U.S. patent application number 16/032333 was filed with the patent office on 2018-11-15 for electron beam generator and electron beam sterlizing device.
This patent application is currently assigned to TETRA LAVAL HOLDINGS & FINANCE S.A.. The applicant listed for this patent is TETRA LAVAL HOLDINGS & FINANCE S.A.. Invention is credited to Simone BIANCO, Dominique CLOETTA, Werner HAAG, Urs HOSTETTLER.
Application Number | 20180327126 16/032333 |
Document ID | / |
Family ID | 52629590 |
Filed Date | 2018-11-15 |
United States Patent
Application |
20180327126 |
Kind Code |
A1 |
CLOETTA; Dominique ; et
al. |
November 15, 2018 |
ELECTRON BEAM GENERATOR AND ELECTRON BEAM STERLIZING DEVICE
Abstract
Electron beam generator comprising an electron emitting device
adapted to emit an electron beam when heated to an elevated
temperature, wherein the electron emitting device comprises a
filament having a spiral portion.
Inventors: |
CLOETTA; Dominique;
(Villars-sur-Glane, CH) ; HOSTETTLER; Urs; (Thun,
CH) ; HAAG; Werner; (Lugnorre, CH) ; BIANCO;
Simone; (Bern, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TETRA LAVAL HOLDINGS & FINANCE S.A. |
Pully |
|
CH |
|
|
Assignee: |
TETRA LAVAL HOLDINGS & FINANCE
S.A.
Pully
CH
|
Family ID: |
52629590 |
Appl. No.: |
16/032333 |
Filed: |
July 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15127895 |
Sep 21, 2016 |
10046877 |
|
|
PCT/EP2015/054812 |
Mar 9, 2015 |
|
|
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16032333 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 29/04 20130101;
A61L 2202/23 20130101; B65B 55/08 20130101; H01J 33/02 20130101;
A61L 2/087 20130101; H01J 37/06 20130101; H01J 1/15 20130101; A61L
2202/11 20130101; A61L 2/26 20130101 |
International
Class: |
B65B 55/08 20060101
B65B055/08; H01J 37/06 20060101 H01J037/06; A61L 2/26 20060101
A61L002/26; A61L 2/08 20060101 A61L002/08; H01J 29/04 20060101
H01J029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2014 |
SE |
1450331-2 |
Claims
1. An electron beam generator comprising: an electron emitting
device adapted to emit an electron beam when heated to an elevated
temperature, and the electron emitting device comprising a filament
having a spiral portion, and a flat outer support element connected
to an outer end of the spiral filament and surrounding an outer
perimeter of the windings, wherein the outer support element
comprises at least three circumferentially spaced-apart connecting
points for mechanically and/or electrically connecting the electron
emitting device.
2. The electron beam generator according to claim 1, wherein the
electron emitting device is disc-shaped.
3. The electron beam generator according to claim 1, wherein a gap
is formed in the outer support element.
4. The electron beam generator according to claim 1, wherein the
filament comprises a plurality of windings, wherein a distance
between the windings in a radial direction is equal to or smaller
than a width in a radial direction of the windings.
5. The electron beam generator according to claim 1, wherein a
distance between an outer winding of the filament and the outer
support element is larger than a distance between adjacent windings
of the filament.
6. The electron beam generator according to claim 1, wherein the
filament comprises between three and eight windings.
7. The electron beam generator according to claim 1, wherein an
outer connecting portion of the filament where the filament is
connected to the outer support element is displaced in the
circumferential direction relative to an inner connecting portion
of the filament where the filament is connected to an inner support
element.
8. The electron beam generator according to claim 1, wherein the
filament comprises a connecting portion which merges into an inner
support element and/or the outer support element, wherein the
connecting portion comprises a bend between a radial and a
circumferential direction.
9. The electron beam generator according to claim 1, wherein the
spiral portion of the filament has a constant width along its
longitudinal extension.
10. The electron beam generator according to claim 1, wherein the
spiral portion of the filament has a varying width along its
longitudinal extension.
11. An electron beam generator comprising: an electron emitting
device adapted to emit an electron beam when heated to an elevated
temperature, and the electron emitting device comprising a filament
having a spiral portion, and a flat outer support element connected
to an outer end of the spiral filament and surrounding an outer
perimeter of the windings, wherein the outer support element
comprises at least one through-hole for mechanically and/or
electrically connecting the electron emitting device.
12. The electron beam generator according to claim 11, wherein the
electron emitting device is disc-shaped.
13. The electron beam generator according to claim 11, wherein a
gap is formed in the outer support element.
14. The electron beam generator according to claim 11, wherein the
filament comprises a plurality of windings, wherein a distance
between the windings in a radial direction is equal to or smaller
than a width in a radial direction of the windings.
15. The electron beam generator according to claim 11, wherein a
distance between an outer winding of the filament and the outer
support element is larger than a distance between adjacent windings
of the filament.
16. The electron beam generator according to claim 11, wherein the
filament comprises between three and eight windings.
17. The electron beam generator according to claim 11, wherein an
outer connecting portion of the filament where the filament is
connected to the outer support element is displaced in the
circumferential direction relative to an inner connecting portion
of the filament where the filament is connected to an inner support
element.
18. The electron beam generator according to claim 11, wherein the
filament comprises a connecting portion which merges into an inner
support element and/or the outer support element, wherein the
connecting portion comprises a bend between a radial and a
circumferential direction.
19. The electron beam generator according to claim 11, wherein the
spiral portion of the filament has a constant width along its
longitudinal extension.
20. The electron beam generator according to claim 11, wherein the
spiral portion of the filament has a varying width along its
longitudinal extension.
Description
[0001] This application is a Continuation of U.S. application Ser.
No. 15/127,895 filed on Sep. 21, 2016, which is the National Stage
of International Application No. PCT/EP2015/054812 filed on Mar. 9,
2015, and claims the benefit of Swedish Application No. 1450331-2
filed on Mar. 21, 2014, the entire content of each of which is
incorporated by reference herein.
[0002] The invention relates to an electron beam generator and an
electron beam sterilizing device for sterilizing a packaging
container by electron beam irradiation.
[0003] It is common practice to pack food products and drugs,
including liquid and partly liquid products, in packaging
containers. Such packaging containers may for example be
manufactured from a laminate comprising at least one layer of paper
or paperboard and one or more barrier layers, for example an
aluminium foil and/or a polymer material, such as for example a
polyethylene layer.
[0004] In particular in the medical and food industry, packaging
containers are sterilized before they are filled with the product.
Thereby, microorganisms, such as bacteria, fungi, viruses and
spores, which may be present on a surface of the packaging
container, are eliminated.
[0005] A known method of sterilizing packaging containers is
through radiation by charge carriers, in particular electron beams.
A known electron beam sterilizing device comprises an electron beam
generator arranged in a vacuum housing which is provided with an
electron exit window. The electron beam generator comprises a
filament connected to an electrical power supply. When an
electrical current is fed through the filament, the electrical
resistance of the filament causes the filament to be heated to an
elevated temperature, such as in the order of 2000 K. This heating
causes the filament to emit a cloud of electrons. The electrons are
accelerated towards the electron exit window by means of a
high-voltage potential between a cathode near the filament and the
electron exit window (being the anode). Due to the high energy of
the electrons, the electrons pass through the electron exit window
towards a target area, i.e. a surface of the packaging container to
be sterilized.
[0006] There are electron beam sterilization devices, or emitters,
which can be lowered into a packaging container for sterilizing the
interior of the packaging container. A known electron beam
sterilizing device adapted for an interior sterilization of a
packaging container comprises a generally tubular housing adapted
to be at least partly inserted into a packaging container. The
electron exit window is arranged on a front end of the tubular
housing and has a generally circular shape. The filament is
arranged in the housing, i.e. the vacuum chamber, and generates an
electron beam which is then directed by means of a high voltage
potential towards the electron exit window.
[0007] A known filament for an electron beam sterilizing device is
ring-shaped. Such a ring-shaped filament generates a beam profile
having a central peak and a declining current density in a radial
direction. In this connection, the term "beam profile" relates in
particular to the beam intensity profile in a direction
perpendicular to the direction of propagation of the electron beam,
more particularly to the current intensity or current density along
the radius of the electron exit window.
[0008] In order to generate a more even or homogeneous beam
profile, it is known to place a beam-shaping grid between the
filament and the electron exit window in order to shape the
electron beam. A beam-shaping grid comprises a plurality of
openings and is in particular used for diffusing the electron beam
into a more uniform beam and for focusing the electron beam towards
the electron exit window.
[0009] An electron beam sterilizing device with an electron beam
shaping grid is disclosed in US 2011/0192986 A1. The grid is
connected to a voltage supply. By applying or not applying a
positive or negative voltage to the grid, the electrons formed at
the filament will exit the grid or not. The grid comprises at least
two operational portions in order to shape the beam profile.
[0010] It is an object of the present invention to provide an
electron beam generator and an electron beam sterilizing device
generating an electron beam having an essentially homogeneous beam
profile, in particular without using a control grid.
[0011] The object is solved according to the invention with an
electron beam generator according to claim 1 and an electron beam
sterilizing device according to claim 11. Preferred embodiments are
defined in the dependent claims and the following description, in
particular taken together with the attached drawings.
[0012] The electron beam generator comprises an electron emitting
device adapted to emit an electron beam when heated to an elevated
temperature, such as in the order of 2000 K, e.g. at least 1800 K.
The electron-emitting device has a substantially flat shape and
comprises a filament having a spiral portion, which preferably
extends between an outer portion and an inner portion of the flat
electron-emitting device.
[0013] The electron beam sterilizing device according to the
invention is adapted for sterilizing a packaging container, in
particular an interior of a packaging container, by electron beam
irradiation. The electron beam sterilizing device comprises a
housing enclosing an internal space, wherein the housing comprises
an electron exit window. An electron beam generator according to
the invention is arranged in the internal space for generating an
electron beam. The electron beam exits the housing through the
electron exit window for sterilizing the packaging container.
[0014] A first aspect of the invention is to provide an electron
emitting device, which can also be described as generally
disc-shaped. The electron emitting device is preferably a
substantially circular plate having free spaces formed therein. The
disc-shaped electron emitting device preferably has a thickness
max. 0.3 mm, preferably max. 0.2 mm. The thickness is preferably
homogenous (except for any through-going slit or opening). A
diameter of the electron-emitting device is preferably at least 1
cm, more preferably in the order of a few centimetres, such as
between 1.5 cm and 5 cm.
[0015] A second aspect of the invention is to provide a spiral
filament within the disc-shaped electron emitting device. In other
words, the disc-shaped electron emitting device comprises a spiral
portion. The spiral portion (filament) itself has a flat shape,
i.e. not a circular cross-section, but a rectangular cross section.
The disc-shaped emitter preferably comprises a spiral slit formed
in the material of the disc, thereby forming the flat, spiral
filament in the disc-shaped electron emitting device.
[0016] The inventive electron emitting device can also be described
as a disc having at least one slit formed therein, such that on a
portion of the disc, a spiral filament is formed. The spiral
filament generates a substantially homogeneous beam profile and,
therefore, a homogeneous temperature at the electron exit
window.
[0017] In an embodiment of the invention, the electron emitting
device comprises a flat outer support element connected to an outer
end of the spiral filament. In other words, the spiral filament
does not extend over the entire radius of the flat electron
emitting device, but merges at its outer end into a support
element, which is preferably ring-shaped. This outer support
element, or support ring, may have a radial extension at least a
few times larger than the radial extension (width) of the windings
of the filament. Due to its size, and therefore its lower
temperature compared to the spiral portion of the electron beam
generator, the support ring normally does not emit electrons when
the electron beam generator is operated. In other words, the size
of the support ring is such that it does not emit electrons when
the electron beam generator is operated. During operation, an
electron current between 1 Milliampere (mA) and 10 mA, preferably 1
mA to 4 mA, is emitted by the electron emitting device, in
particular the filament. The electrical power applied to the
electron emitting device may be the order of 100 watts (W) to 400
W. In larger electron emitting devices an electron current between
4 mA and 6 mA may be emitted by the filament. The electrical power
applied is then about 300-500 W.
[0018] The outer support element, or support ring, is preferably
adapted to support the electron emitting device. In one embodiment
of the invention, the outer support element comprises at least one
connecting portion for mechanically and/or electrically connecting
the electron emitting device. For example, 1, 2, 3 or more
connecting portions may be provided at the outer support element.
The connecting portions are preferably distributed in a
circumferential direction on the outer support element. The
connecting portions may be any interface for mechanically mounting
a supporting structure, such as a supporting rod. For example, the
outer support element may have one or more apertures for connecting
(receiving) a supporting rod. Another alternative is to weld the
outer support element to the support housing in a number of points.
The inner support element may be welded to a pin connected to the
support housing.
[0019] In another embodiment of the invention, a gap is formed in
the outer support element. The gap, or hole, is preferably formed
in a portion of the outer support element adjacent to a connecting
portion of the filament, where the filament merges into, or
connects to, the outer support element. In particular, the gap may
be formed in a portion of the outer support element radially
outward of the outer connecting portion of the filament. The gap
formed in this area causes the temperature in an area of the outer
support element near the connecting portion of the filament to be
higher, due to less material in this area. This causes the beam
profile to not abruptly decline at the outer end of the spiral
filament. Therefore, a more homogeneous profile can be achieved, in
particular in a radially outer portion.
[0020] The gap may be formed as a slit which preferably extends in
the circumferential direction of the outer support element. The gap
forms, or generates, a rib-like structure between an inner border,
or edge, of the outer support element and the gap (opening) itself.
The length of the slit may be in the order of 10.degree. to
180.degree. , in particular 20.degree. to 60.degree..
[0021] In an embodiment of the invention, the filament comprises a
plurality of windings, wherein a distance between the windings in a
radial direction is equal to or smaller than a radial extension
(width) of the windings. In other words, the width of the windings
is equal to or larger than the width of the slits between the
windings. By minimizing the slit size, the uniformity of the beam
profile can be further enhanced.
[0022] In another embodiment of the invention, the distance between
an outer winding of the filament and the outer support element is
larger than a distance between adjacent windings of the
filament.
[0023] The filament may comprise 3 to 8 windings, in particular 3
to 6, 3 to 5 or 3 to 4 windings. If the number of windings
increases, the filament power necessary for a certain emission
current must be increased and the efficiency decreases therefore. A
preferred material of the electron-emitting device, in particular
the filament, is tungsten.
[0024] In an embodiment of the invention, an outer connection
point, or connecting portion, of the filament, where the filament
is connected to the outer support element, is displaced, in the
circumferential direction, relative to an inner connection point,
or portion, of the filament, where the filament is connected to an
inner support element. The circumferential offset of the connecting
points of the filament to the inner and outer support element
provides a more uniform beam profile in the circumferential
direction.
[0025] According to another embodiment, the filament comprises a
connecting portion, which merges into an inner support element
and/or an outer support element, wherein the connecting portion
comprises a bend, or curve, in particular between a radial and a
circumferential direction. In other words, the filament comprises a
spiral portion and a connecting portion, wherein the connecting
portion is arranged between the spiral portion and the inner
support element and/or the outer support element and comprises a
bend. Therefore, the spiral part of the filament does not merge
into the respective support element in a straight manner, but bends
towards the support element.
[0026] In another embodiment of the invention, the spiral portion
of the filament has a constant width along its longitudinal
extension. The constant width or constant radial extension further
provokes the homogeneous beam profile.
[0027] In another preferred embodiment, the electron-emitting
device comprises an inner, preferably flat support element
connected to an inner end of the filament. The inner support
element may have a radial extension at least a few times larger
than the radial extension (width) of the windings of the filament.
Due to its size, and therefore its lower temperature compared to
the spiral portion of the electron beam generator, the inner
support element normally does not emit electrons when the electron
beam generator is operated.
[0028] The inner support element is preferably adapted to support
the electron emitting device. In one embodiment of the invention,
the inner support element comprises at least one connecting portion
for mechanically and/or electrically connecting the electron
emitting device. The connecting portion may be any interface for
mechanically mounting a supporting structure, such as a supporting
rod, such as an aperture formed in the inner support element. The
inner support element may in particular be a support ring.
[0029] The inner support element is preferably disc-shaped or
ring-shaped. The inner support element may in particular be a whole
disc without slits. In another embodiment, a slit or hole may be
provided in the inner support element. The hole, in particular
through-hole, is preferably formed centrally in the inner support
element. The hole causes the temperature in an area of the outer
support element near the connecting portion of the filament to be
higher, so that the beam profile does not abruptly decline at the
inner end of the spiral filament. Therefore, a more homogeneous
profile can be achieved, in particular in a radially inner
portion.
[0030] According to another aspect of the invention, the electron
emitting filament is integrally formed with an inner support
element, in particular plate or ring, and an outer support element,
in particular ring, and exclusively supported by the inner and
outer support elements. Inner and outer support element and
filament may be formed together as a disc, preferably having a
constant thickness.
[0031] In one or more embodiments the spiral portion of the
filament has a varying width along its longitudinal extension. In
particular, in one or more embodiments at least an outer winding of
the spiral portion has a varying width along its longitudinal
extension. In this way the temperature can be adjusted for angular
sections of the filament in such a way that an electron beam is
achieved which is homogenous over the window, with only small
variations between angular sectors of the spiral portion, and with
a correct radial distribution of the electrons. The electron
emission, i.e. the amount of electron generated, within each
angular sector is similar. It will depend both on the emitting
surface area available and the temperature of that area.
[0032] In the following, the invention will be further described in
connection with the attached drawings, in which:
[0033] FIG. 1 shows a first embodiment of an electron beam
generator according to the invention.
[0034] FIG. 2 shows a beam profile generated by the electron beam
generator according to FIG. 1.
[0035] FIG. 3 shows a second embodiment of an electron beam
generator according to the invention.
[0036] FIG. 4 shows a side view of an embodiment of an electron
beam generator according to the invention.
[0037] FIG. 5 shows an electron beam sterilizing device according
to the invention comprising an inventive electron beam
generator.
[0038] FIG. 6 shows a cross section of the electron beam
sterilizing device of FIG. 5.
[0039] FIG. 7a shows a third embodiment of an electron beam
generator according to the invention.
[0040] FIG. 7b shows a portion of the embodiment of FIG. 7a, but in
an exaggerated version.
[0041] Equal or corresponding elements are denominated with the
same reference numerals in all figures. Features described in
connection with different figures can be combined as far as
technically possible.
[0042] FIG. 5 shows an electron beam sterilizing device 10
according to the invention for an interior sterilization of a
packaging container, in particular a food or drug container.
[0043] FIG. 6 shows a cross section of the electron beam
sterilizing device of FIG. 5.
[0044] In FIGS. 5 and 6 the electron beam sterilizing device 10 is
shown. The electron beam sterilizing device 10 comprises a housing
12 enclosing an internal space, in particular a vacuum space. The
housing 12, or vacuum chamber, has a substantially cylindrical
shape being axis-symmetric around longitudinal axis A. The housing
12 comprises a first housing portion 14, in which an inventive
electron beam generator 30 is positioned, and a cylindrical or
tubular second housing portion 16 adapted to be inserted into a
packaging container so as to sterilize an interior of the
container. An electron exit window 18 is formed on a front end of
the second housing portion 16, opposite the first housing portion
14. The electron exit window 18 comprises an electron transparent
foil 19 and a foil support member 20. An electron acceleration zone
is formed between the electron beam generator 30 and the electron
exit window 18, in particular within and along the second housing
portion 16. The acceleration zone is illustrated by the travelling
path of a single electron
[0045] The electron beam generator 30 arranged in the vacuum
housing 12, in particular the first housing portion 14, is adapted
to generate a cloud of electrons, which is accelerated towards the
electron exit window 18, when heated to an elevated temperature, in
particular in the order of 2000 K. Embodiments of the electron beam
generator 30 according to the invention will now be described with
reference to FIGS. 1 to 4.
[0046] FIG. 1 shows a first embodiment of an electron beam
generator 30 according to the invention. The electron beam
generator 30 comprises an electron emitting device 32 being
integrally formed in a flat, disc-like shape. The electron-emitting
device 32 may have a diameter of a few centimetres, such as at
least two, at least three or at least five centimetres. A thickness
of the electron-emitting device 32 can be in the range of 0.05
millimetres to 0.15 millimetres. Preferably, the thickness of the
electron-emitting device 32 is 0.2 millimetres or below. The
thickness may vary along the radius of the electron-emitting device
32, however, the thickness will generally be constant
throughout.
[0047] The electron-emitting device 32 comprises a filament 34 and
support elements 50, 60. The filament has a generally spiral shape.
The filament 34 comprises a plurality of windings 38. An outer
support element 50 surrounds the filament 34. The filament 34 is
connected to the outer support element 50 at the first, outer
connecting portion 42 disposed at a first (outer) end of the
filament 34. The outer support element 50 surrounds the filament 34
and is preferably integrally formed with the filament 34. Filament
34 and outer support element 50 are arranged in a common plane
(level).
[0048] A second longitudinal end (inner end) of the filament 34 is
connected to an inner support element 60 having a disc-like shape.
The inner support element 60 is preferably integrally formed with
the filament 34 and connected to the filament 34 at a second, inner
connecting portion 44. The filament 34, the outer support element
50 and the inner support element 60 are preferably made of
tungsten.
[0049] The outer support element 50 and the inner support element
60 are configured to support the filament 34 by connecting to the
respective longitudinal ends of the filament 34. The filament 34 is
preferably supported exclusively by the outer support element 50
and the inner support element 60. In other words, the filament 34
is only supported at its respective longitudinal ends. Due to the
size of the outer support element 50 and the inner support element
60, the temperature of the outer support element 50 and the inner
support element 60 will be significantly lower than the temperature
of the filament 34, in particular such that only a little or
basically no electrons are emitted by the outer support element 50
and the inner support element 60.
[0050] The filament 34 comprises a spiral portion 36 and a first
connecting portion 42 connecting to the outer support element 50
and a second connecting portion 44 connecting to the inner support
element 60. The first connecting portion 42 has a bend turning
towards the outside for connecting the spiral portion 36 to an
inner border 52 of the outer support element 50, which is in
particular circular. The second connecting portion 44 has a bend
turning towards the inside for connecting the spiral portion 36 to
an outer border 62 of the inner support element 60, which is in
particular circular.
[0051] The first connecting portion 42 is displaced in the
circumferential direction relative to the second connecting portion
44. In other words, the number of windings 38 of the filament 34 is
not an integer. The filament 34 includes a plurality of full
windings 38 and one fraction of a winding 38, wherein the fraction
is preferably between 20% and 80% of a full winding 38. In a
preferred embodiment, the displacement between the first connecting
portion 32 and the second connecting portion 44 in the
circumferential direction is between 45.degree. and 75.degree..
[0052] Between each of the windings 38, a free space, distance or
clearance 48 is formed. As can be seen in FIG. 1, the clearance 48
has a size approximately equal to the size of the windings 38. The
term "size" refers in this case in particular to the width, i.e.
the extension in the radial direction. For the distances or
clearances 48 the width is denoted d in the drawings, whereas for
the windings 38 the width is denoted w in the drawings. It may be
preferred that the size, i.e. the distance d, of the clearance 48,
is smaller than the size, i.e. the width w, of the windings 38.
[0053] A beam profile that can be achieved with the electron beam
generator 30 according to FIG. 1 is shown in FIG. 2. Because the
beam profile is substantially symmetrical with regard to the
central point of the electron beam generator 30, it is only shown
along a radius on the exit window. The origin is in the center of
the exit window. The graph represented in FIG. 2 refers to the dose
measured on the electron exit window 18 of an electron beam
sterilizing device 10. The centre of the electron-emitting device
32 is not emitting, because the temperature there is low. With
increasing distance from the centre, the temperature increases and
reaches its maximum value at a certain point of the filament 34
along its longitudinal extension. The temperature then decreases at
an end of the filament 34 close to the outer support element 50.
The decreased emission in the centre is a welcome effect, because
it compensates the electrons scattered towards the centre. The
intensity measured at the electron exit window 18 is essentially
homogeneous along the radius of the electron exit window 18 but
comprises a peak near the outer circumference of the electron exit
window 18.
[0054] The diameter of the spiral portion 36 determines the
diameter of the beam profile together with the design of the
housing 12, in particular the second housing portion 16 (snout). In
one embodiment the diameter of the filament 34 (corresponding to
the inner diameter of the outer support element 50) corresponds to
the diameter of the electron exit window 18. In other words, the
outer support element 50 has a diameter greater than the diameter
of the electron exit window 18.
[0055] The size of the clearances 48 between adjacent windings 38
(slit size) determines how much and how many electrons are
scattered and how much current from the back side of the
electron-emitting device 32 can get to the second housing portion
16 (tube). It has been found that the configurations shown in FIGS.
1 and 3 provide an advantageous configuration.
[0056] A second embodiment of an electron beam generator 30 is
shown in FIG. 3. The embodiment essentially corresponds to the
embodiment shown in FIG. 1 and only the differences will be
described. The outer support element 50 comprises a gap 54 (air
gap) which is located in a portion of the outer support element 50,
where the filament 34 merges into the outer support element 50. The
gap 54 is formed as a slit extending in the circumferential
direction, such that the filament 34 branches into two ribs, or
fins, 56. The size of these ribs 56 is such that a temperature is
higher than the temperature of the remaining outer support elements
50, when the electron beam generator 30 is operated. Therefore, the
temperature at the outer end of the filament 34 does not drop
abruptly at the point where it merges into the outer support
element 50. Preferably, the width of the ribs 56 essentially
corresponds to the width of the windings 38 of the filament 34. The
extension of the gap 54, or slit, in the circumferential direction
is between 45 and 135.degree., preferably, about 90.degree.. The
gap 54 is arranged in a portion radially outward of the first
connecting portion 42 of the filament 34, such that the filament 34
branches out at an outer end thereof In other words, the outer
support element 50 comprises two rib-like structures, adjacent the
first connecting portion 42 of the filament 34.
[0057] The inner support element 60 also comprises a gap, i.e. a
hole 64. The hole 64 is disposed in the centre of the inner support
element 60, such that the inner support element 60 has a circular
shape. The centre of the hole is aligned with the axis A. The
central hole of the inner support element 60 is used for a central
support bar 72, which will be described below. Due to the small
width at the second connecting portion 44, compared to the inner
support element 60, the temperature at the second connecting
portion 44 will be higher.
[0058] The disc-like electron emitting device 32 is supported by a
support structure 70, as shown in FIG. 4. The support structure 70
comprises a support housing 74 and a plurality of support bars, or
rods, 72. A central support bar 72 is connected to the inner
support element 60, and one or more outer support bars 72 are
connected to the outer support element 50. For the respective
connections, the outer support element 50 comprises one or more
connecting points 58 and the inner support element 60 comprises at
least one connecting point 68. The connecting points 58, 68 can be
holes in the outer support element 50 and the inner support element
60. An electrical connection for operating the electron beam
generator may be routed along, or through, the support bars 72.
This support structure 70 is valid for all the embodiments. Another
connection alternative is welding, i.e. the outer support element
is welded to the support housing in a number of points. In the
figure the disc-shaped electron emitting device 32 is planar, i.e.
the disc is planar, i.e. it extends in a plane. However, it should
be noted that the disc-shaped electron emitting device should be
positioned in the support structure in a way to get an optimal
configuration at operational temperatures. An optimal configuration
of the disc-shaped electron emitting device is not necessarily
perfectly planar. It may be necessary to position the disc-shaped
electron emitting device in a non-planar way in room temperature to
compensate for thermal dilatation at operational temperatures.
Hence, the disc-shaped electron emitting device may be positioned
in the support structure in a concave or convex manner.
[0059] A third embodiment of an electron emitting device 32 is
shown in FIGS. 7a and 7b. The electron emitting device in FIG. 7a
looks similar to the one in FIG. 3, and the electron emitting
device, of which only the spiral portion is shown, is similar to
FIG. 7a but a feature has been exaggerated for visibility. The
third embodiment essentially corresponds to the embodiment shown in
FIG. 3 and only the differences will be described. In the preceding
embodiments the spiral portion 36 has a constant width along the
longitudinal extension. In this embodiment the spiral portion has
instead a varying width along the longitudinal extension. In
particular, an outer winding 80, being the outermost winding of the
spiral portion 36, has a varying width along the longitudinal
extension. The variation of the width is not easily visible to the
human eye and is therefore hardly noticeable in FIG. 7a. However,
in FIG. 7b, the variation has been highly exaggerated for the
purpose of visability, and to facilitate description of the varying
width. The outer winding 80 is divided into angular sectors
a.sub.1, a.sub.2, a.sub.3 and a.sub.4 by the imaginary lines 1, 2,
3 and 4 shown in FIG. 7b.
[0060] At the first connection portion 42 the width is w.sub.0,
which is the starting width and the width of the rest of the
windings. The outer winding 80 in the first angular section a.sub.1
has this width, i.e. the width w.sub.0. In the second angular
section a.sub.2 the width is increasing. At the line 1 it is equal
to the width w.sub.0, but then the width is smoothly increasing to
the line 2, where the width is w.sub.0+dw. In the third angular
section a.sub.3 the width is constant and equal to w.sub.0+dw up to
the line 3. In the fourth angular section a.sub.4 the width
smoothly decreases back to w.sub.0 which has been reached at the
line 4.
[0061] The angle between line 1 and line 2 is about 120.degree.,
the angle between line 2 and line 3 is about 40.degree., the angle
between the line 3 and line 4 is about 100.degree. and the angle
between the line 4 and line 1 is about 100.degree.. It should be
understood that the variation of the width of the spiral portion
may be made in many ways, and that FIG. 7b only shows one
alternative out of many. The angles may be different and there may
be more or less angular sections. Further, the width may vary not
only in the outer winding but in any of the other windings. At the
same time the width in the outer winding may be constant.
[0062] In this embodiment a rib 56a, near the gap 54, has a larger
width than a rib 56b on the other side of the first connecting
point 42. The rib 56b is also near the gap 54. The width of the rib
56a is about twice as large as the width 56b.
Reference Numerals
[0063] 10 electron beam sterilizing device
[0064] 12 housing
[0065] 14 first housing portion
[0066] 16 second housing portion
[0067] 18 electron exit window
[0068] 19 foil
[0069] 20 foil support member
[0070] 30 electron beam generator
[0071] 32 electron emitting device
[0072] 34 filament
[0073] 36 spiral portion
[0074] 38 winding
[0075] 42 first connecting portion
[0076] 44 second connecting portion
[0077] 48 clearance
[0078] 50 outer support element
[0079] 52 inner border
[0080] 54 gap
[0081] 56 rib
[0082] 58 connecting point
[0083] 60 inner support element
[0084] 62 outer border
[0085] 64 hole
[0086] 68 connecting point
[0087] 70 support structure
[0088] 72 support bar
[0089] 74 support housing
[0090] 80 outer winding
* * * * *