US2892121A - Electron discharge device - Google Patents

Description

LU H W HHM .5u/550e? INVENTOR.

F. L. SALISBURY ELECTRON DISCHARGE DEVICE Filed March 25. 1954 QN l@ S Q June 23, 1959 United States Patent Varian Associates, `Sau Carlos, Calif., a corporation of California Application Marchas, 11954,'sena1 No. v418,714 z claims. (ci. sis- 5.39)

invention 'relatesto electron discharge devices and, more particularly, to anelectrondischarge device of the velocity modulation type arranged to operate at microwave 'frequencies las an amplifier.

As @the operating frequency of electron discharge devices or tubes -has increased, a corresponding increase has been noted with respect to the critical nature of `the alignment `of Athe elements -thereof, the geometric shape and tolerancesof such'elements, and the -losses of `energy resulting from Lanyldeviationin these tube design factors. While vthe design problems presented have been severe with `tubes suchas -reex klystrons and two-cavity klystron amplifiers, they have ibeenfurther accentuated, for obvious reasons, with multi-cavity klystrons, particularly lwhen frequencies of *the -order of 20-30 -`lerne. are approached. In such cases,sincefa wavelength is in the neighborhood of v1 centimeter, even Asuch minor structural :aberrations as produced by 'bracing can laffect -the losses :and the tunability -ofthe amplifier.

Accordingly, a feature of the present invention involves the provision of a multi-cavity microwave amplifier of relatively y'simple lconstruction and lha-ving optimum gain characteristics.

A further feature 'is the provision of a microwave amplifier of .-the `multi-cavity type having a structural farrangement whichfacilitates assembly `andeiilcient operation thereof.

Yet another feature `of lthe yinvention is the provision of a 'microwave amplifier structurally arranged 'to insure proper alignment of Athe parts and the maintenance of design tolerances.

These 'and other features will become more .appa-rent from the nfollowing description :of 'a preferred embodiment of the present :invention as shown in the accompanying drawings wherein:

Fig. 1 4is an elevational .view of `a multi-cavity micro- 'wave amplifier, vparts Ibeing fcut .away to illustrate features of construction,

Fig. .2 `is 'a section taken along line 2-2 of Fig. l, and

=Fig. 3 is 'anfenlarged view partially inzsection illustrating interior construction of the resonator cavities of the amplier.

The microwave ampliierig'enerally Iincludes a beamproducing section. C10lfollowed 'hty 'a central section 11 wherein the interaction between the beam and the applied radio frequency wave takes place 'to provide the amplication and facollector section '12 where the electrons `of the spent Abeam are collected.

lin accordance with the invention, the amplification section 11 .of the tube preferably has a body formed from asubstantially semi-cylindrical :block 13 of/copper, as best illustrated in Fig. 2. A cylindrical bore 14 which extends longitudinally through the semi-cylindrical block 13 is intersected by a number of spaced transverse bores 15 extending from the flattened side 21 of the block 13 and is adapted to receive a plurality of drift-tube memice a bers 17. Each member 17 comprises a copper cylinder which 'is .provided with small cylindrical lextensions 18 at its ends Vand has a central bore extending therethrough and through Vsuch extensions to provide a drift space 19 for "the electron beam. When the members 17 are inserted inthe bore 14 in properly spaced relation, as determined by the spacing of the transverse bores 15, resonator cavities 16 of the desired frequency are formed between adjacent members. Prior to insertion of the copper drift-tube members 17 into Vthe bore 14, the latter is provided 'by a'liash-plating technique with a thin layer of silver. 'The exterior Vdimension of the drift tube members 17 is slightly greater than the diameter of the plated bore 14 through the described semi-cylindrical block 13 so that upon insertion .a pressed-fit is obtained. After the insertion of the drift tube members 17, a single heating operation will cause the copper and silver Vto alloy and the members to be fused within the bore. It should be lnoted that the same fusing technique and resulting assembly can be employed with drift tube members 17 which are not of solid copper construction; for example, copperclad molybdenum drift tube members can be utilized in the fabrication. This technique obviously avoids the mentioned diliiculty of conventional brazing methods and a clean juncture is formed between the drift tube members 17 and the bore 14 which provide, in effect, the walls ofthe resonator cavities 16.

An inner drift tube member 17 which is machined to provide the theoretically' desiredgeometry to as close tolerances as possible is .first inserted and, 'in turn, each of the adjacent drift tube members 17 is inserted to an extent slightly less than that required to provide the spacing productive of the desired resonant frequency of the cavities 1'6. Subsequently, radio frequency energy is .supplied to each cavity 16 between adjacent drift tube members through the respective one of the transverse bores V15 extending Vfrom the Viiattened-side 21 of the semi-,cylindrical .block 13. While radio frequency energy of .the desired frequency is inserted through the transverse bore 15 a Vslight axial movement is imparted to the drift tube member 17 until the resonance condition is achieved, vthis then being the final disposition of the member. The above described technique has been found not Vonly desirable but Vactually indispensable to vproduce the desired -cavity dimensions when operating at frequencies between 2O and 30 kmc. because at such frequencies :normal machining operations have insufficient accuracy to effect the desired structural tolerances.

AAs is shown clearly in Fig. 3, the first and last cavities 16 of 4the illustrated five-cavity amplifier are completed by members 17 which in effect constitute onehal-f ofthe complete drift tube members 17 previously described, in the intermediate portions of the bore 14.

To .provide coupling of radio frequency energy into and out ofthe amplifier, the described semi-cylindrical block 13 is -cut away in its lower portion for the reception of conventional waveguide sections 22 which cornmunicate with the first and last resonator cavities 16 through bored iris openings 23. A mica window 2.4 is suitably Asecured at the end of each of the waveguide sections 22 to maintain the vacuum within the cavities 16 and the remainder of the tube.

The ,previously mentioned bores 15 are enlarged adjacent the flattenedside 21 of the semi-cylindrical block 13 `as vindicated at 20 to receive in vacuum-tight relation a `tuning diaphragm 25 secured at the end of a tuning screw-'26 which is adjustably suspended from the lateral arrnj27a of a bracket 27 secured vto the flattened side 21 of the block 13 by suitable screws 28. The diaphragms 25 are maintained in adjusted position by pairs of lock nuts 29, 30 on the tuning screws 26 which nuts engage 3 respectively the upper and lower surfaces of the lateral bracket arm 27a.

The beam-producing section includes a substantially cylindrical hollow body 31 having a cathode button 32 and associated heater element 33 and focusing ring 34 mounted centrally therein and axially aligned with a tapered bore 35 formed in the base of an attached pole piece 36 of magnetic material and adapted to register with the aligned drift spaces 19 in the drift-tube members 17, 17' within the amplification section 11 of the tube. To assure that such alignment is achieved, the cathode button 32 is provided with a small central aperture 32a which enables the cathode 32 and the drift tube members 17, 17 of the tube to be aligned optically; that is, a light may be positioned at the end of the beam-producing section 10 and the same laterally shifted until such light passes through the small central aperture 32a in the cathode button 32, the registering bore 35 in the pole piece 36 and the drift tube members 17, 17 so as to be visible to a viewer whose eye is adjacent the drift space 19 at the output end of the amplification section 11. While so aligned the beam-producing section 10 or more particularly the attached pole piece 36 is aunularly brazed or otherwise secured to the amplication section 11 of the tube so that the alignment will be maintained.

The collector section 12 of the electron discharge device is preferably mounted on the second cup-shaped pole piece 38 having a tapered bore 39 extending centrally through its base and adapted to register with the aligned drift spaces 19 when said cup-shaped element is brazed in position at the output end of the amplification section 11 of the tube so as to accommodate the electron beam. Such alignment is again attained by the optical technique described above. The collector section 12 includes an elongated member 40 having a deep cylindrical recess 41 machined therein and arranged so that its open end is adjacent and axial with the tapered bore 39 in the pole piece 38. The two elements are secured in such relation through a glass-to-metal seal 42 formed between tubular stubs 43, 44 extending in opposite directions from an annular cap 45 on the cup-shaped pole piece 38 and a thick sleeve 46 telescoped onto the outer end of the elongated collector member 40. This construction and insulated mounting of the collector enables current readings to be taken when desired.

Tubulations 47 in the side of the two pole pieces 36, 38 enable evacuation of the tube after completion of the assembly, and are then pinched-off as shown in Fig. 1. To facilitate evacuation, eccentric axially-extending passages 48 are formed in the drift tube members since the actual diameter of the ldrift spaces 19 will be somewhat less than .02l at the mentioned operating frequencies. Because these passages 48 are relatively well below cutoff at the operating frequency, no radio frequency energy can be transmitted therethrough.

The tube is electrically connected quite conventionally, a battery 50 being arranged, as shown in Fig. 1 to provide heater current, and a second battery 51 to provide positive D.C. voltage `for the central and collector sections 11, 12 of the tube. Conventional coils indicated at S2, 53 are disposed adjacent the pole pieces 36, 38 to provide for proper focusing of the beam during its traverse through the tube. In operation, the beam of electrons emitted from the cathode button 32 is accelerated through the bore 35 and into the small cylindrical bores through the drift tube members 17. The radio frequency signal to be amplified is fed into the first or buncher cavity resonator through the input waveguide 22. The radio frequency electric field produced across the resonator gap in this first cavity resonator velocity modulates the electrons, that is, the electrons are slowed down or speeded up depending on the phase of the radio 4 frequency field across the gap at the time of transit of the electron. In the held-free drift space defined by the rst drift tube member 17 and extensions 18, the velocity modulation forms the beam into groups or bunches of electrons which, at their point of sharpest bunching, pass through the resonator gap in the second cavity resonator. All of the cavity resonators are so proportioned as to size and gap spacing as to be sharply resonant at the desired operating frequency of this cascade amplifier. The cavity resonators are initially tuned during assembly by the proper positioning and brazing of the drift tube members 17 to establish lcorrect resonator gap spacing, the cavities thereafter being fine-tuned by means of the ycliaphragrns 25. All of the cavity resonators between the rst or input resonator and the last or output resonator serve to improve the bunching of the electron beam initiated in the first cavity resonator so that optimum bunching is produced before the beam passes through the resonator gap in last or output resonator. The arnplifled radio frequency energy is passed out from this cascade amplifier through the output waveguide 22. An actual tube which has been constructed and operated with 1500 volts on the sections 11, 12 has produced a gain of as high as 74 decibels, as a result of the minimization of losses through the described arrangement in accordance with the invention. What losses do occur, of course, appear as heat in the amplification and collector sections 11, 12 of theV tube and are easily dissipated because of the large volume of the semi-cylindrical block i3 and the thick sleeve 46 on the collector member 40, no cooling fins being requireda Since many modifications and variations in the described arrangement can obviously be made without departing from the scope of the invention, it is intended that all matter in the foregoing description or shown in the drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. An electron discharge device comprising an electron beam-producing section, an electron collecting section, a. microwave amplification section disposed between said first and second named sections comprising a metallic body with a longitudinal bore extending therethrough, a thin layer of high electrically-conducting soldering material coated on the surface of the bore, and a plurality of drift tube members disposed within said bore in spaced relation whereby a plurality of resonator cavities are formed therein the drift tube members being secured within the bore fused to said layer of electrically-conducting soldering material, said drift tube members having axial bores therein through which said beam passes and having eccentrically disposed passages therein parallel to said axial bores and of dimensions such that the transmission of energy of the resonant frequency of said discharge device through said passages is precluded.

2. An electron discharge device according to claim 1 wherein said drift tube members are of copper and the coat on the surfacel of a said bore is a thin layer of silver.

References Cited in the lc of this patent UNITED STATES PATENTS Jimenez May 3l, 1955

Images