnetic poles each other, and a coil for
generating a magnetic field to vary an orbit of a charged particle
beam in a space formed between said magnetic poles; wherein said
magnetic pole has a space at an interior portion thereof.
5. An electromagnet according to claim 4; wherein said space is
provided at said relatively high magnetic flux density area in said
interior portion of said magnetic pole.
6. An electromagnet according to claim 4; wherein said space is
provided at said relatively low magnetic flux density area in said
interior portion of said magnetic pole.
7. An electromagnet comprises at least one pair of magnetic poles
which are arranged oppositely, a return yoke for forming a magnetic
path by connecting said magnetic poles each other, and a coil for
generating a magnetic field in a space to vary an orbit of a
charged particle beam between said magnetic poles; wherein a space
is provided at an interior portion of said magnetic pole to form
substantially homogeneously a magnetic field strength at a
predetermined area formed between said magnetic poles.
8. An accelerator comprises a first half accelerator for generating
a charged particle beam, a synchrotron for increasing an energy by
accelerating said charged particle beam, and a beam transportation
system which radiates said charged particle beam radiated from said
first half accelerator to said synchrotron; wherein said
synchrotron has an electromagnet in which an area having a lower
relative permeability than that of a magnetic pole forming material
is provided.
9. An accelerator according to claim 8; wherein said area having
said lower relative permeability is provided at an area which has a
relatively high magnetic flux density at said interior portion of
said magnetic pole.
10. An accelerator according to claim 8; wherein said area having
said lower relative permeability is provided at an area which has a
relatively low magnetic flux density at said interior portion of
said magnetic pole.
11. An accelerator comprises a first half accelerator for
generating a charged particle beam, a synchrotron for increasing an
energy by accelerating said charged particle beam, and a beam
transportation system which extracts said charged particle beam
radiated from said first half accelerator to said synchrotron;
wherein said synchrotron has an electromagnet in which a space is
provided at an interior portion of a magnetic pole to form
substantially homogeneously a magnetic field strength at a
predetermined area formed between said magnetic poles.
12. An accelerator according to any one of claims 8-11; wherein
said synchrotron comprises: an extracting device for extracting
said accelerated charged particle beam; and further a second beam
transportation system for transporting said extracted charged
particle beam which is radiated from said extracting crevice to a
beam application equipment.
13. An accelerator according to claim 12; wherein said beam
application equipment comprises a beam irradiation means for
irradiating said charged particle beam to an affected part of a
patient in an irradiation room.
14. A magnetic field generating apparatus comprises at least one
pair of pole pieces which are arranged oppositely by forming an air
gap, and a permanent magnet for supplying a magnetic flux to said
pole piece; wherein said pole piece has at an interior portion
thereof an area which has a lower relative permeability than that
of a pole piece forming material.
15. A magnetic field generating apparatus according to claim 14;
wherein said lower relative permeability area is a space.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to an electromagnet for
bending an orbit of a charged particle beam and a magnetic field
generating apparatus for generating a magnetic field in an air gap
and, in particularly to an electromagnet suitable for use in a
physical experimentation use accelerator, an industrial use
accelerator and a medical treatment use accelerator or a magnetic
field generating apparatus for use in a medical treatment use
diagnosing instrument such as MRI (Magnetic Resonance Imager).
[0003] 2. Prior Arts
[0004] In generally, an electromagnet used in an accelerator is
designed to have a desirable magnetic field distribution in a
predetermined area which is determined by a size of a charged
particle beam (hereinafter, it is called as a beam). However, in a
case when a magnetic field strength increases, due to an affect of
a magnetic saturation of an iron core which is used in a magnetic
pole of the electromagnet, a leakage magnetic field from the
magnetic pole increases. According to the affect of this leakage
magnetic field, since an area (hereinafter, it is called as a
preferable magnetic filed area) becomes narrow, where an amount of
a displacement from a desirable magnetic field distribution is less
than a predetermined value, in the electromagnet a maximum magnetic
field strength enable to use actually is limited.
[0005] For example, in a case of a bending electromagnet for use in
an accelerator, when a radius of curvature and a maximum magnetic
field strength are determined, a maximum energy of the beam
obtained by the accelerator is determined. As a result, in a case
where there is a chance of a use of the beam with a wide energy
range, since the maximum magnetic field strength of the
electromagnet is limited by the above stated reasons, it is
necessary to employ a bending electromagnet having a large radius
of curvature.
[0006] As to the prior art relating to the bending electromagnet, a
technique about a bending electromagnet is disclosed in Japanese
patent laid-open publication No. Hei 5-47,547 (hereinafter it is
called as a first prior art). In such a bending electromagnet, a
projection which is called as a magnetic pole shim is provided at
an end portion of magnetic poles which are arranged oppositely.
[0007] Further, recently it has paid to attention to a medical
treatment use diagnosing instrument using a magnetic field such as
an open type MRI, in which a permanent magnet having a flexibility
is utilized, and also it has studied about a method for generating
a high magnetic field and a good uniformity magnetic field in an
air gap.
[0008] In the magnetic field generating apparatus having the
permanent magnet, a conventional technique for generating the
magnetic field having the high magnetic field and the good
uniformity magnetic field is disclosed Japanese patent laid-open
publication No. Hei 5-243,037 (hereinafter, it is called as a
second prior art). This magnetic field generating apparatus
comprises pole pieces which are arranged oppositely and at an end
portion a magnetic pole shim is provided, and permanent
magnets.
[0009] Further, in this magnetic field apparatus, it is disclosed
about a central portion of the pole piece which is moved toward an
upper portion and a lower portion. A lateral cross-section of an
upper portion magnetic pole portion in this magnetic field
generating apparatus is shown in FIG. 12. In FIG. 12, 101 denotes a
permanent magnet, 103 denotes a yoke, 108 denotes a permanent
magnet fixing use bolt, and 121 and 122 denote pole pieces.
[0010] In the above stated first prior art, by concentrating a line
of magnetic force which spreads from an end portion of the magnetic
pole toward a lateral direction, it aims to spread a good field
region (stated in a latter portion) formed between the magnetic
poles.
[0011] However, since it is necessary to provide the projection to
the magnetic pole, a magnetic pole structure becomes a complicated
one. Further, since the magnetic field distribution formed between
the magnetic poles is affected largely by a shape of the
projection, it requires a high processing accuracy for
manufacturing the magnetic poles. In company with this, also a
manufacturing cost becomes high.
[0012] Further, in the above stated second prior art, similarly to
the first prior art, since it is necessary to provide the
projection to the pole piece, the pole piece structure becomes a
complicated one. Further, since the magnetic field distribution
formed between the pole pieces is affected largely by a shape of
the projection, it is required a high processing accuracy for the
pole piece.
[0013] Further, in the second prior art, since a movement mechanism
is provided by dividing into the pole piece, it requires a large
mechanical force to a mechanical sliding portion, a high
reliability, and a high reproducibility. In company with those
requirements, also a manufacturing cost becomes high.
[0014] On the other hand, in the defecting electromagnet in which a
projection is not provided to a magnetic pole, since a maximum
magnetic field strength is limited according to an affect of a
magnetic saturation, in a case where it aims to obtain a wide range
beam energy, the bending electromagnet becomes a large size one and
also the accelerator becomes a large size one. Similarly to, the
magnetic field generating apparatus in which the projection is not
provided at the pole piece becomes a large size one.
SUMMARY OF THE INVENTION
[0015] A first object according to the present invention is to
provide an electromagnet which has a simple structure and secures a
high magnetic field and a good uniformity magnetic field or a
magnetic field generating apparatus. Herein, the good magnetic
field having the uniformity property indicates that an effective
magnetic field area is wide. Further, the effective magnetic field
area, as stated in a latter portion, indicates to a magnetic field
area which can be used for bending an orbit of a beam in a
preferable magnetic field area.
[0016] A second object according to the present invention is to
provide an accelerator which has a wide beam energy range enable to
use and has a small size structure.
[0017] A first invention for attaining the first object is that in
an electromagnet for bending an orbit of a charged particle beam
according to a magnetic field which is generated between magnetic
poles, said magnetic pole has at an interior portion thereof an
area which has a lower relative permeability than that of a
magnetic pole forming material.
[0018] A second invention for attaining the first object is that an
electromagnet comprises at least one pair of magnetic poles which
are arranged oppositely, a return yoke for forming a magnetic path
by connecting said magnetic poles each other, and a coil for
generating a magnetic field to vary an orbit of a charged particle
beam in a space formed between said magnetic poles, said magnetic
pole has a space at an interior portion thereof.
[0019] A third invention for attaining the first object is that an
electromagnet comprises at least one pair of magnetic poles which
are arranged oppositely, a return yoke for forming a magnetic path
by connecting said magnetic poles each other, and a coil for
generating a magnetic field in a space to vary an orbit of a
charged particle beam between said magnetic poles, a space is
provided at an interior portion of said magnetic pole to form
substantially homogeneously a magnetic field strength at a
predetermined area formed between said magnetic poles.
[0020] A fourth invention for attaining the second object is that
an accelerator comprises a first half accelerator for generating a
charged particle beam, a synchrotron for increasing an energy by
accelerating said charged particle beam, and a beam transportation
system which injects said charged particle beam extracted from said
first half accelerator to said synchrotron, said synchrotron has an
electromagnet in which an area having a lower relative permeability
than that of a magnetic pole forming material is provided.
[0021] A fifth invention for attaining the second object is that an
accelerator comprises a first half accelerator for generating a
charged particle beam, a synchrotron for increasing an energy by
accelerating said charged particle beam, and a beam transportation
system which injects said charged particle beam extracted from said
first half accelerator to said synchrotron, said synchrotron has an
electromagnet in which a space is provided at an interior portion
of a magnetic pole to form substantially homogeneously a magnetic
field strength at a predetermined area formed between said magnetic
poles.
[0022] A sixth invention for attaining the first object is that a
magnetic field generating apparatus comprises at least one pair of
pole pieces which are arranged oppositely by forming an air gap,
and a permanent magnet for supplying a magnetic flux to said pole
piece, said pole piece has at an interior portion thereof an area
which has a lower relative permeability than that of a pole piece
forming material.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a longitudinal cross-sectional view showing a
first embodiment of an electromagnet according to the present
invention;
[0024] FIG. 2 is an analysis example showing a magnetic field
distribution according to the first embodiment;
[0025] FIG. 3 is an analysis example showing a magnetic field
distribution according to a first comparison example;
[0026] FIG. 4 is a desirable magnetic field strength according to
the first embodiment;
[0027] FIG. 5 is a longitudinal cross-sectional view showing a
second embodiment of an electromagnet according to the present
invention;
[0028] FIG. 6 is an analysis example showing a magnetic field
distribution according to the second embodiment;
[0029] FIG. 7 is an analysis example showing a magnetic field
distribution according to a second comparison example;
[0030] FIG. 8 is a longitudinal cross-sectional view showing a
third embodiment of an electromagnet according to the present
invention;
[0031] FIG. 9 is a schematic construction view showing a medical
treatment use accelerator using an electromagnet of a fourth
embodiment according to the present invention;
[0032] FIG. 10A is a longitudinal cross-sectional view showing an
electromagnet of a fifth embodiment according to the present
invention;
[0033] FIG. 10B is a lateral cross-sectional view showing the
electromagnet of the fifth embodiment according to the present
invention;
[0034] FIG. 11 is a lateral cross-sectional view showing an upper
portion magnetic pole portion of the fifth embodiment; and
[0035] FIG. 12 is a lateral cross-sectional view showing an upper
portion magnetic pole portion of a magnetic field generating
apparatus according to the prior art.
DESCRIPTION OF THE INVENTION
[0036] First Embodiment
[0037] Hereinafter, a first embodiment of an electromagnet
according to the present invention will be explained referring to
FIG. 1. FIG. 1 is a longitudinal cross-sectional view showing a
combined function bending magnet to which the present invention is
applied. This electromagnet has both functions about a bending
electromagnet (a two-pole electromagnet) and a quandrupole
electromagnet and it is assumed that the electromagnet is provided
on an orbit of an orbital fighting beam.
[0038] This electromagnet is constituted by a pair of magnetic pole
1a and magnetic pole 1b which are arranged oppositely by
sandwiching the orbit of the beam, a return yoke 3 for forming a
magnetic path by connecting the magnetic pole 1a and the magnetic
pole 1b, and exciting coils 4 and 5, etc.
[0039] In an interior portion of each of the magnetic pole 1a and
the magnetic pole 1b, plural spaces 2a-2g are provided by putting
side by side toward a horizontal direction (a lateral direction in
FIG. 1). This electromagnet is constituted symmetrically toward an
upper and lower portion against a horizontal plane (hereinafter, it
is called as an orbit horizontal plane) including a center O of the
beam orbit.
[0040] The return yoke 3 is divided into an upper side portion and
a lower side portion on the orbit horizontal plane. An upper side
return yoke 3 and the magnetic pole 1a constitute an upper portion
magnetic core as one body and further a lower side return yoke 3
and the magnetic pole 1b constitute a lower portion magnetic core
as one body. The upper portion magnetic core and the lower portion
magnetic core are constituted respectively by laminating thin plate
shape electromagnetic steel plates and they are combined each other
on the orbit plane.
[0041] A surface for opposing the magnetic pole 1a and the magnetic
pole 1b is constituted to have a different magnetic pole (N pole or
S pole) each other. For example, in a case where a surface of the
magnetic pole 1a is N pole, so as to form a surface of the magnetic
pole 1b as S pole, an electric current direction for flowing into
the exciting poles 4 and 5 is adjusted.
[0042] An interval in a vertical direction (an upper and lower
direction in FIG. 1) between the magnetic pole 1a and the magnetic
pole 1b is constituted to form wider toward a right side. Employing
the magnetic poles with the above stated construction, the electric
current is forced to flow into the exciting coils 4 and 5.
Accordingly, the magnetic field having a bending magnetic field
component and a quandrupole magnetic field component can be
generated in an area which includes the beam orbit between the
magnetic poles.
[0043] The respective interior portion of the spaces 2a 2g is an
air layer and forms a lower relative permeability area than that of
the magnetic pole forming material. The respective spaces 2a-2g has
a similar shape and a longitudinal cross-section is substantially
rectangular shape and has a slit like shape which extends lengthy
toward a vertical direction against a paper face in FIG. 1.
[0044] The plural spaces 2a-2g are arranged mainly near an area to
the surface of the magnetic pole toward the right side from the
center O of the beam orbit and an interval of the adjacent spaces
is formed narrower toward the right side. In this case, a right
side direction corresponds to an outer side direction of the
circulating beam orbit and a left side direction corresponds to an
inner side direction of the circulating beam orbit,
respectively.
[0045] An improvement effect of the magnetic field distribution of
the above stated first embodiment according to the present
invention will be explained referring to FIG. 2 and FIG. 3. FIG. 2
shows an analysis example of the magnetic field distribution
according to the first embodiment and FIG. 3 shows an analysis
example of a magnetic field distribution according to a first
comparison example where the spaces shown in FIG. 1 do not
exist.
[0046] In both of FIG. 2 and FIG. 3, a horizontal axis expresses a
horizontal direction distance from the beam orbit center O on the
orbit horizontal plane face in FIG. 1 and a vertical axis expresses
a relative value in which a difference between a required desirable
magnetic field strength in the electromagnet shown in FIG. 1 is
standardized using a desirable magnetic field strength.
[0047] Herein, the desirable magnetic field strength indicates a
magnetic field strength shown in FIG. 4. In other words, the
desirable magnetic field strength reduces monotonously in company
with the horizontal direction distance from the beam orbit center O
becomes large. In FIG. 4, a respective line of a real line, a dot
line and an one-dot chain line shows a respective magnetic field
strength on the beam orbit center O (hereinafter, it is called as a
center magnetic field strength) in cases of 0.8 T, 1.1 T and 1.2 T,
respectively.
[0048] In the cases of FIG. 2 and FIG. 3, for example, +50 mm in
the horizontal axis corresponds to a position separated from 50 mm
toward the right side from the beam orbit center O and further
+0.05% in the vertical axis corresponds to a generation of the
magnetic field strength which has 0.05% stronger magnetic field
strength than the desirable magnetic field strength.
[0049] In a case where the space does not exist in the magnetic
pole, as shown in FIG. 3, as far as the center magnetic field
strength B.sub.0 is 0.8 T, with a range of the horizontal direction
distance between -50 mm-+50 mm, the difference between the
desirable magnetic field having less than about .+-.0.02% can be
attained.
[0050] Namely, the preferable magnetic field area is an area of the
horizontal direction distance between -50mm-+50 mm. Hereinafter, a
right end and a left end of the preferable magnetic field area, an
area which is defined by a shorter distance from the beam orbit
center O is called as an effective magnetic field area in the
present specification.
[0051] For example, in the above stated example, since an upper
limit of the preferable magnetic field area is +55 mm and a lower
limit of the preferable magnetic field area is -50 mm, the shorter
distance from the beam orbit center is -50 mm. In this case, the
area having the horizontal direction distance of .+-.50 mm is
called as the effective magnetic field.
[0052] Since the beam orbits by vibrating the beam orbit center O
as a center, the effective magnetic field area is a magnetic field
area which can be utilized to vary the orbit of the beam.
Hereinafter, the effective magnetic field area is expressed using
Le.
[0053] In a case of FIG. 3, at B.sub.0=0.8 T, Le is about .+-.50
mm; at B.sub.0=1.1 T, Le is about .+-.10 mm; and at B.sub.0=1.2 T,
Le is about .+-.5 mm. Namely, between the center magnetic field
strength between from 0.8 T to 1.1 T, the effective magnetic field
area Le reduces abruptly.
[0054] In comparison with the above case shown in FIG. 3, as shown
in FIG. 2, in the case of this first embodiment according to the
present invention, so far as the center magnetic field strength of
1.35 T, the effective magnetic field area Le having about .+-.55 mm
can be attained. Namely, so far as a very strong magnetic field
strength in which the center magnetic field strength is 1.35 T, a
wide effective magnetic field area Le having about .+-.55 mm can be
realized.
[0055] The reasons for maintaining such a wide effective magnetic
field area Le having the above stated strong magnetic field
strength are as following. In the case of the electromagnet of this
first embodiment according to the present invention, as shown in
FIG. 4, in the left side of between the magnetic poles the more the
magnetic field strength is strong and at the right side of between
the magnetic poles the more the magnetic field strength is weak.
Namely, the more in the right side area in the magnetic pole the
more the magnetic flux density is low.
[0056] Accordingly, in a case where the center magnetic field
strength becomes strong, at the left side area in the magnetic pole
the magnetic saturation occurs. However at the right side area in
the magnetic pole since the magnetic flux density is low, there is
no affect due to the magnetic saturation. Namely, at the left side
and at the right side in the magnetic pole, since the balance of
the magnetic flux density is fallen apart largely, the effective
magnetic field area Le reduces largely. This is caused by a
nonlinear characteristic property of the magnetic saturation.
[0057] However, as shown in FIG. 1, in a case where plural spaces
are provided mainly at the right side area in the magnetic pole,
the magnetic flux at the right side area avoids a space where the
magnetic resistance is large but can pass through the area where a
relative permeability in the magnetic pole surrounding the space is
large.
[0058] As a result, the magnetic flux density mainly at the right
side area in the magnetic pole increases and the affect of the
magnetic saturation appears in the right side magnetic pole.
Namely, it is possible to make small the fall-in in balance (the
affect of the non-linear characteristic property of the magnetic
saturation) of the magnetic flux density at the right side and at
the left side in the magnetic pole. Accordingly, as shown in FIG.
2, the wide effective magnetic field area Le extending to the
strong magnetic field strength can be realized.
[0059] In this first embodiment according to the present invention,
since the projection of the magnetic pole shown in the conventional
technique is unnecessary, the magnetic pole structure can be
simplified. Further, since a high processing accuracy for the space
which is provided in the magnetic pole is unnecessary, and also a
manufacturing cost can be made cheaply.
[0060] As stated in above, in this first embodiment according to
the present invention, since the space is provided in the area in
which the magnetic flux density is low relatively in the magnetic
pole, the magnetic flux density at this area is increased and the
magnetic saturation effect is obtained at a whole magnetic poles,
therefore a predetermined effective magnetic field area can be
realized.
[0061] Further, in this first embodiment according to the present
invention, since the interval of the adjacent spaces is formed
narrower toward the right side, the increase of the magnetic flux
density at the right side area is performed more effectively.
[0062] Second Embodiment
[0063] Next, a second embodiment of an electromagnet according to
the present invention will be explained referring to FIG. 5. FIG. 5
is a longitudinal cross-sectional view showing a deflective
electromagnet in which the present invention is applied. This
electromagnet is assumed that the electromagnet is provided on an
orbit of a circulating charged particle beam.
[0064] This electromagnet is comprised of a pair of magnetic pole
1a and magnetic pole 1b which are arranged oppositely by
sandwiching the orbit of the charged particle beam, a return yoke 3
for forming a magnetic path by connecting the magnetic pole 1a and
the magnetic pole 1b, and exciting coils 4 and 5, etc. In an
interior portion of each of the magnetic pole 1a and the magnetic
pole 1b, two spaces 2a and 2b are provided at an area near a
surface of the magnetic pole by putting side and side toward a
horizontal direction (a lateral direction in FIG. 5). A horizontal
direction position of the respective spaces 2a and 2b is about -40
mm and about +40 mm by sandwiching a center O of the beam
orbit.
[0065] A surface for opposing the magnetic pole 1a and the magnetic
pole 1b of this second embodiment according to the present
invention is constituted to have a different magnetic pole (N pole
or S pole) each other similarly to that of the first embodiment
according to the present invention.
[0066] An upper and lower symmetric structure against the orbit
horizontal plane, an upper and lower division structure and a
laminated steel plate structure of this electromagnet of the this
second embodiment according to the present invention are similarly
to those of the first embodiment according to the present
invention.
[0067] The interior portion of each of the spaces 2a and 2b is an
air layer and forms an area of a lower relative permeability than
that of the magnetic pole forming material. Each of the space 2a
and the space 2b is formed with a similar shape and a longitudinal
cross-section of each of the space 2a and the space 2b is formed
with a substantially rectangular shape or a lace orbit shape and
also has a slit like shape which extends toward a vertical
direction against a paper face of FIG. 5.
[0068] An improvement effect of the magnetic field distribution of
this second embodiment according to the present invention will be
explained referring to FIG. 6 and FIG. 7. FIG. 6 shows an analysis
example of the this second embodiment according to the present
invention and FIG. 7 shows an analysis example of a second
comparison example in which the spaces of FIG. 5 is do not exist,
respectively.
[0069] In both of FIG. 6 and FIG. 7, a horizontal axis expresses a
horizontal direction distance from the center O of the beam orbit
in FIG. 5 and a vertical axis expresses a relative valve which is
standardized a difference between a required desirable magnetic
field strength in the electromagnet of FIG. 5 by the desirable
magnetic field strength.
[0070] The desirable magnetic field of this second embodiment
according to the present invention is an uniform magnetic field
distribution toward the horizontal direction. In FIG. 6 and FIG. 7,
a real line, a dot line and an one-dot chain line show cases where
the center magnetic field strength is 0.27 T, 1.33 T and 1.82 T,
respectively.
[0071] In a case of FIG. 7, at B.sub.0=0.27 T, the effective
magnetic field area Le is about .+-.60 mm; at B.sub.0=1.33 T, Le is
about .+-.50 mm; and at B.sub.0=1.82 T, Le is about .+-.10 mm.
Namely, between the center magnetic field strength from 1.33 T to
1.82 T, the effective magnetic field area Le reduces abruptly.
[0072] In comparison with the above case, in the case of this
second embodiment according to the present invention, as shown in
FIG. 6, so far as the center magnetic field strength of 1.82 T, the
effective magnetic field area Le having about .+-.55 mm can be
attained.
[0073] Namely, so far as a very strong magnetic field strength in
which the center magnetic field strength is 1.82 T, a wide
effective magnetic field area Le having about .+-.55 mm in the
horizontal direction distance can be realized.
[0074] The reasons of the above stated facts are as following. In a
case of FIG. 5, the magnetic flux density in the magnetic pole is
high at a right and left end portion areas but is low at a central
area. As shown in FIG. 5, when two spaces are provided at the area
in which the magnetic flux density is comparatively high in
comparison with the center of the magnetic pole, the magnetic flux
density in the inner side area becomes higher than those of the
spaces.
[0075] As a result, the substantially uniform magnetic flux density
can be obtained in the interior portion of the magnetic pole.
Accordingly, as shown in FIG. 6, the wide effective magnetic field
area Le extending the strong magnetic field strength, namely the
substantially uniform magnetic field area can be realized.
[0076] In this second embodiment according to the present
invention, with the same reasons stated in the first embodiment
according to the present invention, the magnetic pole structure can
be simplified and the manufacturing cost can be made cheaply.
Further, in this second embodiment according to the present
invention, a punching-out die for the laminated electromagnetic
steel plates can be simplified, it can be contributed to the cost
reduction for the electromagnet.
[0077] As stated in above, according to this second embodiment of
the present invention, since the spaces are provided in the area
where the magnetic flux density in the magnetic pole is relatively
high, the magnetic flux density of a surrounding area in the area
where the spaces are provided is increased, therefore a
predetermined effective magnetic field area can be realized.
[0078] Further, in the respective embodiments according to the
present invention, in a case where the magnetic pole structure is
allowed to form a little complicated one, it can provide the
conventional projection at the end portion of the magnetic pole. In
this case, the insurance for the wide effective magnetic field area
against the increase in the magnetic field strength can be attained
more effectively.
[0079] Third Embodiment
[0080] Next, a third embodiment according to the present invention
will be explained referring to FIG. 8. FIG. 8 is a longitudinal
cross-sectional view showing a quandrupole magnet in which the
present invention is applied. This electromagnet is assumed that
the electromagnet is provided on an orbit of a circulating charged
particle beam.
[0081] The electromagnet is comprised of two pairs of magnetic pole
1a and magnetic pole 1b which are arranged to be a point symmetry
against a center O of the beam orbit of the charged particle beam,
a return yoke 3 which forms a magnetic path by connecting adjacent
magnetic poles each other, and exciting coils 4 and 5, etc. In an
interior portion of the magnetic pole 1a and the magnetic pole 1b,
respective two spaces 2a and 2b are provided at a surrounding
portion of the central portion of the magnetic pole at an area near
to a surface of the magnetic pole.
[0082] The return yoke 3 is divided into an upper portion and a
lower portion on a horizontal plane of the orbit and further
divided into a right portion and a left portion against a vertical
plane (herein after, it is called as an orbit vertical plane)
including a center O of the beam orbit. Each of the four divided
return yoke and each of the magnetic poles are formed with an
integral structure and accordingly as shown in FIG. 8 four magnetic
cores are constituted. Each of the magnetic cores is constituted by
laminating thin plate like steel plates and is combined with on the
orbit horizontal plane and the orbit vertical plane.
[0083] The surface of the magnetic pole 1a and the surface of the
magnetic pole 1b are formed to have a different magnetic pole (N
pole or S pole) each other. For example, when the surface of the
magnetic pole 1a is N pole, to form the surface of the magnetic
pole 1b as S pole, an electric current direction for flowing into
the exciting coils 4 and 5 is adjusted. As a result, N pole and S
pole are arranged alternatively, a quandrupole magnetic field is
formed on the beam orbit.
[0084] An interior portion of each of the spaces 2a and 2b is an
air layer and forms a lower relative permeability than that of the
magnetic pole forming material. The spaces 2a and 2b have the same
shape and a vertical cross-section is a substantial circular shape
and against toward a paper face in FIG. 8 the space has a lengthy
extending column like shape.
[0085] In a case of this third embodiment according to the present
invention, an interval formed adjacent magnetic poles is narrower
toward an end portion of the magnetic pole, a magnetic field
strength formed between the magnetic poles becomes stronger near an
end portion of the magnetic pole. Namely, a magnetic flux in the
magnetic pole becomes higher toward an end portion of an area.
[0086] As shown in FIG. 8, in a case that the space is provided at
an area where the magnetic flux has a comparative high in
comparison with that of a magnetic pole center, the magnetic flux
having passed this space passes through a central area in the
magnetic pole which exists toward an inner side from the space and
where a magnetic resistance is low. As a result, the magnetic flux
in the central area existed toward the inner side from the space
increases.
[0087] Accordingly, in this third embodiment according to the
present invention, similarly to that of the first embodiment
according to the present invention, a wide effective magnetic field
area having a strong magnetic field strength can be realized.
However, in this third embodiment according to the present
invention, the quandrupole magnetic pole component generated by the
electromagnet is regulated according to a magnetic field gradient.
Further, with the same reasons stated in the first embodiment
according to the present invention, a magnetic pole structure can
be simplified and also a manufacturing cost can be made
cheaply.
[0088] As stated in the above, according to this third embodiment
of the present invention, since the space is provided at the area
where the magnetic flux in the magnetic pole is comparatively high,
the magnetic flux of a surrounding area on which the space is
provided is increased, a predetermined effective magnetic field
area can be realized.
[0089] Further, in the respective above stated embodiments
according to the present invention, the space is provided at the
area where the magenta flux is comparatively high or the area where
the magnetic flux is comparatively low, however in a case where the
space is suitably provided at both areas, the similar effect can be
obtained. Further, it is effective to provide the space at the area
near the magnetic surface in the magnetic pole, further it is
effective to arrange suitably more than two plural spaces.
[0090] Further, in place of the laminated electromagnetic steel
plate, an iron block can be used in the magnetic pole and in this
case the similar effect can be obtained. Further, in place of the
space, it can provide an area where a lower relative permeability
material than that of an iron system material for constituting the
magnetic pole is filled up.
[0091] The above stated concepts can be applied to an electromagnet
for generating a multi-pole magnetic field having more than
sexterpole.
[0092] Fourth Embodiment
[0093] Next, a fourth embodiment of a medical treatment use
accelerator system using the electromagnet according to the present
invention will be explained referring to FIG. 9. FIG. 9 is a
schematic construction view showing the medical treatment use
accelerator system.
[0094] The medical treatment use accelerator system comprises a
first half accelerator 10, a low energy beam transportation system
20, a synchrotron 30, a high energy beam transportation system 40,
a beam irradiation means 50, a power supply means for supplying an
electricity to those means, and a control means (not shown in
figure) for carrying out a respective control and a coordinated
control for those means, etc.
[0095] The low energy beam transportation system 20 injects a beam
having a low energy, which is extracted from the first half
accelerator 10, to the synchrotron 30. The synchrotron 30
accelerates the injected beam having the low energy to a beam
having a high energy. The high energy beam transportation system 40
transports the high energy beam extracted from the synchrotron 30
to the beam irradiation means 50. The beam irradiation means 50
radiates the high energy beam to an affected part of a patient 60
in an irradiation room (not shown in figure).
[0096] The low energy beam transportation system 20 comprises a
quandrupole electromagnets 21 and 22, and a bending electromagnet
23, etc. The quandrupole electromagnet 21 generates a magnetic
field for focusing the beam to a horizontal direction and on the
other hand the quandrupole electromagnet 22 generates a magnetic
field for converging the beam to a vertical direction, for example.
The bending electromagnet 23 deflects the beam in a horizontal
plane.
[0097] The synchrotron 30 comprises an injecting device 31,
quandrupole electromagnets 32 and 33, a bending electromagnet 34, a
sexterpole electromagnet 35, a high frequency accelerating cavity
36, an extracting device 37, etc. The injecting device 31 injects a
low energy beam extracted from the quandrupole electromagnet to the
synchrotron 30.
[0098] The quandrupole electromagnet 32 generates a magnetic field
for converging the beam to a horizontal direction and on the other
hand the quandrupole electromagnet 33 generates a magnetic field
for converging the beam to a vertical direction, for example. The
bending electromagnet 34 deflects the beam in a horizontal plane
(an orbit horizontal plane of a circulating beam).
[0099] The high frequency accelerating cavity 36 accelerates the
beam by applying the high frequency magnetic field to the
circulating beam. The extracting device 37 extracts from the
synchrotron 30 a beam accelerated by the high frequency
accelerating cavity 36. In this case, by applying the sexterpole
magnetic field to the beam which circulates from the sexterpole
electromagnet 35, accordingly the beam extraction is assisted.
[0100] The high energy beam transportation system 40 comprises a
quandrupole electromagnets 41 and 42, and a bending electromagnet
43, etc. The quandrupole electromagnet 41 generates a magnetic
field for converging the beam to a horizontal direction and on the
other hand the quandrupole electromagnet 42 generates a magnetic
field for converging the beam to a vertical direction, for example.
The bending electromagnet 43 deflects the beam in a horizontal
plane.
[0101] In this fourth embodiment according to the present
invention, as the electromagnet for the low energy beam
transportation system 20, a conventional electromagnet (a space
does not exist in a magnetic pole) is employed, and as to the
electromagnets for the synchrotron 30 and the high energy beam
transportation system 40, the electromagnet (the space exists in
the magnetic pole) according to the present invention is
employed.
[0102] Namely, the electromagnet according to the present invention
is employed to the quandrupole electromagnets 32 and 33 of the
synchrotron 30, the bending electromagnet 34, the sexterpole
electromagnet 35, the quandrupole electromagnets 41 and 42 for the
high energy beam transportation system 40, and the bending
electromagnet 43. For example, it can employ the electromagnet
shown in FIG. 5 as the bending electromagnet and also it can employ
the electromagnet shown in FIG. 8 as the quandrupole
electromagnet.
[0103] In a case of this fourth embodiment according to the present
invention, since the energy of the beam extracted from the first
half accelerator 10 is low and is substantially constant, it is
unnecessary to employ the electromagnet according to the present
invention to the low energy beam transportation system 20. On the
other hand, in the synchrotron 30, to accelerate the injected beam
to an energy necessary for an irradiation medical treatment, it
necessities a wide range center magnetic field strength,
accordingly the electromagnet according to the present invention is
employed.
[0104] Further, in the high energy beam transportation system 40,
in a case where the energy range of the radiated beam from the
synchrotron 30 is wide, namely so as to correspond to a case where
the energy of the beam radiated from the synchrotron 30 varies at a
short time and every an operation pulse each, the electromagnet
according to the present invention is employed.
[0105] According to the fourth embodiment of the present invention,
to the electromagnets for the synchrotron 30 and the high energy
beam transportation system 40, the electromagnet according to the
present invention is employed. In a case where a necessary maximum
beam energy is the same that of the prior art, it can form small
the electromagnet compared with that of the prior art, and it can
form with a small size the synchrotron 30 and the high energy beam
transportation system 40. Namely, it can form the medical treatment
use accelerator system with a small size.
[0106] Further, in a case where the sizes of the electromagnets for
the synchrotron 30 and the high energy beam transportation system
40 are same to those of the prior art, namely in a case where the
sizes of the synchrotron 30 and the high energy beam transportation
system 40 are same to those of the prior art, the maximum magnetic
field strength capable for generate in the electromagnet is larger
than that of the prior art. As a result, the maximum beam energy
obtained for the irradiation medical treatment use can be
heightened.
[0107] Further, in this fourth embodiment according to the present
invention, to both of the electromagnets for the synchrotron 30 and
the high energy beam transportation system 40, the electromagnet
according to the present invention is employed. However, in a case
where as only one of the electromagnets for the synchrotron 30 and
the high energy beam transportation system 40, the electromagnet
according to the present invention can be employed or in a case
where as only one of the bending electromagnet and the quandrupole
electromagnet the electromagnet according to the present invention
can be employed, each of the above cases the above stated effect
can be obtained in comparison with that of the prior art.
[0108] Further, as shown in this fourth embodiment according to the
present invention, the electromagnet according to the present
invention is not limited to apply to the medical treatment use
accelerator in which the beam taken out from the synchrotron is
utilized directly but also can apply to a general physical
experimentation use accelerator and an industrial use accelerator,
etc., and in those cases the similar effect can be obtained.
[0109] Further, the electromagnet according to the present
invention can apply to the bending electromagnet, the quandrupole
electromagnet and the sexterpole electromagnet and in addition to
those to can apply the various electromagnets such as an octapole
electromagnet, and a steering electromagnet, etc.
[0110] Fifth Embodiment
[0111] Next, MRI (Magnetic Resonance Imager) of one embodiment of a
magnetic field generating apparatus according to the present
invention will be explained referring to FIG. 10A, FIG. 10B and
FIG. 11. FIG. 10A and FIG. 10B are schematic construction views
showing MRI. FIG. 10A is a longitudinal cross-sectional view
showing MRI and FIG. 10B is a lateral cross-sectional view showing
MRI.
[0112] MRI comprises a pair of permanent magnets 101 which are
arranged oppositely by forming an air gap, a pair of pole pieces
120 which are provided at a side of the air gap of the permanent
magnet 101, a yoke 103 and four supporting stands 104 for combining
magnetically the permanent magnet 101 and the pole piece 120, a
permanent magnet fixing use bolt 108 for fixing the permanent
magnet 101, and an adjusting use bolt which is provided on an upper
portion of the four supporting stands 104 for adjusting a length of
the above stated air gap. The pole piece 120 has spaces 123.
Further, each of the yoke 103 and the supporting stand 104 is made
of a magnetic body.
[0113] Further, an upper portion magnetic pole portion of MRI will
be explained referring to FIG. 11. As shown in FIG. 11, the upper
portion magnetic pole portion comprises the permanent magnet 101,
the pole piece 120, the yoke 103 and the permanent magnet fixing
use bolt 108.
[0114] In FIG. 11, all of the magnetic fields generated from the
permanent magnet 101 are sucked in the pole piece 120 and the yoke
103, consequently the magnetic field generates from the pole piece
120 to the air gap. In this fifth embodiment according to the
present invention, to avoid a magnetic field concentration, an end
portion of the pole piece 120 is cut obliquely as shown in FIG. 11.
In a case where the end portion is cut obliquely, in generally
since a leakage of the magnetic flux is large, as a result a
homogenous magnetic field area becomes narrow.
[0115] However, in this fifth embodiment according to the present
invention, since the spaces 123 are provided in the pole piece 120,
the magnetic field is distributed to pass through by avoiding the
spaces 123, as a result, the magnetic flux of a center area flows
to an end portion area where the cut is performed.
[0116] Accordingly, the magnetic field leakage at the end portion
area is compensated and the homogenous magnetic field area is
widened. Further, the effect obtained by this fifth embodiment
according to the present invention is similar to the effect of the
embodiment shown in FIG. 5.
[0117] Further, since the leakage magnetic field becomes larger by
strengthening the magnetic field strength of the permanent magnet,
the magnetic flux distribution can be controlled by bending the
position of the spaces 123 to suit the maximum magnetic field
strength to be used. As a result, at the pole piece 120 a magnetic
saturation can be caused uniformly and a homogenous magnetic field
area can be generated regardless of the magnetic strength.
[0118] As stated in the above, according to the fifth embodiment of
the present invention, since the homogenous magnetic field area can
be obtained with the wide range, the upper portion magnetic pole
portion can form with a small size. Accordingly, MRI can form with
a small size.
[0119] According to the present invention, since the area (the
space) having the lower relative permeability compared with that of
the magnetic pole forming material is provided in the magnetic pole
of the electromagnet, with the simple magnetic pole structure, the
wide effective magnetic field area can be secured even in a case
where the maximum magnetic field strength is increased. Further, by
applying the above stated electromagnet to the accelerator, the
energy range of the beam capable for utilize can be widened with a
small size accelerator.
[0120] Further, according to the present invention, since the area
(the space) having the lower relative permeability compared with
that of the pole piece forming material is provided in the pole
piece of the magnetic field generating apparatus, with a simple
pole piece structure, the high magnetic field and the uniformity
property magnetic property can be secured.
* * * * *