US3924152A - Electron beam amplifier tube with mismatched circuit sever - Google Patents

Electron beam amplifier tube with mismatched circuit sever Download PDF

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Publication number
US3924152A
US3924152A US520524A US52052474A US3924152A US 3924152 A US3924152 A US 3924152A US 520524 A US520524 A US 520524A US 52052474 A US52052474 A US 52052474A US 3924152 A US3924152 A US 3924152A
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Prior art keywords
wave
circuit
slow
elements
energy
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US520524A
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English (en)
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Robert J Butwell
Gordon T Hunter
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Varian Medical Systems Inc
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Varian Associates Inc
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Priority to US520524A priority Critical patent/US3924152A/en
Priority to GB4461275A priority patent/GB1469199A/en
Priority to FR7533712A priority patent/FR2290028A1/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/16—Circuit elements, having distributed capacitance and inductance, structurally associated with the tube and interacting with the discharge
    • H01J23/24—Slow-wave structures, e.g. delay systems
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/61—Hybrid tubes, i.e. tubes comprising a klystron section and a travelling-wave section

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  • ABSTRACT An electron beam amplifier tube has a traveling wave output circuit. electrically isolated from the signal input circuit so that the output circuit is excited only by beam electron current.
  • the upstream end of the output circuit' is terminated with an impedance which reflects a substantial part of the backward wave energy flowing toward the upstream end.
  • the phase and amplitude of the reflection may be chosen to reinforce the beam-circuit interaction, thereby improving tube efficiency.
  • the invention relates to microwave amplifier tubes wherein a beam of electrons interacts with an electromagnetic wave on a slow-wave circuit which wave travels with velocity approximately equal to that of the electron beam.
  • Such tubes include crossed field amplifiers, linear beam traveling wave tubes and hybrid traveling wave tubes with klystron-like driver sections known by the registered trademark Twystron". These types of tubes provide amplification over a wide frequency range and can be designed for high power output and high efficiency.
  • the gain increases with the length of the slow-wave interaction circuit.
  • the gain becomes too high, e.g., db or more, instabilities arise due to reflection of wave energy from the inevitable small transmission line impedance mismatches at the ends of the circuit. The reflected energy is reamplified, producing instability.
  • the matched termination customarily provided at the upstream end of a downstream severed section was intended to prevent reflection of any wave traveling backward upstream in that section, because amplification of the wave reflected downstream creates regeneration.
  • the principal object of the present invention is to provide a wide-band, electron beam, microwave ampli bomb tube with improved efficiency.
  • Another object is to provide a tube whose performance is insensitive to wave reflections from its load.
  • Another object is to provide a tube of simplified construction.
  • thepresent invention has produced increased efficiency with a short, low gain circuit. Since the gain of the output circuit is low, changes in output load match produce smaller perturbations of the tube performance. Also, the short traveling wave circuit is simpler to fabricate and cheaper than previous long, high gain circuits.
  • FIG. 1 is a schematic elevation view, partly in section, of a hybrid linear beam amplifier embodiment of the invention.
  • FIG. 2 is an enlarged section of the output circuit of the amplifier of FIG. 1.
  • FIG. 3A is an enlarged plan view section of the circuit of FIG. 2 along the line 3A3A.
  • FIG. 3B is an isometric view of a cavity of an alternative slow-wave circuit.
  • FIG. 4 is an elevation section of a portion of another embodiment of the invention corresponding to section 4 of FIG. 3A.
  • FIG. 5 is a view similar to FIG. 4 of still another embodiment.
  • FIG. 6 is a view similar to FIG. 4 of still another embodiment.
  • FIG. 7 is a schematic section of a crossed-field amplifier embodying the invention.
  • the present invention is applicable to any electron beam amplifier tube wherein radio frequency power is extracted from the beam by interaction with an electromagnetic wave traveling at approximately the beam velocity on a severed circuit.
  • Such tubes include linear beam traveling wave tubes and hybrid Twystron ampli bombs as well as crossed-field amplifiers with injected beam.
  • Twystron hybrid embodiment will be described in detail.
  • FIG. 1 illustrates a hybrid Twystron amplifier.
  • a cylindrical electron beam is formed by an axially symmetric gun comprising a concave thermionic cathode 11, as of porous tungsten impregnated with barium aluminate, and surrounded by a beam-focusing electrode 12 as of austenitic stainless steel operated at the same potential as cathode l 1.
  • Gun 10 is mounted on a metallic base (not shown) sealed to a ceramic insulating cylinder 21, as by brazing. The other end of cylinder 21 is brazed to a steel cup 22 surrounding gun 10.
  • a central aperture in cup 22 is brazed to a copper anode electrode 23 containing a central axial aperture 24.
  • a negative voltage applied to gun 10 with respect to anode 23 draws a converging electron beam through aperture 24.
  • an iron polepiece 25 Surrounding anode 24 is an iron polepiece 25 for directing the field of a surrounding solenoid magnet (not shown) axially of the beam to focus it in an extended cylindrical outline.
  • the beam passes through a series of kylstron-type cavities 30, 31, as of copper, provided with reentrant annular drift tube sections 32 defining beam interaction gaps 33.
  • the first, upstream cavity is coupled via a conductive loop 34 to a coaxial transmission line 35 carrying the input drive signal for the amplifier.
  • the signal is amplified by the well-known klystron velocity modulation process.'The resonant frequencies and Us of cavities 30, 31 are staggered as taught by the aforecited US. Pat. No. 3,289,032 to provide a tightly bunched beam overa wide frequency range such as 10% of the center frequency.
  • the bunched beam enters a traveling wave output circuit 40 comprising a series of cavities 41 (FIG. 2) as of the cloverleaf type described in U.S. Pat. No. 3,233,139 issued Feb. 1, 1966 to Marvin Chodorow and assigned to the present assignee.
  • the cavities are mutually coupled by radial slots 42 (FIG. 3A) to form a bandpass circuit propagating a forward-fundamental slow wave for interaction with the electron beam in the well-known traveling wave tube fashion.
  • Toward the output end of the circuit the axial heights of the cavities are tapered to smaller values to reduce the circuit wave velocity to match the reducing velocity of the electrons as kinetic energy is extracted from them.
  • the tapering principle is described in U.S. Pat. No. 3,374,390 issued Mar. 19, 1968 to J. A. Ruetz, W. H. Yocom and Rene M. Rogers and assigned to the present assignee.
  • the final cavity 43 is coupled through an iris aperture 44 to a reduced height rectangular output waveguide 45 which is matched by a tapering height section 46 to a standard height output waveguide 47. interposed between two sections of guide 47 is a short section of cylindrical guide 48 sealed by a ceramic vacuum window 49 as described in U.S. Pat. No. 2,958,834, issued Nov. 1, 1960 to R. S. Symons and A. E. Schoennauer and assigned to the present assignee.
  • the beam After passing through traveling wave output circuit 40 the beam goes through a second magnetic polepiece 50 which terminates the axial focusing field. The beam then expands and is collected on the inner surface 51 of a collector 52, as of copper, mounted on polepiece 50 via a cylindrical ceramic insulator 53. Collector 52 is cooled by water circulating through inlet and outlet pipes 54 and small enclosed channels (not shown) in the copper collector walls.
  • the electron beam enters output traveling wave circuit 40 with the electrons gathered into periodic bunches by the velocity modulation in the klystron section.
  • the alternating space current component represented by the bunches induces rf circulating current in the circuit cavities. This in turn produces an rf voltage wave traveling with the beam which increases the bunching, so the signal is amplified.
  • energy is transferred from the beams kinetic energy to the circuit wave which is carried to the useful output.
  • the electromagnetic fields in any given cavity couple energy through the coupling slots to its two adjacent cavities, upstream and downstream, in approximately equal amounts.
  • the downstream fields add in proper phase to those generated in succeeding downstream cavities to produce the growing forward traveling wave.
  • the upstream fields of the successive circuit periods add up in a cancelling phase, so there is very little backward flow of power.
  • the gain per cavity may be as much as 3 db. In this case the cancellation of backward waves is very imperfect.
  • the backward wave power may sometimes even exceed the forward wave and may be a sizeable fraction of the tubes output power.
  • the upstream cavity of traveling wave circuit 40 is coupled via an iris aperture 61 to a waveguide 62 which tapers from the height of cavity 60 to a standard height.
  • circuit 40 is matched for backward traveling waves into guide 62.
  • the desired wave reflection is caused by an impedance transformer 63 in guide 62. Any standard impedance transformer may be used. Transformer 63 is a capactive iris for example.
  • the amplitude of the reflection is controlled by the height of the iris and the phase by its distance from cavity 60. More complex microwave transformers may be used to adjust the phase and amplitude of the reflection to be a desired function of frequency as is well-known in the art of microwave impedance matching.
  • Wave power not reflected by transformer 63 proceeds down guide 62 and is absorbed by a matched load termination 64, for example, a block of ceramic loaded with carbon particles and tapered in height to provide a broadband match.
  • a matched load termination 64 for example, a block of ceramic loaded with carbon particles and tapered in height to provide a broadband match.
  • FIG. 3A illustrates a Cloverleaf cavity, as indicated in FIG. 2, with the upper lid removed to show coupling slots 42.
  • FIG. 3A also shows the coupling of upstream cavity 41 to sever load waveguide 62 through iris aperture 61.
  • the width of iris 61 is adjiisted to provide the correct coupling to match the impedance of slow-wave circuit 40 to waveguide 62.
  • FIG. 3B shows an alternate cavity useful as an element of a traveling wave circuitaccording to the present invention.
  • the cavity 41 is a simple cylinder with short drift tubes 70 projecting from each end wall 71. Coupling to adjacent cavities is through iris slots 72.
  • the fundamental traveling wave is a backward wave, but drift tubes 70 introduce space harmonic fields with a forward component which can interact with the beam.
  • FIG. 4 shows a different embodiment of the invention as applied to the same type of slow-wave circuit 40 as shown in FIGS. 1 and 2.
  • waveguide 62 is ter minated in a short circuit 65 at a distance from cavity coupling iris 61 selected to reflect backward wave energy into cavity 60 in the proper phase.
  • the amplitude of the reflected wave is controlled by a button of lossy dielectric material 66, as of carbon grains dispersed in beryllium oxide ceramic, disposed within cavity 60 to absorb some of the energy therein. In some embodiments a complete reflection may be desired and lossy button 66 would then be omitted.
  • FIG. 5 illustrates another embodiment using a slowwave circuit 40 similar to the circuit of FIGS. 1 and 2.
  • the phase of the reflected wave is controlled by the resonant frequency of the first cavity 60.
  • the resonant frequency of cavity 60' is set so that energy is reflected in the desired phase.
  • the amplitude of the reflection is determined by the size of iris 61 which determines the amount of backward wave energy coupled into waveguide 62 and absorbed in load 64.
  • the backward wave is not matched to the load waveguide but partially reflected at iris 61'.
  • FIG. 6 shows still another embodiment wherein both phase and amplitude of the backward wave are controlled internally of first cavity 60.
  • the resonant frequency determined by nose spacing d, determines the phase.
  • the cavity Q. determined by lossy button 66 determines the amplitude.
  • button 66 may be omitted to produce complete reflection.
  • FIG. 7 shows a highly schematic embodiment of the invention in an injected-beam crossed field amplifier.
  • a thermionic cathode 72 heated by a radiant heater 73.
  • a beam of electrons 71 is drawn from cathode 72 by an accelerating anode 74 at a positive potential 86 with respect to cathode 72.
  • a uniform magnetic field B perpendicular to the cathode and anode surfaces directs the beam perpendicularly to its initial direction and away from the cathode.
  • circuit 76, 77 is structurally integral with vacuum envelope 70, the metallic parts of which are operated at the dc potential of circuit 76, 77.
  • Electron beam 71 drifts lengthwise of sole electrode and circuit 76, 77 under the influence of the crossed electric and magnetic fields.
  • the field amplitudes are selected so that the average drift velocity approximates thewave velocity on circuit 76, 77.
  • Circuit 76, 77 is severed into two parts 76 and 77 which are isolated against wave energy transmission therebetween by anon-propagating sever section 78.
  • the input circuitsection 76 is: matched at its upstream end to a waveguide 79 for introducing the input microwave signal.
  • the signal is amplified by synchronous interaction with beam 71
  • circuit 76 is matched to a load waveguide 80 terminated in a non-reflective load 81.
  • the rf signal is carried over to output circuit 77 by the ac component of current on beam 71.
  • the upstream end of circuit 77 is coupled to a waveguide 82 provided with a wave-reflecting transformer 83 and a matched load 84 to absorb non-reflected energy.
  • Backward wave energy on circuit 77 is reflected in guide 82 with a phase and amplitude selected to enhance the interaction of the combined forward wave and the electron beam.
  • the forward wave is amplified in output circuit section 77 and matched at the downstream end thereof into output waveguide 85 for conduction to a useful load.
  • An electron beam amplifier tube comprising; a vacuum envelope, means for forming and directing a beam of electrons, means for collecting said electrons, first circuit means for modulating said beam at a high frequency, second circuit means downstream of said first circuit means and isolated therefrom to prevent propagation of electromagnetic energy therebetween, said second circuit means comprising, a slow-wave circuit capable of propagating a traveling wave in energyexchanging relationship with said beam and having an upstream end adjacent said first circuit means and a downstream end removed from said upstream end in the direction of flow of said electrons,
  • said terminating means comprises means for reflecting into a downstream flowing wave a selected substantial portion of wave energy flowing upstream in said slow wave circuit toward said upstream end, the reflected wave having a phase with respect to said upstream wave selected to increase the effi' ciency of said tube over a wide operational frequency range.
  • said reflecting means comprises means for reflecting substantially all of said wave energy flowing in said slow-wave circuit.
  • said reflecting means comprises a transmission line coupled to said upstream end of said slow-wave circuit and containing a wavereflective impedance discontinuity.
  • said reflecting means comprises one of said periodic elements with electrical characteristics different from succeeding said elements comprises energy-attenuating means.

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US520524A 1974-11-04 1974-11-04 Electron beam amplifier tube with mismatched circuit sever Expired - Lifetime US3924152A (en)

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Application Number Priority Date Filing Date Title
US520524A US3924152A (en) 1974-11-04 1974-11-04 Electron beam amplifier tube with mismatched circuit sever
GB4461275A GB1469199A (en) 1974-11-04 1975-10-29 Electron beam amplifier tube with mismatched circuit sever
FR7533712A FR2290028A1 (fr) 1974-11-04 1975-11-04 Tube amplificateur a faisceau d'electrons avec un circuit sectionne desadapte

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4019087A (en) * 1975-03-20 1977-04-19 Nippon Electric Company, Ltd. Coupled-cavity type traveling-wave tube with sever termination attenuators
US4147956A (en) * 1976-03-16 1979-04-03 Nippon Electric Co., Ltd. Wide-band coupled-cavity type traveling-wave tube

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3123736A (en) * 1964-03-03 Severed traveling-wave tube with external terminations
US3365607A (en) * 1963-09-20 1968-01-23 Varian Associates Electron discharge device
US3538377A (en) * 1968-04-22 1970-11-03 Varian Associates Traveling wave amplifier having an upstream wave reflective gain control element
US3576460A (en) * 1968-08-08 1971-04-27 Varian Associates Impedance match for periodic microwave circuits and tubes using same
US3594605A (en) * 1969-10-31 1971-07-20 Varian Associates Mode suppression means for a clover-leaf slow wave circuit
US3668544A (en) * 1970-09-03 1972-06-06 Varian Associates High efficiency traveling wave tube employing harmonic bunching
US3852635A (en) * 1972-07-31 1974-12-03 Siemens Ag Transit-time amplifier tube with stabilized delay

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3123736A (en) * 1964-03-03 Severed traveling-wave tube with external terminations
US3365607A (en) * 1963-09-20 1968-01-23 Varian Associates Electron discharge device
US3538377A (en) * 1968-04-22 1970-11-03 Varian Associates Traveling wave amplifier having an upstream wave reflective gain control element
US3576460A (en) * 1968-08-08 1971-04-27 Varian Associates Impedance match for periodic microwave circuits and tubes using same
US3594605A (en) * 1969-10-31 1971-07-20 Varian Associates Mode suppression means for a clover-leaf slow wave circuit
US3668544A (en) * 1970-09-03 1972-06-06 Varian Associates High efficiency traveling wave tube employing harmonic bunching
US3852635A (en) * 1972-07-31 1974-12-03 Siemens Ag Transit-time amplifier tube with stabilized delay

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4019087A (en) * 1975-03-20 1977-04-19 Nippon Electric Company, Ltd. Coupled-cavity type traveling-wave tube with sever termination attenuators
US4147956A (en) * 1976-03-16 1979-04-03 Nippon Electric Co., Ltd. Wide-band coupled-cavity type traveling-wave tube

Also Published As

Publication number Publication date
FR2290028A1 (fr) 1976-05-28
GB1469199A (en) 1977-03-30
FR2290028B3 (enExample) 1978-05-12

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