CA1175144A - Collector-output for hollow beam electron tubes - Google Patents

Collector-output for hollow beam electron tubes

Info

Publication number
CA1175144A
CA1175144A CA000398576A CA398576A CA1175144A CA 1175144 A CA1175144 A CA 1175144A CA 000398576 A CA000398576 A CA 000398576A CA 398576 A CA398576 A CA 398576A CA 1175144 A CA1175144 A CA 1175144A
Authority
CA
Canada
Prior art keywords
waveguide
collector
tube
wave
gap
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000398576A
Other languages
French (fr)
Inventor
Norman J. Taylor
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Varian Medical Systems Inc
Original Assignee
Varian Associates Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Varian Associates Inc filed Critical Varian Associates Inc
Application granted granted Critical
Publication of CA1175144A publication Critical patent/CA1175144A/en
Expired legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/36Coupling devices having distributed capacitance and inductance, structurally associated with the tube, for introducing or removing wave energy
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/02Electrodes; Magnetic control means; Screens
    • H01J23/027Collectors

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  • Microwave Tubes (AREA)

Abstract

Abstract Collector-Output for Hollow Beam Electron Tubes In a microwave electron tube such as a gyrotron, a hollow beam of electrons passes thru the inter-action cavity into an output waveguide carrying the generated energy in a mode with circular electric fields. According to the invention, the beam is caused to expand, passing thru a gap in the wave-guide to be collected on a larger, surrounding col-lector. The collector energy is thus reduced. The wave energy jumps the gap and continues down the waveguide. Wave energy leaking into the collector may be absorbed by lossy material therein or be carried off by waveguides to external loads.

Description

- 1175~4 Collector-Out ut for Hollow Beam Electron Tubes P

Field of the Invention The invention pertains to electron tubes for generating very high power at very high frequency.
The gyrotron is a modern example. Such tubes typi-cally use wave propagating circuits operating in a higher-order mode such as a mode with circular electric field.

Prior Art Gyrotron tubes have generally been built with a beam-interac-tion cavity designed for supporting an electromagnetic wave in a TE mode. Accidental oml cOnversion of this mode to other modes which can also be supported in the cavity is a problem.
- Conversion to non-circular-field modes is caused by any departure of the circuits from circular symmetry. Thus, it has been common practice to make the output waveguide cylindrical, coaxial with the interaction cavity, and adapted to propagate the TEom mode. The hollow electron beam is expanded by terminating the axial magnetic focusing ~!

1~51~4 field. The beam is -then collected on the surrounding waveguide wall, while the wave continues on through a dielectric output window.
A principal disadvantage of the prior art arrangement is that the size, and thus the power-dissipating ability of the collector,is limited by the waveguide diameter.
This may also be aided by increasing the dia-meter of the waveguide. If this :is then subsequently reduced in *iameter prior to the output window, for example, some of the higher order modes created at the taper discontinuities may be trapped and resonate.
If sufficient loss is not provided in the expanded sectionr the amplitudes may build to such a level that the operation of the tube is disrupted through reflection to the cavity in modes capable of trans-mission to it. This results in erratic output and often frequency skipping to competing modes.
In the design of some gyrotrons it is found t~at the magnetic field can no longer control the beam along the length of an extended collector. It is then necessary to further increase the diameter of the collector to provide sufficient area from beam dissipation. This means either increased discon-tinuities or excessively long tapers.

Summary of the Invention An object of the invention is to provide a gyrotron tube with increased power.
A further object is to provide a gyrotron tube ~ith reduced spurious oscillations.
These objects are achieved by a transverse gap in the output waveguide thru which the spent electron beam is directed from the guide outward into a larger, surrounding cavity on whose walls ~i 1 ~75 14~
--3--it is collected. Wave energy leaking into the collector cavity is abscrbed by a load which may be inside the collector vacuum envelope or external to it.

Brief Description of the Drawings FIG. 1 is a schematic axial section of a prior art gyrotron oscillator.
FIG. 2 is a schematic axial section of the output section of a modified prior art gyrotron.
FIG. 3 is a schematic axial section of the out-put section of a gyrotron embodying the invention.
FIG. 4 is a schematic axial section of the col-lector section of a modified embodiment.
Description of the Preferred Embodiments FIG. 1 is a sketch of a prior art gyrotron oscillator of the monotron type. The gyrotron is a microwave tube in which a beam of electrons having spiral motions in an axial magnetic field parallel to their drift direction interact with the transverse electric fields of a wave-supporting circuit. The electric field in practical tubes is in a circular-electric field mode. In the gyro-klystron the wave-supporting circuit is a resonant cavity, usually resonating in a TE mode.oml In the gyro-monotron of FIG. 1 a thermionic cathode 20 is supported on the end plate 22 of the vacuum envelope. End plate 22 is sealed to the metallic accelerating anode 24 by a dielectric enve-lope member 26. Anode 24 in turn is sealed to the main tube body 28 by a second dielectric member 30.
In operation, cathode 20 is held at a potential negative to anode 24 by a power supply 32. Cathode 20 is heated by a radiant internal heater. (not shown).

Thermionic electrons are drawn from its conical outer emitting surface by the attractive field of the coaxial conical anode 24. The entire structure is immersed in an axial magnetic field H produced by a surrounding solenoid magnet (not shown). The initial radial motion of the electrons is converted by the crossed electric and magnetic fields to a motion away from cathode 20 and spiralling about magnetic field lines, forming a hollow beam 34. Anode 24 is held at a potential negative to tube body 28 by a second power supply 36, giving further axial accel-eration to the beam 34. In the region between cathode 20 and body 28, the strength of magnetic field H is increased greatly, causing beam 34 to be lS compressed in diameter and also increasing its rota-tional energy at the expense of axial energy. The rotational energy is the part involved in the useful interaction with the circuit wave fields. The axial energy merely provides beam transport through the interacting region.

Beam 34 passes through a drift-tube or aperture 38 into the interaction cavity 40 which is resonant at the operating frequency in a TEoml mode. The magnetic field strength H is adjusted so that the cylotron-frequency rotary motion of the electrons is approximately synchronous with the cavity reson-ance, The electrons can then deliver rotational energy to the circular electric field, setting up a sustained oscillation.
At the output end of cavity d O the inner wall of body 28 may be tapered in diameter to form an iris 42 of size selec'ed to give the proper amount of energy coupling out of cavity 40. In very high power tubes there may be no constricted iris, the cavity being completely open-ended for maximum ~!

- 1~7514a~

coupling. In either case, an outwardly tapered section 44 couples the output energy into a uniform waveguide 46 which has a greater diameter than resonant cavity 40 in order to propagate a traveling wave. Near the output of cavity 40 the magnetic field H is reduced. Beam 34 thus expands in dia-meter under the influence of the expanding magnetic field lines and its own self-repulsive space charge.
Beam 34 is then collected on the inner wall of wave-guide 46, which also serves asa beam collector. Adielectric window 48, as of alumina ceramic, is sealed across waveguide 46 to complete the vacuum envelope.
~ince the beam collector 46 is also the out-put waveguide, its diameter is limited by the pro-pagating dimensions for the operating TEom mode.
Thus, its energy-dissipating capability is also limited. It is found that as TEom gyrotrons are scaled up in frequency the control of the electron beam in the collector becomes weak and therefore it becomes difficult using axisymmetric fields to spread the beam over an extended length of collector.
FIG. 2 is a sketch of the output portion of another prior art gyrotron. Here the cavity 40' is coupled thru a taper section 44' to a collector sec-tion 50 which has a diameter considerably larger than the remainder of the output waveguide 46'. A
second taper 52 slowly reduces the diameter from col-lector 50 to waveguide 46'. The wave passes thru wave-guide 46' thru a dielectric window 48' to the usefulload. The scheme of FIG. 2 reduces the dissipation power density because collector 50 is larger than the waveguide-sized collector of FIG. 1. However, the tapers themselves can cause mode conversionj generally from one mode with circular symmetry to " .

. l 1751 another ~ith the same symmetry. Since the beam collector 50 is also the output waveguide, its dia-meter is limited by the acceptable lengths of taper (U? to it and down to the output guide) required to keep ~ode conversion to a small level. Also, part of the section of enlarged waveguide formed by the collector 50 can support higher order modes for which waveguide 46' is cut off so that these modes cannot escape from the enlarged section. The Q of this section is thus very high and the spurious modes can build up to dangerously large amplitudes. These cause, through conversion to cavity-supported modes and reLlection to the cavity, a disruption of the inter-action, a loss of output and often frequency skipping to a co~.petitive mode. For this reason, loss is normally provided in the expanded diameter collector to limit the amplitude of the trapped resonances.
This may be in the form of a small gap of dimension such that the loss of the desired propagating modes 20 is small, while spurious modes are propagated out and externally absorbed.
FIG. 3 is a section of the output end of a gyrotron tube embodying the invention. The re-sonant cavity 40 " is connected by a tapered sec-tion 44'' to waveguide 46'' which is only slightly larger in diameter than cavity 40'', but large enough to carry a traveling wave. This small taper is less prone to mode convers on than the large taper of prior art FIG. 2.
Waveguide 46'' continues thru window 48 " to the useful load. Waveguide 46'' is interrupted by a gap 56 in the region where beam 34~ t expands. The magnetic field pattern is shap~d so that beam 34'' passes thru gap 56 without hitting waveguide 46 ". Beam 34 "
continues to expand and is collected on the inside l17~

surface 57 of the enlarged collector chamber 58.
Collector surface 57 is cooled by circulating water or other fluid 54''. Inside the ends of collector 58 removed from beam 34'' are inserted rings of wave-absorbing dielectric material 60, such as a beryllia ceramic containing particles of silicon carbide, a very lossy material. Ring 60 may be brazed to the water-cooled wall of collector cavity 58 for conduc-tion cooling, or it may be suspended so it can heat up and radiate the power it absorbs. For additional loss, some inner walls of collector 58 may be coated with a high-resistance metallic coating. These lossy elements absorb any microwave radiation entering collector 58 thru waveguide gap 56, thus preventing the build-up of large amplitude resonances.
The amount of wave energy leaking out of wave-guide 46'' into collector 58 is a decreasing function of the diameterof waveguide 46'' and an increasinq function of the length of gap 56, both measured in free-space wavelengths. Both theorectical calcula-tions and experimental measurements have demonstrated that the energy loss in a practical tube can be made tolerable. For example, measurements on a 5" diameter waveguide show that we could have a gap of 6.5" with a loss of less than 4% at 120GHz in the TEo2 mode of propagation, and we could have a 12" gap with less than 10% loss. These gaps could allow the electron beam to pass to a collector of sufficient diameter to allow proper dissipation.
FIG. 4 is a section of the output end of a gyrotron employing a somewhat different embodiment.
~ere the wave-absorbing function in collector cavity 58''' is performed by sealing one or both ends with a wave-propagating dielectric window 62.
Window 62 is preferably of low-loss material such .~1 .

1 1 7 ;~ 14~

as high-alumina ceramic. Outside windows 62 are water-load sections 64 containing lossy dielectric fluid 66, such as water, circulating thru inlet and outlet pipes 68. The unwanted wave energy is ab-sorbed directly in the body of fluid 66, so the pro-blem of convective heat transfer is greatly reduced.
Alternatively, cavity 58'' may be extended beyond windows 62 as air filled waveguides terminated by any kind of conventional waveguide loads.
In the embodiment of FIG. 4 the output waveguide 46''' may be tapered to a larger diameter 50''' similarly to the scheme of FIG. 3, the difference being that in FIG. 4 the surface 50''' does not have to dissipate the beam energy which is received on the lS even larger surface 57''' of collector cavity 58'''.
The embodiments described above are intended to be illustrative and not limited. Many varia-tions of the invention will become obvious to those skilled in the art. The invention may be applied to any linear-beam tube using an output waveguide carrying a circular electric field mode. At pre-sent, the gyrotron is the most successful of such tubes, but others may be devised. Also, other methods of damping the energy entering the col-lector may be used. The invention is intended tobe limited only by the following claims and their legal equivalents.

~!

Claims (20)

I Claim:
1. In a microwave electron tube:
means for generating a hollow beam of electrons, circuit means for sustaining an electromagnetic wave in interacting relation with said beam, circular waveguide means coaxial with said beam for conducting energy from said wave to an external load in a mode having circular electric fields, a transverse gap in said waveguide for outward passage of said beam, and a hollow electron collector surrounding said gap.
2. The tube of claim 1 further comprising wave absorptive means in wave-transmissive connection with said collector.
3. The tube of claim 1 wherein said collector is a figure of revolution coaxial with said waveguide means.
4. The tube of claim 2 wherein said collector and said wave-absorptive means are figures of revolution coaxial with said waveguide means.
5. The tube of claim 2 wherein said wave absorptive means comprises a layer of resistive material on at least a portion of the inner surface of said collector.
6. The tube of claim 2 wherein said wave absorptive means comprises lossy dielectric material.
7. The tube of claim 6 wherein said dielectric material is inside said collector.
8. The tube of claim 1 further comprising a wave-transmissive dielectric window forming a part of a vacuum envelope of said collector.
9. The tube of claim 8 further comprising means for maintaining lossy dielectric material in wave-transmissive connection with said window.
10. The tube of claim 9 wherein said lossy dielectric material is water.
11. The tube of claim 1 further comprising means for producing a magnetic field coaxial with said beam for directing said beam.
12. The tube of claim 11 further comprising means for reducing the strength of said magnetic field in the vicinity of said gap whereby said beam is directed to pass outwardly through said gap.
13. In a gyrotron type microwave electron tube:
means for generating a hollow beam of electrons;
means for supporting an electromagnetic wave in energy ex-changing interaction with said beam, circular waveguide means of generally uniform cross-sec-tion and coaxial with said beam for conducting energy from said interaction to an external load in a mode having circular electric fields;
said waveguide defining therein a transverse gap for passage of said beam outwardly of said waveguide; and a hollow electron collector coaxial with and outside said waveguide, and surrounding said gap.
14. The tube of claim 13 in which said means for supporting said electromagnetic wave includes a resonant cavity, resonating in a circular electric field mode.
15. The tube of claim 14 in which said cavity has a first dia-meter, and said waveguide means has a second diameter slightly larger than said first diameter.
16. In a gyro device for energy-exchanging interaction between a hollow beam of electrons and an electromagnetic wave:
output waveguide means coaxial with said beam, said means propagating externally of said device and in a circular electric field mode the electromagnetic wave energy resulting from said energy exchanging interaction;
said waveguide means being gapped in the direction of said beam and dividing said waveguide into two discontinuous portions to provide a space permitting said beam to spread outwardly there-through with minimal impingment on said waveguide; and hollow electron collector means surrounding said space and extending about and outside of said waveguide.
17. A gyro device as in claim 16 in which said collector means is substantially larger in diameter than said waveguide means.
18. A gyro device as in claim 16 in which said collector means is extended coaxially along the direction of said beam.
19. In a linear beam microwave electron tube in which a linear electron beam and cm electromagnetic wave undergo energy exchang-ing interaction, the improvement comprising:
output means including a circular waveguide coaxial with said beam for conducting away the energy resulting from said ener-gy exchanging interaction in a mode having circular fields;
a transverse gap within said waveguide for the passage of said beam outwardly of said waveguide; and a hollow electron collector external to said waveguide and surrounding said gap.
20. The tube of claim 19 in which said gap divides said wave-guide into two axially-spaced portions.
CA000398576A 1981-04-06 1982-03-17 Collector-output for hollow beam electron tubes Expired CA1175144A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US25161281A 1981-04-06 1981-04-06
US251,612 1988-09-29

Publications (1)

Publication Number Publication Date
CA1175144A true CA1175144A (en) 1984-09-25

Family

ID=22952693

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000398576A Expired CA1175144A (en) 1981-04-06 1982-03-17 Collector-output for hollow beam electron tubes

Country Status (5)

Country Link
JP (1) JPH0656738B2 (en)
CA (1) CA1175144A (en)
DE (1) DE3211971A1 (en)
FR (1) FR2503451B1 (en)
GB (1) GB2096392B (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2542505B1 (en) * 1983-03-11 1985-10-11 Thomson Csf RESONANT CAVITY FOR MICROWAVE AND RADIO WAVES GENERATOR USING SUCH A CAVITY
FR2542504B1 (en) * 1983-03-11 1986-02-21 Thomson Csf RESONANT CAVITY FOR MICROWAVE, ESPECIALLY FOR ELECTROMAGNETIC ENERGY GENERATORS
FR2543368B1 (en) * 1983-03-25 1985-09-20 Thomson Csf MODES TRANSFORMER
JP2892151B2 (en) * 1990-11-27 1999-05-17 日本原子力研究所 Gyrotron device
FR2688342B1 (en) * 1992-03-06 2001-10-05 Thomson Tubes Electroniques ELECTRONIC MICROWAVE TUBE.
FR2756970B1 (en) * 1996-12-10 2003-03-07 Thomson Tubes Electroniques LONGITUDINAL INTERACTION MICROWAVE TUBE WITH OUTPUT BEYOND THE COLLECTOR

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5838904B2 (en) * 1974-04-20 1983-08-26 日本電気株式会社 Microhakan
US4200820A (en) * 1978-06-30 1980-04-29 Varian Associates, Inc. High power electron beam gyro device
US4189660A (en) * 1978-11-16 1980-02-19 The United States Of America As Represented By The United States Department Of Energy Electron beam collector for a microwave power tube
EP0058039B1 (en) * 1981-02-10 1985-02-20 Thorn Emi-Varian Limited Gyrotron device
US4388555A (en) * 1981-03-09 1983-06-14 Varian Associates, Inc. Gyrotron with improved stability

Also Published As

Publication number Publication date
DE3211971C2 (en) 1990-12-20
JPS57165938A (en) 1982-10-13
FR2503451A1 (en) 1982-10-08
GB2096392A (en) 1982-10-13
GB2096392B (en) 1985-04-03
FR2503451B1 (en) 1986-04-04
JPH0656738B2 (en) 1994-07-27
DE3211971A1 (en) 1982-11-04

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