Source: http://www.google.com/patents/US5121031?ie=ISO-8859-1
Timestamp: 2015-07-06 03:22:52
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Matched Legal Cases: ['art 10', 'art 11', 'art 11', 'art 10', 'art 10', 'art 6']

Patent US5121031 - Microwave electron gun - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA microwave electron gun for a linear accelerator uses microwave energy to impart an initial acceleration to electrons emitted from a lanthanum-hexaboride cathode. The microwaves are contained in an electron-gun cavity, the upstream wall of which has a protruding part surrounding the entrance opening...http://www.google.com/patents/US5121031?utm_source=gb-gplus-sharePatent US5121031 - Microwave electron gunAdvanced Patent SearchPublication numberUS5121031 APublication typeGrantApplication numberUS 07/690,569Publication dateJun 9, 1992Filing dateApr 24, 1991Priority dateAug 4, 1988Fee statusPaidAlso published asUS5029259, US5132593Publication number07690569, 690569, US 5121031 A, US 5121031A, US-A-5121031, US5121031 A, US5121031AInventorsSusumu NishiharaOriginal AssigneeMitsubishi Denki Kabushiki KaishaExport CitationBiBTeX, EndNote, RefManPatent Citations (5), Referenced by (1), Classifications (9), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetMicrowave electron gun
US 5121031 AAbstract
A microwave electron gun for a linear accelerator uses microwave energy to impart an initial acceleration to electrons emitted from a lanthanum-hexaboride cathode. The microwaves are contained in an electron-gun cavity, the upstream wall of which has a protruding part surrounding the entrance opening that accommodates the cathode, and the downstream wall of which has a flat part surrounding an exit opening. The rest of the downstream wall has a radius of curvature equal to that of the other microwave cavities in the accelerating tube, and its center of curvature is aligned with theirs. The cathode is fused to a pair of carbon electrodes to form a cathode block, which is held by clamping between a pair of electrode bars, thus forming a cathode tube. The cathode tube is inserted into a sleeve upstream of the entrance opening in the electron-gun cavity, and is surrounded at a distance of one quarter-wavelength from the cathode by a disk-shaped choke cavity extending one quarter-wavelength from the cathode tube. This electron gun is easy design and operate, and prevents loss of microwave energy.
1. A microwave electron gun for generating an electron beam to be accelerated by a microwave electric field in an accelerating tube having a series of cavities, comprising:an electron-gun cavity for initially accelerating an electron beam, said electron-gun cavity being the first of the series of cavities in the accelerating tube, an upstream wall of which comprises a protruding part surrounding an entrance opening and a downstream wall of which comprises a flat part surrounding an exit opening for forming a converging microwave electric field therebetween; and a cathode, disposed in the entrance opening of said electron-gun cavity, for emitting the electron beam into said electron-gun cavity, microwave radiation being transmitted into said electron-gun cavity from a downstream one of said series of cavities to generate said converging microwave electric field which confines and directs the electron beam from the entrance opening to the exit opening. 2. The microwave electron gun according to claim 1, wherein the portion of the downstream wall of said electron-gun cavity other than said flat part has a radius of curvature equal to a radius of curvature of walls of the other of the series of cavities of the accelerating tube.
3. The microwave electron gun according to claim 2, wherein a center of curvature of said portion of the downstream wall of said electron-gun cavity other than said flat part is aligned with a center of curvature of the other of the series of cavities of the accelerating tube.
4. The microwave electron gun of claim 1, wherein said protruding part has a diameter which is greater than a diameter of the exit opening.
5. A microwave electron gun for generating an electron beam to be accelerated by interaction with accelerating microwave radiation in a series of accelerating cavities in an accelerating tube, comprising:an electron gun cavity, for imparting initial acceleration to the electron beam, disposed at a first end of the accelerating tube, said electron gun cavity having a downstream wall with a flat portion surrounding an exit opening leading to the other of the series of the accelerating cavities and an upstream wall with a protruding portion surrounding an entrance opening disposed opposite said exit opening; sleeve means disposed within said entrance opening and extending outward away from said electron gun cavity; cathode tube means, disposed within said sleeve means and separated from an inner sleeve wall of said sleeve means by a gap; a cathode, mounted within said cathode tube means near said entrance opening, for emitting the electron beam into said electron gun cavity; and microwave generating means, coupled to downstream one of the series of accelerating cavities, for transmitting microwave radiation into said electron gun cavity to form a converging microwave electric field between said protruding portion and said flat portion to confine and direct the electron beam from the entrance opening to the exit opening. 6. The microwave electron gun of claim 5, wherein the downstream wall of said electron-gun cavity other than said flat portion has a radius of curvature equal to a radius of curvature of walls of the other of the series of accelerating cavities of the accelerating tube.
7. The microwave electron gun of claim 6, wherein a center of curvature of the downstream wall of said electron-gun cavity other than said flat portion is aligned with a center of curvature of the other of the series of cavities of the accelerating tube.
8. The microwave electron gun of claim 5, further comprising a side cavity, connected between peripheral portions of said electron gun cavity and a first of a downstream one of the series of accelerating cavities through coupling openings, for coupling the microwave radiation from said microwave generating means into said electron gun cavity.
9. The microwave electron gun of claim 8, said side cavity being a vertical, disk-shaped hollow with bolt means mounted thereon for changing a volume of said side cavity.
10. The microwave electron gun of claim 5, wherein said protruding portion has a diameter which is greater than a diameter of the exit opening.
11. A method of generating an electron beam in a microwave electron gun having a series of accelerating cavities disposed after an electron gun cavity, comprising the steps of:forming a flat portion of the electron gun cavity to surround an exit opening of a downstream wall of the electron gun cavity, the exit opening leading to the series of accelerating cavities; forming a protruding portion of the electron gun cavity to surround an entrance opening of an upstream wall of the electron gun cavity; generating and transmitting an electron beam into the electron gun cavity, using a cathode mounted within cathode tube means inside the entrance opening; and generating and transmitting microwave radiation into the electron gun cavity through a first of the series of accelerating cavities, using a microwave generating means, to form a converging microwave electric field between the protruding portion and the flat portion to confine and direct the electron beam from the entrance opening to the exit opening. Description
This application is a divisional of copending application Ser. No. 07/385,149, filed on Jul. 26, 1989. The entire contents of which are hereby incorporated by reference.
A microwave electron gun according to an embodiment of this invention provides an electron beam that is accelerated by a microwave electric field in an accelerating tube having a series of cavities, and comprises an electron-gun cavity, the upstream wall of which has a protruding part surrounding an entrance opening and the downstream wall of which has a flat part surrounding an exit opening. The rest of the downstream wall has a radius of curvature equal to that of the other microwave cavities in the accelerating tube, and its center of curvature is aligned with theirs. Extending upstream from the entrance opening is a sleeve in which a cathode tube is inserted. The cathode tube comprises a pair of electrode bars, at one end of which a cathode block is held by clamping. The cathode block comprises a lanthanum-hexaboride cathode, to which is fused to a pair of carbon electrodes that contact the electrode bars. The sleeve is surrounded at a distance of one quarter-wavelength from the cathode by a disk-shaped choke cavity extending one quarter-wavelength from the cathode tube.
FIG. 1 is a sectional drawing illustrating a choke cavity structure of an embodiment of the present invention;
FIG. 2 is a sectional drawing illustrating a structure of the electron-gun cavity of an embodiment of the invention;
FIG. 3 is a sectional drawing illustrating a structure of the cathode tube of an embodiment of the invention;
FIG. 4 is an end-on drawing showing an example of the clamping of the cathode block in the cathode tube; and
FIG. 5 is an end-on drawing showing another example of clamping of the cathode block in the cathode tube.
FIG. 1 is a sectional view illustrating the overall structure of a novel microwave electron gun showing a first aspect of the invention. The novel microwave electron gun comprises an electron-gun cavity 1, the detailed structure and function of which will be explained in the description of the second aspect of the invention, and a cathode tube 2, the detailed structure and function of which will be explained in the description of the third aspect of the invention. The electron-gun cavity 1 and cathode tube 2 are disposed near the upstream end of an accelerating tube 3. The electron-gun cavity 1 has an exit opening 1b on its downstream side, for the passage of an electron beam 5 into downstream cavities in the accelerating tube 3, and an entrance opening 1a on its upstream side, which opens into a sleeve 4 of the accelerating tube 3. The cathode tube 2 is disposed in the sleeve 4, with a slight gap between the cathode tube 2 and the wall of the sleeve 4. The function of the cathode tube is to support a cathode 6 for the emission of electrons. The cathode 6 is disposed at the end of the cathode tube 2 near the entrance opening 1a in the electron-gun cavity 1, facing toward the exit opening 1b.
The choking mechanism is well known, being employed in the choke couplings of microwave waveguides, for example, and can be described as follows. The gap between the cathode tube 2 and the sleeve 4 forms a waveguide with an electrical length of one quarter-wavelength, at the end of which choke cavity 7 forms a quarter-wavelength circuit that is shorted at its far end. From the entrance opening 1a in the electron-gun cavity 1, therefore, the microwaves that enter the gap between the cathode tube 2 and the sleeve 4 appear to enter directly into a short circuit with an electrical length of one-half wavelength. This is equivalent to a barrier at the location of the entrance opening 1a, choking off the escape of microwave energy. The effectiveness of the choking action is enhanced by the small size of the gap between the cathode tube 2 and the sleeve 4, resulting in low impedance, and the much greater size of the choking cavity 7, resulting in high impedance.
FIG. 2 illustrates a second aspect of the novel microwave electron gun, showing a more detailed structure of the electron-gun cavity 1.
When the phase of the microwave electric field 15 is from 0� to 180�, the field points from the protruding part 10 toward the flat part 11a and the acceleration is positive. When the phase of the microwave electric field 15 is from 180� to 360�, however, the field points from the flat part 11a toward the protruding part 10 and the acceleration is negative, causing the electron beam 5 first to decelerate, then to accelerate back toward the cathode 6. Alternatively, the decelerating field may prevent the electrons from leaving the cathode 6 at all.
Electrons emitted from the cathode 6 near the peak accelerating phase of the microwave electric field 15 gain enough energy to cross the electron-gun cavity 1 to the exit opening 1b, from which they pass into the accelerating cavity 8 and are accelerated to successively higher energies in the downstream cavities. Electrons emitted in other phases either fail to leave the cathode 6, or lose their energy before reaching the exit opening 1b and are accelerated back toward the cathode 6 in the decelerating phase.
The microwave electric field 15 formed in the electron-gun cavity 1 is a converging field that confines the electron beam 5 and directs it toward the exit opening 1b. In order to create a converging field, the protruding part 10 must be larger in diameter than the exit opening 1b in the partition 11.
FIG. 3 is a sectional drawing illustrating a third aspect of a invention, showing the detailed structure of the cathode tube 2 and the cathode 6. The cathode 6 is made of lanthanum hexaboride (LaB6), and is enlarged at the electron-emitting end 6a. The rear part 6b of the cathode 6 behind the electron-emitting end 6a is fused to a pair of carbon electrodes 16 which also serve as a cathode heater. The cathode 6 and the carbon electrodes 16 form an integral structure referred to as a cathode block 17. The cathode block 17 is held clamped between a pair of semi-cylindrical electrode bars 18, clamping force being maintained by a bolt 19 that is inserted through one electrode bar 18 and screwed into the other. To prevent current from flowing through the bolt 19, the head end of the bolt 19 is insulated from the electrode bar 18 through which it passes by an insulating collar 20. In addition, a plurality of insulating bearings 21 are disposed in depressions in the electrode bars 18 at positions near the bolt 19. The insulating bearings 21 are substantially spherical in shape and can be made of, for example, a ceramic material.
During operation, a voltage is applied across the two terminal bolts 23, causing a flow of current through the electrode bars 18 and the carbon electrodes 16. The bolt 19, by applying pressure to the electrode bars 18 through the insulating collar 20, improves the electrical contact between the electrode bars 18 and the carbon electrodes 16. The current flow heats the carbon electrodes 16, which in turn heat the cathode 6 and cause a thermionic emission of electrons.
The novel electron gun structure illustrated in FIG. 3 enables the cathode 6 to be positioned close to the entrance opening 1a of the electron-gun cavity 1, so that the electrons emitted by the cathode 6 can be accelerated directly by microwave radiation in the cavity. The advantage is that no dc voltage is required to impart an initial acceleration to the electrons. The structure illustrated in FIG. 3 also enables the cathode tube of the electron gun to be easily mounted and accurately positioned.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS3558967 *Jun 16, 1969Jan 26, 1971Varian AssociatesLinear beam tube with plural cathode beamlets providing a convergent electron streamUS4286192 *Oct 12, 1979Aug 25, 1981Varian Associates, Inc.Variable energy standing wave linear accelerator structureUS4629938 *Mar 29, 1985Dec 16, 1986Varian Associates, Inc.Standing wave linear accelerator having non-resonant side cavityUS4746839 *Jun 16, 1986May 24, 1988Nec CorporationSide-coupled standing-wave linear acceleratorUS4988919 *Feb 8, 1988Jan 29, 1991Varian Associates, Inc.Small-diameter standing-wave linear accelerator structure* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS5986415 *Jan 30, 1998Nov 16, 1999Mitsubishi Denki Kabushiki KaishaLinear electron accelerator* Cited by examinerClassifications U.S. Classification315/5.41, 315/505, 315/5.39International ClassificationH05H9/04, H01J23/04Cooperative ClassificationH05H9/04, H01J23/04European ClassificationH05H9/04, H01J23/04Legal EventsDateCodeEventDescriptionNov 27, 1995FPAYFee paymentYear of fee payment: 4Nov 30, 1999FPAYFee paymentYear of fee payment: 8Nov 12, 2003FPAYFee paymentYear of fee payment: 12RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services