BACKGROUND OF THE INVENTION
[0001] Electron beams are used in many industrial processes such as for drying or curing
inks, adhesives, paints and coatings. Electron beams are also used for liquid, gas
and surface sterilization as well as to clean up hazardous waste.
[0002] Conventional electron beam machines employed for industrial purposes include an electron
beam accelerator which directs an electron beam onto the material to be processed.
The accelerator has a large lead encased vacuum chamber containing an electron generating
filament or filaments powered by a filament power supply. During operation, the vacuum
chamber is continuously evacuated by vacuum pumps. The filaments are surrounded by
a housing having a grid of openings which face a metallic foil electron beam exit
window positioned on one side of the vacuum chamber. A high voltage potential is imposed
between the filament housing and the exit window with a high voltage power supply.
Electrons generated by the filaments accelerate from the filaments in an electron
beam through the grid of openings in the housing and out through the exit window.
An extractor power supply is typically included for flattening electric field lines
in the region between the filaments and the exit window. This prevents the electrons
in the electron beam from concentrating in the center of the beam as depicted in graph
1 of FIG. 1, and instead, evenly disperses the electrons across the width of the beam
as depicted in graph 2 of FIG. 1.
[0003] The drawback of employing electron beam technology in industrial situations is that
conventional electron beam machinery is complex and requires personnel highly trained
in vacuum technology and accelerator technology for maintaining the machinery. For
example, during normal use, both the filaments and the electron beam exit window foil
must be periodically replaced. Such maintenance must be done on site because the accelerator
is very large and heavy (typically 20 inches to 30 inches in diameter by 4 feet to
6 feet long and thousands of pounds).
[0004] Replacement of the filaments and exit window requires the vacuum chamber to be opened,
causing contaminants to enter. This results in long down times because once the filaments
and exit window foil are replaced, the accelerator must be evacuated and then conditioned
for high voltage operation before the accelerator can be operated. Conditioning requires
the power from the high voltage power supply to be gradually raised over time to burn
off contaminants within the vacuum chamber and on the surface of the exit window which
entered when the vacuum chamber was opened. This procedure can take anywhere between
two hours and ten hours depending on the extent of the contamination Half the time,
leaks in the exit window occur which must be remedied, causing the time of the procedure
to be further lengthened. Finally, every one or two years, a high voltage insulator
in the accelerator is replaced, requiring disassembly of the entire accelerator. The
time required for this procedure is about 2 to 4 days. As a result, manufacturing
processes requiring election beam radiation can be greatly disrupted when filaments,
electron beam exit window foils and high voltage insulators need to be replaced.
[0005] WO98 129895 discloses an electron accelerator as defined in the preamble of present claim 1.
An electron accelerator with an electron beam exit window membrane is also disclosed
in
US 5483074.
SUMMARY OF THE INVENTION
[0006] The present invention provides an electron accelerator as defined in present claim
1 and a method of manufacturing an electron accelerator as defined in present claim
10.
[0007] The present invention thereby provides a compact, less complex electron accelerator
for an electron beam machine which allows the electon beam machine to be more easily
maintained and does not require maintenance by personnel highly trained in vacuum
technology and accelerator technology.
[0008] In preferred embodiments, a series of openings in the housing forms the electrons
permeable region. The exit window membrane is preferably formed of titanium foil between
about 8 to 10 microns thick and is supported by a support plate having a series of
holes therethrough which allow the electrons to pass through. The configuration of
the holes in the support plate are arrangable to vary electron permeability across
the support plate for providing the electron beam with a desired variable intensity
profile. Topically, the exit window has an outer edge which is either brazed, welded
or bonded to the vacuum chamber to provide a gas tight seal therebetween.
[0009] The vacuum chamber includes an elongate ceramic member. In one preferred embodiments
the elongate ceramic member is corrugated which allows higher voltages to be used.
An annular spring member is coupled between the exit window and the corrugated ceramic
member to compensate for different rates of expansion.
[0010] In another preferred embodiment, the elongate ceramic member has a smooth surface
and a metallic shell surrounds the ceramic member. The ceramic member includes a frustoconical
hole which allows an electrical lead to extend through the frustoconical hole for
supplying power to the electron generator. A flexible insulating plug surrounds the
electrical lead and includes a frustoconical surface for sealing with the frustoconical
hole. A retaining cap is secured to the shell for retaining the plug within the frustoconical
bole.
[0011] The present invention provides a compact replaceable modular electron beam accelerator.
The entire accelerator is replaced when the filaments or the electron beam exit window
require replacing, thus drastically reducing the down time of an electron beam machine.
This also eliminates the need for personnel skilled in vacuum technology and electron
accelerator technology for maintaining the machine. In addition, high voltage insulators
do not need to be replaced on site. Furthermore, the inventive electron beam accelerator
has less components and requires less power than conventional electron beam accelerators,
making it less expensive, simpler, smaller and more efficient. The compact size of
the accelerator makes it suitable for use in machines where space is limited such
as in small printing presses, or for in line web sterilization and interstation curing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The foregoing and other objects, features and advantages of the invention will be
apparent from the following more particular description of preferred embodiments of
the invention, as illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views. The drawings are
not necessarily to scale, emphasis instead being placed upon illustrating the principles
of the invention.
FIG. 1 is a graph depicting the distribution of electrons in a focused electron beam
superimposed over a graph depicting the distribution of electrons in an electron beam
where the electrons are uniformly distributed across the width of the beam.
FIG. 2 is a side sectional schematic drawing of an electron beam accelerator not forming
part of the present invention.
FIG. 3 is a schematic drawing showing the power connections of the accelerator of
FIG. 2.
FIG. 4 is an end sectional view of the filament housing showing electric field lines.
FIG. 5 is an end sectional view of the filament housing showing electric field lines
if the side openings 35 are omitted.
FIG. 6 is a plan view of a system incorporating more than one electron beam accelerator.
FIG. 7 is a side sectional schematic drawing of the filament housing showing another
preferred method of electrically connecting the filaments.
FIG. 8 is a bottom sectional schematic drawing of FIG. 7.
FIG. 9 is a schematic drawing of another preferred filament arrangement.
FIG. 10 is another schematic drawing of still another preferred filament arrangement.
FIG. 11 is a side sectional view of another electron beam accelerator not forming
part of the present invention.
FIG. 12 is a side-sectional view of a preferred electron beam accelerator according
to the present invention
FIG. 13 is a side-sectional view of another preferred electron beam accelerator according
to the present invention
FIG. 14 is a bottom view of yet another preferred filament arrangement.
FIG. 15 is a plan view of a support plate with a pattern of holes filled to produce
an electron beam with a variable intensity profile across the beam.
FIG. 16 is a side view of an extension nozzle.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Referring to FIGs. 2 and 3, electron beam accelerator 10 not part of the present
invention is a replaceable modular accelerator which is installed in an electron beam
machine housing (not shown). Accelerator 10 includes an elongate generally cylindrical
two piece outer shell 14 which is sealed at both ends. The proximal end of outer shell
14 is enclosed by a proximal end cap 16 which is welded to outer shell 14. Outer shell
14 and end cap 16 are each preferably made from stainless steel but alternatively
can be made of other suitable metals.
[0014] The distal end of accelerator 10 is enclosed by an electron beam exit window membrane
24 made of titanium foil which is brazed along edge 23 to a stainless steel distal
end cap 20. End cap 20 is welded to outer shell 14. Exit window 24 is typically between
about 6 to 12 microns thick with about 8 to 10 microns being the more preferred range.
Alternatively, exit window 24 can be made of other suitable metallic foils such as
magnesium, aluminum, beryllium or suitable non-metallic low density materials such
as ceramics. In addition, exit window 24 can be welded or bonded to end cap 20. A
rectangular support plate 22 having holes or openings 22a for the passage of electrons
therethrough is bolted to end cap 20 with bolts 22b and helps support exit window
24. Support plate 22 is preferably made of copper for dissipating heat but alternatively
can be made of other suitable metals such as stainless steel, aluminum or titanium.
The holes 22a within support plate 22 are about 3.2mm (1/8 inch) in diameter and provide
about an 80% opening for electrons to pass through exit window 24. End cap 20 includes
a cooling passage 27 through which cooling fluid is pumped for cooling the end cap
20, support plate 22 and exit window 24. The cooling fluid enters inlet port 25a and
exits outlet port 25b. The inlet 25a and outlet 25b ports mate with coolant supply
and return ports on the electron beam machine housing. The coolant supply and return
ports include "0" ring seals for sealing to the inlet 25a and outlet 25b ports. Accelerator
10 is about 0.30m (12 inches) in diameter by 0.51m (20 inches) long and about 23kg
(50 pounds) in weight.
[0015] A high voltage electrical connecting receptacle 18 for accepting the connector 12
of a high voltage power cable is mounted to end cap 16. The high voltage cable supplies
accelerator 10 with power from a high voltage power supply 48 and a filament power
supply 50. High voltage power supply 48 preferably provides about 100 kv but alternatively
can be higher or lower depending upon the thickness of exit window 24. Filament power
supply 50 preferably provides about 15 volts. Two electrical leads 26a/26b extend
downwardly from receptacle 18 through a disk-shaped high voltage ceramic insulator
28 which divides accelerator 10 into an upper insulating chamber 44 and a lower vacuum
chamber 46. Insulator 28 is bonded to outer shell 14 by first being brazed to an intermediate
ring 29 made of material having an expansion coefficient similar to that of insulator
28 such as KOVAR®. The intermediate ring 29 can then be brazed to the outer shell
14. The upper chamber 44 is evacuated and then filled with an insulating medium such
as SF
6 gas but alternatively can be filled with oil or a solid insulating medium. The gaseous
and liquid insulating media can be filled and drained through shut off valve 42.
[0016] An electron generator 31 is positioned within vacuum chamber 46 and preferably consists
of three 8 inch long filaments 32 (FIG. 4) made of tungsten which are electrically
connected together in parallel. Alternatively, two filaments 32 can be employed. The
electron generator 31 is surrounded by a stainless steel filament housing 30. Filament
housing 30 has a series of grid like openings 34 along a planar bottom 33 and a series
of openings 35 along the four sides of housing 30. The filaments are preferably positioned
within housing 30 about midway between bottom 33 and the top of housing 30. Openings
35 do not extend substantially above filaments 32.
[0017] Electrical lead 26a and line 52 electrically connect filament housing 30 to high
voltage power supply 48. Electrical lead 26b passes through a hole 30a in filament
housing 30 to electrically connect filaments 32 to filament power supply 50. The exit
window 24 is electrically grounded to impose a high voltage potential between filament
housing 30 and exit window 24.
[0018] An inlet 39 is provided on vacuum chamber 46 for evacuating vacuum chamber 46. Inlet
39 includes a stainless steel outer pipe 36 which is welded to outer shell 14 and
a sealable copper tube 38 which is brazed to pipe 36. Once vacuum chamber 46 is evacuated,
pipe 38 is cold welded under pressure to form a seal 40 for hermetically sealing vacuum
chamber 46.
[0019] In use, accelerator 10 is mounted to an electron beam machine, and electrically connected
to connector 12. The housing of the electron beam machine includes a lead enclosure
which surrounds accelerator 10. Filaments 32 are heated up to about 4200°F by electrical
power from filament power supply 50 (AC or DC) which causes free electrons to form
on filaments 32. The high voltage potential between the filament housing 30 and exit
window 24 imposed by high voltage power supply 48 causes the free electrons 56 on
filaments 32 to accelerate from the filaments 32 in an electron beam 58 out through
openings 34 in housing 30 and the exit window 24 (FIG. 4).
[0020] The side openings 35 create small electric fields around the openings 35 which flatten
the high voltage electric field lines 54 between the filaments 32 and the exit window
24 relative to the plane of the bottom 33 of housing 30. By flattening electric field
lines 54, electrons 56 of electron beam 58 exit housing 30 through openings 34 in
a relatively straight manner rather than focusing towards a central location as depicted
by graph 1 of FIG. 1. This results in a broad electron beam 58 about 2 inches wide
by 8 inches long having a profile which is similar to that of graph 2 of FIG. 1. The
narrower higher density electron beam of graph 1 of FIG. 1 is undesirable because
it will burn a hole through exit window 24. To further illustrate the function of
side openings 35, FIG. 5 depicts housing 30 with side openings 35 omitted. As can
be seen, without side openings 35, electric field lines 54 arch upwardly. Since electrons
56 travel about perpendicularly to the electric field lines 54, the electrons 56 are
focused in a narrow electron beam 57. In contrast, as seen in FIG. 4, the electric
field lines 54 are flat allowing the electrons 56 to travel in a wider substantially
non-focusing electron beam 58. Accordingly, while conventional accelerators need to
employ an extractor power supply at high voltage to flatten the high voltage electric
field lines for evenly dispersing the electrons across the electric beam, the present
invention is able to accomplish the same results in a simple and inexpensive manner
by means of the openings 35.
[0021] When the filaments 32 or exit window 24 need to be replaced, the entire accelerator
10 is simply disconnected from the electron beam machine housing and replaced with
a new accelerator 10. The new accelerator 10 is already preconditioned for high voltage
operation and, therefore, the down time of the electron beam machine is merely minutes.
Since only one part needs to be replaced, the operator of the electron beam machine
does not need to be highly trained in vacuum technology and accelerator technology
maintenance. In addition, accelerator 10 is small enough and light enough in weight
to be replaced by one person.
[0022] In order to recondition the old accelerator 10, the old accelerator is preferably
sent to another location such as a company specializing in vacuum technology. First,
the vacuum chamber 46 is opened by removing the exit window 24 and support plate 22.
Next, housing 30 is removed from vacuum chamber 46 and the filaments 32 are replaced.
If needed, the insulating medium within upper chamber 44 is removed through valve
42. The housing 30 is then remounted back in vacuum chamber 46. Support plate 22 is
bolted to end cap 20 and exit window 24 is replaced. The edge 23 of the new exit window
24 is brazed to end cap 20 to form a gas tight seal therebetween. Since exit window
24 covers the support plate 22, bolts 22b and bolt holes, it serves the secondary
function of sealing over the support plate 22 without any leaks, "O"-rings or the
like. Copper tube 38 is removed and a new copper tube 38 is brazed to pipe 36. These
operations are performed in a controlled clean air environment so that contamination
within vacuum chamber and on exit window 24 are substantially eliminated.
[0023] By assembling accelerator 10 within a clean environment, the exit window 24 can be
easily made 8 to 10 microns thick or even as low as 6 microns thick. The reason for
this is that dust or other contaminants are prevented from accumulating on exit window
24 between the exit window 24 and the support plate 22. Such contaminants will poke
holes through an exit window 24 having a thickness under 12.5 microns. In contrast,
electron beam exit windows in conventional accelerators must be 12.5 to 15 microns
thick because they are assembled at the site in dusty conditions during maintenance.
An exit window 12.5 to 15 microns thick is thick enough to prevent dust from perforating
the exit window. Since the present invention exit window 24 is typically thinner than
exit windows on conventional accelerators, the power required for accelerating electrons
through the exit window 24 is considerably less. For example, about 150 kv is required
in conventional accelerators for accelerating electrons through an exit window 12.5
to 15 microns thick. In contrast, in the present invention, only about 80 kv to 125
kv is required for an exit window about 8 to 10 microns thick.
[0024] As a result, for a comparable electron beam, accelerator 10 is more efficient than
conventional accelerators. In addition, the lower voltage also allows the accelerator
10 to be more compact in size and allows a disk-shaped insulator 28 to be used which
is smaller than the cylindrical or conical insulators employed in conventional accelerators.
The reason accelerator 10 can be more compact then conventional accelerators is that
the components of accelerator 10 can be closer together due to the lower voltage.
The controlled clean environment within vacuum chamber 46 allows the components to
be even closer together. Conventional accelerators operate at higher voltages and
have more contaminants within the accelerator which requires greater distances between
components to prevent electrical arcing therebetween. In fact, contaminants from the
vacuum pumps in conventional accelerators migrate into the accelerator during use.
[0025] The vacuum chamber 46 is then evacuated through inlet 39 and tube 38 is hermetically
sealed by cold welding. Once vacuum chamber 46 is sealed, vacuum chamber 46 remains
under a permanent vacuum without requiring the use of an active vacuum pump. This
reduces the complexity and cost of operating the present invention accelerator 10.
The accelerator 10 is then preconditioned for high voltage operation by connecting
the accelerator 10 to an electron beam machine and gradually increasing the voltage
to burn off any contaminants within vacuum chamber 46 and on exit window 24. Any molecules
remaining within the vacuum chamber 46 are ionized by the high voltage and/or electron
beam and are accelerated towards housing 30. The ionized molecules collide with housing
30 and become trapped on the surfaces of housing 30, thereby further improving the
vacuum. The vacuum chamber 46 can also be evacuated while the accelerator 10 is preconditioned
for high voltage operation. The accelerator 10 is disconnected from the electron beam
machine and stored for later use.
[0026] FIG. 6 depicts a system 64 including three accelerators 10a, 10b and 10c which are
staggered relative to each other to radiate the entire width of a moving product 62
with electron beams 60. Since the electron beam 60 of each accelerator 10a, 10b, 10c
is narrower than the outer diameter of an accelerator, the accelerators cannot be
positioned side-by-side. Instead, accelerator 10b is staggered slightly to the side
and backwards relative to accelerators 10a and 10c along the line of movement of the
product 62 such that the ends of each electron beam 60 will line up with each other
in the lateral direction. As a result, the moving product 62 can be accumulatively
radiated by the electron beams 60 in a step-like configuration as shown. Although
three accelerators have been shown, alternatively, more than three accelerators 10
can be staggered to radiate wider products or only two accelerators 10 can be staggered
to radiate narrower products.
[0027] FIGs. 7 and 8 depict another preferred method of electrically connecting leads 26a
and 26b to filament housing 30 and filaments 32. Lead 26a is fixed to the top of filament
housing 30. Three filament brackets 102 extend downwardly from the top of filament
housing 30. A filament mount 104 is mounted to each bracket 102. An insulation block
110 and a filament mount 108 are mounted to the opposite side of filament housing
30. The filaments 32 are mounted to and extend between filament mounts 104 and 108.
A flexible lead 106 electrically connects lead 26b to filament mount 108. Filament
brackets 102 have a spring-like action which compensate for the expansion and contraction
of filaments 32 during use. A cylindrical bracket 112 supports housing 30 instead
of leads 26a/26b.
[0028] Referring to FIG. 9, filament arrangement 90 is another preferred method of electrically
connecting multiple filaments together in order to increase the width of the electron
beam over that provided by a single filament. Filaments 92 are positioned side-by-side
and electrically connected in series to each other by electrical leads 94.
[0029] Referring to FIG. 10, filament arrangement 98 depicts a series of filaments 97 which
are positioned side-by-side and electrically connected together in parallel by two
electrical leads 96. Filament arrangement 98 is also employed to increase the width
of the electron beam.
[0030] Referring to FIG. 11, accelerator 70 is another embodiment not forming part of the
present invention. Accelerator 70 produces an electron beam which is directed at a
90° angle to the electron beam produced by accelerator 10. Accelerator 70 differs
from accelerator 10 in that filaments 78 are parallel to the longitudinal axis A of
the vacuum chamber 88 rather than perpendicular to the longitudinal axis A. In addition,
exit window 82 is positioned on the outer shell 72 of the vacuum chamber 88 and is
parallel to the longitudinal axis A. Exit window 82 is supported by support plate
80 which is mounted to the side of outer shell 72. An elongated filament housing 75
surrounds filaments 78 and includes a side 76 having grid openings 34 which are perpendicular
to longitudinal axis A. The side openings 35 in filament housing 75 are perpendicular
to openings 34. An end cap 74 closes the end of the vacuum chamber 88. Accelerator
70 is suitable for radiating wide areas with an electron beam without employing multiple
staggered accelerators and is suitable for use in narrow environments. Accelerator
70 can be made up to about 3 to 4 feet long and can be staggered to provide even wider
coverage.
[0031] Referring to FIG. 12, accelerator 100 is a preferred embodiment of the present invention.
Accelerator 100 includes a generally cylindrical outer shell 102 formed of ceramic
material having a vacuum chamber 104 therein. Outer shell 102 has a closed proximal
end 106 and an open distal end 118 opposite thereof. The external surface of outer
shell 102 includes a series of corrugations 102a which allows accelerator 100 to run
at higher voltages than if outer shell 102 were smooth. The open end 118 has a region
with a smooth outer surface. A metallic end cap 110 surrounds and covers the smooth
open distal end 118 of outer shell 102 to enclose vacuum chamber 104.
[0032] End cap 110 is brazed to an intermediate annular metallic spring 108 which in turn
is brazed to outer shell 102, thereby sealing vacuum chamber 104. Spring 108 allows
the ceramic outer shell 102 and end cap 110 to expand and contract at different rates
in radial as well axial directions while maintaining a gas tight seal therebetween.
Spring 108 accomplishes this by spacing the end cap 110 slightly apart from outer
shell 102 as well as being formed of resilient material. Spring 108 includes an annular
inner V-shaped ridge 108a, the inner leg thereof brazed to outer shell 102. An annular
outer flange 108b extends radially outward from the V-shaped ridge 108a and is brazed
to end cap 110. End cap 110 includes an outer annular wall 112 and an inner annular
wall 114 with an annular gap 116 formed therebetween into which the open distal end
118 of outer shell 102 extends. Gap 116 is larger than the wall thickness of end 118
allowing end 118 to be spaced apart from the sides and bottom of gap 116, thereby
forming a space or passageway around end 118 as depicted by gaps 116a, 116b and 116c
to connect vacuum chamber 104 with inlet 39. This allows vacuum chamber 104 to be
evacuated via inlet 39. Inlet 39 is brazed or welded to, and extends through the outer
annular wall 112 of end cap 110. End cap 110 also includes a support plate 22 with
holes 22a extending therethrough. An exit window 24 is bonded over support plate 22
to end cap 112 typically under heat and pressure or brazing or welding. A cover plate
120 having a central opening 120a covers and protects exit window 24. End cap 110
has a cooling passage 27 which is similar to that depicted in FIG. 2. Although end
cap 110 is depicted as a single piece, end cap 110 can alternatively be formed of
multiple pieces. For example, support plate 22 and annular wall 114 can be separate
components. In addition, if desired, annular wall 114 can be omitted.
[0033] Filament housing 30 is positioned within vacuum chamber 104 just below the closed
proximal end 106 of outer shell 102. Electrical leads 26a/26b extend through and are
sealed to end 106 of outer shell 102. Filament housing 30 and electron generator 31
are similar to that depicted in FIG. 2. Although openings 35 are depicted in filament
housing 30, alternatively openings 35 can be omitted.
[0034] Referring to FIG. 13, accelerator 130 is another preferred accelerator of the present
invention. Accelerator 130 includes a metallic outer shell 122 surrounding a ceramic
inner shell 124 having a smooth external surface. The open end 118 of inner shell
124 preferably extends to support plate 22 thereby forming an annular wall 136 of
ceramic material between the vacuum chamber 134 and outer shell 122. Alternatively,
distal end 118 can terminate before reaching support plate 22. Inner shell 124 has
a frustoconical opening 124a extending through proximal end 119 opposite to distal
end 118. An electrical lead 128 having a connector 138 extends through frustoconical
hole 124a for providing power to filament housing 30 and electron generator 31 via
electrical leads 26a/26b. Filament housing 30 and electron generator 31 are similar
to that in accelerator 100 (FIG. 12). Electrical lead 128 also extends through the
central opening 126a of a flexible polymeric insulating plug 126. Insulating plug
126 includes a mating frustoconical outer surface 126b for sealing with the frustoconical
hole 124a. A retaining cap 140 secured to outer shell 122 exerts a compressive axial
force on plug 126 which compresses plug 126 against the converging surfaces of frustoconical
hole 124a and squeezes plug 126 around electrical lead 128 for sealing between electrical
lead 128 and inner shell 124. Preferably, plug 126 is made of ethylene propylene rubber
with an electrical resistance of 10
14 to 10
15 ohms-cm. Additionally, inner shell 124 preferably has an electrical resistance of
10
14 ohms-cm.
[0035] FIG. 14 depicts a preferred filament 32 for the electron generator 31 employed in
accelerators 100 and 130 (FIGs. 12 and 13). Filament 32 is formed with a series of
curves into a generally W shape. This allows filament 32 to expand and contract during
operation without requiring the support of resilient or spring-loaded components.
The ends of filament 32 can be bent in a hair pin turn as shown in FIG. 14 for insertion
through openings or slots within electrical leads 26a and 26b. If desired, more than
one filament 32 can be employed.
[0036] Referring to FIG. 15, if desired, the holes 22a of support plate 22 within accelerators
100 and 130 (FIGs. 12 and 13) can have a pattern of holes 142 that is filled or plugged
such that the resultant electron beam emitted has a variable intensity profile across
the beam. Alternatively, instead of filling or plugging holes 22a, the holes 22a can
be arranged within support plate 22 during manufacture to produce the desired pattern.
Although a particular pattern 142 has been depicted, any desirable pattern can be
formed.
[0037] Referring to FIG. 16, if desired, an extension nozzle 144 can be secured to accelerators
100 and 130 (FIGs. 12 and 13). In such a situation, the exit window 24 would be positioned
at the far end of nozzle 144. Nozzle 144 allows insertion within narrow openings such
as cups and bottles for sterilization therein.
[0038] The present invention electron accelerator is suitable for liquid, gas (such as air),
or surface sterilization as well as for sterilizing medical products, food products,
hazardous medical wastes and cleanup of hazardous wastes. Other applications include
ozone production, fuel atomization and chemically bonding or grafting materials together.
In addition, the present invention electron accelerator can be employed for curing
inks, coatings, adhesives and sealants. Furthermore, materials such as polymers can
be cross linked under the electron beam to improve structural properties.
[0039] The series of openings 35 in the filament housings form a passive electrical field
line shaper for shaping electrical field lines, in particular, a flattener for flattening
electrical field lines. The term "passive" meaning that the electrical field lines
are shaped without a separate extractor power supply. In addition, electrical field
lines can be shaped by employing multiple filaments. Furthermore, partitions or passive
electrodes can be positioned between the filaments for further shaping electrical
field lines. Multiple filaments, partitions or passive electrodes can be employed
as flatteners for flattening electrical field lines as well as other shapes.
[0040] While this invention has been particularly shown and described with references to
preferred embodiments thereof, it will be understood by those skilled in the art that
various changes in form and details may be made within the scope of the invention
as defined by the appended claims.
[0041] For example, although particular embodiments of the present invention have been described
to include multiple filaments, alternatively, only one filament can be employed. In
addition, although the outer shells (except ceramic outer shell 102), end caps and
filament housings are preferably made of stainless steel, alternatively, other suitable
metals can be employed such as titanium, copper or KOVAR®. End caps 16 and 20 are
usually welded to outer shell 14 but alternatively can be brazed. The holes 22a in
support plate 22 can be non-circular in shape such as slots. The dimensions of filaments
32 and the outer diameter of accelerator 10 can be varied depending upon the application
at hand. Also, other suitable materials can be used for insulator 28 such as glass.
Although the thickness of a titanium exit window is preferably under 12.5 microns
(between 6 and 12 microns), the thickness of the exit window can be greater than 12.5
microns for certain applications if desired. For exit windows having a thickness above
12.5 microns, high voltage power supply 49 should provide about 100 kv to 150 kv.
If exit windows made of materials which are lighter than titanium such as aluminum
are employed, the thickness of the exit window can be made thicker than a corresponding
titanium exit window while achieving the same electron beam characteristics. The accelerators
are preferably cylindrical in shape but can have other suitable shapes such as rectangular
or oval cross sections. Once the present invention accelerator is made in large quantities
to be made inexpensively, it can be used as a disposable unit. Receptacle 18 of accelerators
10 and 70 can be positioned perpendicular to longitudinal axis A for space constraint
reasons.
1. An electron accelerator comprising:
a vacuum vessel comprising a vacuum chamber (104,134) therein;
an electron beam exit window membrane (24) being formed of metallic foil (24) bonded
in metal to metal contact with the vacuum vessel to provide a gas tight seal therebetween,
the vacuum chamber being hermetically sealed to preserve a permanent self sustained
vacuum therein;
an electron generator (31) positioned in the vacuum chamber for generating electron;
and
a housing (30) surrounding the electron generator, the housing having an electron
permeable region formed in the housing between the electron generator and the exit
window membrane or allowing electrons to accelerate from the electron generator out
the exit window membrane in an electron beam when a voltage potential is applied between
the housing and the exit window membrane, characterized in that the vacuum vessel comprises an elongate ceramic member (102, 124) having a continuous
ceramic annular wall portion with an open end,
the electron beam exit window membrane (24) covers the open end and is supported by
a support plate (22) and wherein the exit window membrane is over the support plate,
and wherein the electron generator (31) positioned in the vacuum chamber is positioned
within the continuous ceramic annular wall portion of the vacuum vessel.
2. The accelerator of Claim 1 in which the elongate ceramic member is corrugated.
3. The accelerator of Claim 2 further comprising an annular spring member (108) bonded
to and between the exit window membrane and the ceramic member.
4. The accelerator of Claim 1 in which the vacuum vessel further comprises a metallic
shell (122) surrounding the ceramic member.
5. The accelerator of Claim 4 in which the ceramic member includes a frustoconical hole
(126a), the accelerator further comprising:
an electrical lead (128) extending through the frustoconical hole for supplying power
to the electron generator;
a flexible insulating plug (126) surrounding the electrical lead, the plug including
a frustoconical surface for sealing with the frustoconical hole; and
a retaining cap (140) secured to the shell for retaining the plug within the frustoconical
hole.
6. The accelerator of Claim 1 in which the electron permeable region comprises a series
of openings in the housing,
7. The accelerator of Claim 1 in which the exit window membrane is formed of titanium
foil having a thickness of between 8 to 10 microns.
8. The accelerator of Claim 1 wherein the support plate (22) has a series of holes therethrough
for allowing the electrons to pass through, the configuration of the holes being arrangable
to select electrons permeability across the support plate for providing the electron
beam with a variable intensity profile.
9. The accelerator at claim 1 in which the exit window membrane is formed of titanium
foil having a thickness of less than 12.5 microns.
10. A method of assembling an electron accelerator comprising the steps of:
providing a vacuum vessel comprising a vaccuum chamber (104, 134) therein and providing
an electron beam exit window membrane being formed of metallic foil bonded in metal
to metal contact with the vacuum vessel to provide a gas tight seal therebetween,
the vacuum chamber being hermetically sealed to preserve a self sustained vacuum therein;
providing an electron generator (31) positioned within the vacuum chamber; and
surrounding the electron generator with a housing (30), the housing having an electron
permeable region formed in the housing between the electron generator and the exit
window membrane for allowing electrons to accelerate from the electron generator out
the exit window membrane in an electron beam when a voltage potential is applied between
the housing and the exit window membrane, characterized in that the vacuum vessel comprises an elongate ceramic member (102, 124) having a continuous
ceramic annular wall portion with an open end, the electron beam exit window membrane
covering the open end and being supported by a support plate (22); and wherein the
exit window membrane is over the support plate, and wherein the electron generator
positioned in the vacuum chamber is positioned within the continuous ceramic annular
wall portion of the vacuum vessel.
11. The method of Claim (10) further comprising the step of providing the elongate ceramic
member with corrugations.
12. The method of Claim 11 further comprising the step of bonding an annular spring member
(108) to and between the exit window membrane and the ceramic member.
13. The method of Claim 10 further comprising the step of surrounding the ceramic member
with a metallic shell (122).
14. The method of Claim 13 in which the ceramic member includes a frustoconical hole(126a),
the method further comprising the steps of:
extending an electrical lead (128) through the frustoconical hole for supplying power
to the electron generator;
surrounding the electrical lead with a flexible insulating plug (126), the plug including
a frustoconical surface for sealing with the frustoconical hole; and
retaining the plug within the frustoconical hole with retaining cap (140) secured
to the shell.
15. The method of Claim 10, wherein the support plate has a series of holes therethrough
for allowing the electrons to pass through, the configuration of the holes being arrangable
to select electron permeability across the support plate for providing the electron
beam with a variable intensity profile.
16. The method at Claim 10 wherein the exit window membrane is formed of titanium foil
having a thickness of less than 12.5 microns.
1. Elektronenbeschleuniger umfassend:
einen Vakuumbehälter, der eine Vakuumkammer (104, 134) darin umfasst;
eine Elektronenstrahlaustrittsfenstermembrane (24), die aus Metallfolie (24) gebildet
ist, die in Metall-auf-Metall-Kontakt mit dem Vakuumbehälter verbunden ist, so dass
ein gasdichtes Siegel dazwischen bereitgestellt wird, wobei die Vakuumkammer hermetisch
versiegelt ist, so dass sie ein permanentes selbsterhaltendes Vakuum darin erhält;
einen Elektronengenerator (31), der in der Vakuumkammer zum Erzeugen von Elektronen
angeordnet ist; und
ein Gehäuse (30), das den Elektronengenerator umgibt, wobei das Gehäuse einen elektronendurchlässigen
Bereich aufweist, der in dem Gehäuse zwischen dem Elektronengenerator und der Austrittsfenstermembrane
ausgebildet ist, um zuzulassen, dass Elektronen von dem Elektronengenerator aus der
Austrittsfenstermembrane in einem Elektronenstrahl beschleunigen, wenn ein Spannungspotential
zwischen dem Gehäuse und der Austrittsfenstermembrane angelegt wird, dadurch gekennzeichnet, dass der Vakuumbehälter ein längliches Keramikelement (102, 124) umfasst, das einen durchgehenden,
keramischen, ringförmigen Wandungsbereich mit einem offenen Ende aufweist,
die Elektronenstrahlaustrittsfenstermembrane (24) das offene Ende abdeckt und durch
eine Stützplatte (22) gestützt wird und wobei die Austrittsfenstermembrane über der
Stützplatte ist, und wobei der Elektronengenerator (31), der in der Vakuumkammer angeordnet
ist, innerhalb des durchgehenden, keramischen, ringförmigen Wandungsbereichs des Vakuumbehälters
angeordnet ist.
2. Beschleuniger nach Anspruch 1, in welchem das längliche Keramikelement gewellt ist.
3. Beschleuniger nach Anspruch 2, des weiteren ein ringförmiges Federelement (108) umfassend,
das an und zwischen der Austrittsfenstermembrane und dem Keramikelement befestigt
ist.
4. Beschleuniger nach Anspruch 1, in welchem der Vakuumbehälter des weiteren einen metallischen
Mantel (122) umfasst, der das Keramikelement umgibt.
5. Beschleuniger nach Anspruch 4, in welchem das Keramikelement ein kegelstumpfförmiges
Loch (126a) umfasst, wobei der Beschleuniger des weiteren umfasst:
eine elektrische Anschlussleitung (128), die sich durch das kegelstumpfförmige Loch
erstreckt, um den Elektronengenerator mit Leistung zu versorgen;
einen flexiblen, isolierenden Pfropfen (126), der die elektrische Anschlussleitung
umgibt, wobei der Pfropfen eine kegelstumpfförmige Oberfläche umfasst, um das kegelstumpfförmige
Loch zu versiegeln; und
eine Haltekappe (140), die an dem Mantel befestigt ist, um den Pfropfen in dem kegelstumpfförmigen
Loch zu halten.
6. Beschleuniger nach Anspruch 1, in welchem der elektronendurchlässige Bereich eine
Reihe von Öffnungen in dem Gehäuse umfasst.
7. Beschleuniger nach Anspruch 1, in welchem die Austrittsfenstermembrane aus Titanfolie
mit einer Dicke zwischen 8 und 10 Mikrometern ausgebildet ist.
8. Beschleuniger nach Anspruch 1, bei welchem die Stützplatte (22) eine Reihe von Löchern
dadurch aufweist, um die Elektronen hindurchzulassen, wobei die Gestaltung der Löcher so
angeordnet werden kann, dass die Elektronendurchlässigkeit über die Stützplatte so
gewählt wird, dass der Elektronenstrahl mit einem variablen Intensitätsprofil versehen
ist.
9. Beschleuniger nach Anspruch 1, bei welchem die Austrittsfenstermembrane aus einer
Titanfolie mit einer Dicke von weniger als 12,5 Mikrometern ausgebildet ist.
10. Verfahren zum Zusammensetzen eines Elektronenbeschleunigers, umfassend:
Bereitstellen eines Vakuumbehälters, der eine Vakuumkammer (104, 134) darin umfasst,
und bereitstellen einer Elektronenstrahlaustrittsfenstermembrane, die aus Metallfolie
gebildet ist, die in Metall-auf-Metall-Kontakt mit dem Vakuumbehälter verbunden ist,
so dass ein gasdichtes Siegel dazwischen bereitgestellt wird, wobei die Vakuumkammer
hermetisch versiegelt ist, so dass sie ein selbsterhaltendes Vakuum darin erhält;
Bereitstellen eines Elektronengenerators (31), der in der Vakuumkammer angeordnet
ist;
Umgeben des Elektronengenerators mit einem Gehäuse (30), wobei das Gehäuse einen elektronendurchlässigen
Bereich aufweist, der in dem Gehäuse zwischen dem Elektronengenerator und der Austrittsfenstermembrane
ausgebildet ist, um zuzulassen, dass Elektronen von dem Elektronengenerator durch
die Austrittsfenstermembrane in einem Elektronenstrahl beschleunigen, wenn ein Spannungspotential
zwischen dem Gehäuse und der Austrittsfenstermembrane angelegt wird, dadurch gekennzeichnet, dass der Vakuumbehälter ein längliches Keramikelement (102, 124) umfasst, das einen durchgehenden,
keramischen, ringförmigen Wandungsbereich mit einem offenen Ende aufweist, wobei die
Elektronenstrahlaustrittsfenstermembrane das offene Ende abdeckt und durch eine Stützplatte
(22) gestützt wird; und wobei die Austrittsfenstermembrane über der Stützplatte ist,
und wobei der Elektronengenerator, der in der Vakuumkammer angeordnet ist, innerhalb
des durchgehenden, keramischen, ringförmigen Wandungsbereichs des Vakuumbehälters
angeordnet ist.
11. Verfahren nach Anspruch 10, des weiteren umfassend Ausstatten des länglichen Keramikelements
mit Wellen.
12. Verfahren nach Anspruch 11, des weiteren umfassend Verbinden eines ringförmigen Federelements
(108) mit und zwischen der Austrittsfenstermembrane und dem Keramikelement.
13. Verfahren nach Anspruch 10, des weiteren umfassend Umgeben des Keramikelements mit
einem metallischen Mantel (122).
14. Verfahren nach Anspruch 13, in welchem das Keramikelement ein kegelstumpfförmiges
Loch (126a) umfasst, wobei das Verfahren des weiteren umfasst:
Erstrecken einer elektrischen Anschlussleitung (128) durch das kegelstumpfförmige
Loch, um den Elektronengenerator mit Leistung zu versorgen;
Umgeben der elektrischen Anschlussleitung mit einem flexiblen, isolierenden Pfropfen
(126), wobei der Pfropfen eine kegelstumpfförmige Oberfläche umfasst, um das kegelstumpfförmige
Loch zu versiegeln; und
Halten des Pfropfens in dem kegelstumpfförmigen Loch mit einer Haltekappe (140), die
an dem Mantel befestigt ist.
15. Verfahren nach Anspruch 10, bei welchem die Stützplatte eine Reihe von Löchern dadurch aufweist, um die Elektronen hindurchzulassen, wobei die Gestaltung der Löcher so
angeordnet werden kann, dass eine Elektronendurchlässigkeit über die Stützplatte so
gewählt wird, dass der Elektronenstrahl mit einem variablen Intensitätsprofil versehen
ist.
16. Verfahren nach Anspruch 10, bei welchem die Austrittsfenstermembrane aus Titanfolie
mit einer Dicke von weniger als 12,5 Mikrometern ausgebildet ist.
1. Accélérateur d'électrons, comprenant :
un récipient sous vide comprenant une chambre à vide (104, 134) à l'intérieur de celui-ci
;
une membrane à fenêtre de sortie de faisceau d'électrons (24) formée en une feuille
métallique (24) fixée par contact métal-métal au récipient sous vide afin de réaliser
un joint d'étanchéité vis-à-vis des gaz entre ceux-ci, la chambre à vide étant hermétiquement
scellée de façon à préserver un vide auto-maintenu permanent à l'intérieur de celle-ci
;
un générateur d'électrons (21) positionné dans la chambre à vide pour générer des
électrons ; et
un boîtier (30) entourant le générateur d'électrons, le boîtier comportant une région
perméable aux électrons formée dans le boîtier entre le générateur d'électrons et
la membrane à fenêtre de sortie afin de permettre à des électrons d'accélérer à partir
du générateur d'électrons hors de la membrane à fenêtre de sortie sous la forme d'un
faisceau d'électrons lorsqu'un potentiel de tension est appliqué entre le boîtier
et la membrane à fenêtre de sortie, caractérisé en ce que le récipient sous vide comprend un élément en céramique allongé (102, 124) comportant
une partie de paroi annulaire en céramique continue avec une extrémité ouverte,
en ce que la membrane à fenêtre de sortie de faisceau d'électrons (24) recouvre l'extrémité
ouverte et est supportée par une plaque de support (22), la membrane à fenêtre de
sortie se trouvant sur la plaque de support, et le générateur d'électrons (31) positionné
dans la chambre à vide étant positionné à l'intérieur de la partie de paroi annulaire
en céramique continue du récipient sous vide.
2. Accélérateur selon la revendication 1, dans lequel l'élément en céramique allongé
est ondulé.
3. Accélérateur selon la revendication 2, comprenant de plus un élément de ressort annulaire
(108) fixé à la membrane à fenêtre de sortie et à l'élément en céramique et entre
ceux-ci.
4. Accélérateur selon la revendication 1, dans lequel le récipient sous vide comprend
de plus une enveloppe métallique (122) entourant l'élément en céramique.
5. Accélérateur selon la revendication 4, dans lequel l'élément en céramique comprend
un trou tronconique (126a), l'accélérateur comprenant de plus :
un conducteur électrique (128) s'étendant à travers le trou tronconique afin de délivrer
une alimentation au générateur d'électrons ;
un bouchon isolant souple (126) entourant le conducteur électrique, le bouchon comprenant
une surface tronconique pour réaliser une étanchéité avec le trou tronconique ; et
un capuchon de maintien (140) fixé à l'enveloppe afin de maintenir le bouchon à l'intérieur
du trou tronconique.
6. Accélérateur selon la revendication 4, dans lequel la région perméable aux électrons
comprend une série d'ouvertures dans le boîtier.
7. Accélérateur selon la revendication 1, dans lequel la membrane à fenêtre de sortie
est formée par une feuille de titane ayant une épaisseur comprise entre 8 et 10 micromètres.
8. Accélérateur selon la revendication 1, dans lequel la plaque de support (22) comporte
à travers celle-ci une série de trous afin de permettre aux électrons de la traverser,
la configuration des trous pouvant être agencée de façon à sélectionner une perméabilité
aux électrons à travers la plaque de support afin de communiquer au faisceau d'électrons
un profil d'intensité variable.
9. Accélérateur selon la revendication 1, dans lequel la membrane à fenêtre de sortie
est formée par une feuille de titane ayant une épaisseur inférieure à 12,5 micromètres.
10. Procédé d'assemblage d'un accélérateur d'électrons, comprenant les étapes consistant
à :
disposer un récipient sous vide comprenant une chambre à vide (104, 134) dans celui-ci,
et disposer une membrane à fenêtre de sortie de faisceau d'électrons formée par une
feuille métallique fixée en contact métal-métal au récipient sous vide afin de réaliser
un joint d'étanchéité vis-à-vis des gaz entre ceux-ci,
la chambre à vide étant hermétiquement scellée de façon à préserver un vide auto-maintenu
à l'intérieur de celle-ci ;
disposer un générateur d'électrons (31) positionné à l'intérieur de la chambre à vide
; et
entourer le générateur d'électrons par un boîtier (30), le boîtier comportant une
région perméable aux électrons formée dans le boîtier entre le générateur d'électrons
et la membrane à fenêtre de sortie afin de permettre à des électrons d'accélérer à
partir du générateur d'électrons hors de la membrane à fenêtre de sortie sous la forme
d'un faisceau d'électrons lorsqu'un potentiel de tension est appliqué entre le boîtier
et la membrane à fenêtre de sortie, caractérisé en ce que le récipient sous vide comprend un élément en céramique allongé (102, 124) comportant
une partie de paroi annulaire en céramique continue avec une extrémité ouverte, en ce que la membrane à fenêtre de sortie de faisceau d'électrons recouvre l'extrémité ouverte
et est supportée par une plaque de support (22), la membrane à fenêtre de sortie se
trouvant sur la plaque de support, et le générateur d'électrons positionné dans la
chambre à vide étant positionné à l'intérieur de la partie de paroi annulaire en céramique
continue du récipient sous vide.
11. Procédé selon la revendication 10, comprenant de plus l'étape consistant à munir d'ondulations
l'élément en céramique allongé.
12. Procédé selon la revendication 11, comprenant de plus l'étape de fixation d'un élément
de ressort annulaire (108) à la membrane à fenêtre de sortie et à l'élément en céramique
et entre ceux-ci.
13. Procédé selon la revendication 10, comprenant de plus l'étape consistant à entourer
l'élément en céramique par une enveloppe métallique (122).
14. Procédé selon la revendication 13, dans lequel l'élément en céramique comprend un
trou tronconique (126a), le procédé comprenant de plus les étapes consistant à :
étendre un conducteur électrique (128) à travers le trou tronconique afin de délivrer
une alimentation au générateur d'électrons ;
entourer le conducteur électrique avec un bouchon isolant souple (126), le bouchon
comprenant une surface tronconique pour réaliser une étanchéité avec le trou tronconique
; et
maintenir le bouchon à l'intérieur du trou tronconique avec un capuchon de maintien
(140) fixé à l'enveloppe.
15. Procédé selon la revendication 10, dans lequel la plaque de support comporte à travers
celle-ci une série de trous afin de permettre aux électrons de la traverser, la configuration
des trous pouvant être agencée de façon à sélectionner une perméabilité aux électrons
à travers la plaque de support afin de communiquer au faisceau d'électrons un profil
d'intensité variable.
16. Procédé selon la revendication 10, dans lequel la membrane à fenêtre de sortie est
formée par une feuille de titane ayant une épaisseur inférieure à 12,5 micromètres.