US2945983A

US2945983A - Electrode support for electron discharge devices

Info

Publication number: US2945983A
Application number: US811121A
Authority: US
Inventors: Herbert H Chun; Louis W Roberts
Original assignee: Bomac Laboratories Inc
Current assignee: Bomac Laboratories Inc
Priority date: 1959-05-05
Filing date: 1959-05-05
Publication date: 1960-07-19
Anticipated expiration: 1977-07-19

Description

July'l9, A1960 ELECTRODE SUPPORT FOR ELECTRON- DISCHARGE DEVICES Filed May 5, 1959 v l.INVENTORS HERBERT H. CHUN YLOUIS W. ROBERTS ATTORNEY H; .al CHUIQ ,mL 2,945,983

2 Sheets-Sheet 1 July 19, 1960 H. H. cHuN :TAL K ELECTRODE SUPPORT FOR ELECTRON DISCHARGE DEVICES. Filed may s, 1959 2 sheets-sheet 2 I ...sflabf 3 l 2 n L 69 7 32 3 e O a e m l L. 55 i 2 l 2 ,f 17H B p,//f//f/ 3 L l l .l a s\ l .h w 33 7- ...nh vT 3 FIG. 2

INVENTORS 'HERBERT H. CHUN BY LOUIS w. ROBERTS ATTORNEY ELECTRUDE SUPPORT FOR ELECTRON DISCHARGE DEVICES Filed May 5, 1959, Ser. No. 811,121

Claims. (Cl S15-39.3)

The present invention relates generally to electron discharge devices of the backward wave oscillator and/or amplier type and more particularly to an improved electrode structure for such devices.

Backward wave tubes of the Carcinotron -type generally comprise spaced parallel conductors `defining therebetween an interaction space. An electron beam emitted by a suitable gun source traverses the interaction space and is influenced by a crossed electric and magnetic iield established between the conductors. A delay line comprising interdigital metallic fingers forms one of the boundaries of the interaction space while the sole electrode forms the other boundary. Biasing voltage differentials provided by the parallel conductors as well as a grid and accelerator electrode control the electron beam configuration and the tube operation.

Generally it is considered that the sole electrode must be perfectly symmetrical with respect to an interdigital delay line for optimum tube performance. For various reasons, however, it has been observed that lthe symmetrical position may not `be the most desirable electrically from tube to tube. In the normal steady state operation of backward wave oscillator tubes, it is assumed that a balance of the electric and magnetic forces exists at every .point in the electron beam and that the beam current ilow. is rectilinear. It is noted, however, that the electric field between the sole electrode and the anode varies because of the charge on the beam. It therefore, follows that it is impossible to predetermine the critical placement of the sole electrode with respect to the delay line circuit due to a lack of control of the charge dis-V tribution in the beam at any arbitrary point in its path.

Itis an object of the present invention to provide means to externally optimize electrical performance of a backward wave oscillator and/or amplifier tube.

A further object of the invention is to provide an improved electrode structure for a backward wave oscillator and/ or amplifier tube to facilitate external adjustment of the electrode after completion of tube fabrication. v

A still further object is lto provide an improved sole electrode support for a backward wave oscillator and/or amplifier tube which may be readily adjusted after completion of fabrication to increase efficiency and power output.

The embodiment of the invention will be described with reference to a backward wave structure of circular conguration found in a Carcinotron It may be presumed that perfectly concentric spacing will produce optimum electrical characteristics. With experience gained in manufacturing, however, it has been noted that beam current characteristics may vary from tube to tube. In accordance with the teachings of the invention we provide an adjust- States Patent() lCe ing mechanism coupled directly to the sole electrode by means of a non-magnetic metal member attached thereto. The sole electrode may be moved axially and also radially by a simple manipulation of the adjusting mechanism which may be achieved externally after the tube has 'been completely fabricated and evacuated. It is a feature of the invention that the tube may be operated and then adjusted for optimum'performance electrically.

The advantages of the invention include increased efficiency over a selected frequency band as compared to pre-positioned prior art electrode structures as well as increased power outputs of from 20% to 100% over the band as compared with tubes not incorporating the adjustable electrode structure. Furthermore, holes and power dips haveA been considerably reduced across the frequency band and a tube having improved resistance to vibration and shock has resulted from the novel structure for mounting of the sole electrode.

Additional objects, features and advantages will be apparent after consideration of the following detailed description and -the accompanying drawings, in which:

Fig. l is a perspective view of the illustrative embodiment with a portion of the magnet structure broken laway to reveal the internal structure; y

Fig. 2 is a detailed cross-sectional view along theline 2 2 in Fig. 1 with the magnets omitted, and

Fig. 3 is a detailed plan view along the line 3-3 in Fig. 2. Y I

Referring to Fig. l the embodiment of the invention 1 comprises a circular metallic body member 2 enclosed by topand bottom` cover plates 3 and 4 tovthereby define a vacuum tight envelope. Before proceeding to a descrip'- tion of the structure within the envelope it may be noted that oppositely disposed toroidal magnets 5 and 6 surround the envelope to provide the magnetic eld for operation of the tube.

Spaced within the envelope is a `circular' metallic conductor comprising an interdigital delay line 7 having opposed iingers 8 and '9. extending from ring member 10 and 11. The delay line assembly is secu-rely positioned by means of a shoulder or step 12 and l'in body member 2', Concentrically disposed within the delay line structure is the sole electrode 14 which is supported by the improved adjust-ing mechanism of the invention now to be described.

The sole electrode 1.4 fabricated of a highly conductive oxygen-free metal such as copper forms together with the delay line 7 an interaction space :15 which is highly critical in the performance of backward wave tubes. With the delay line and body member at ground potential and the sole electrode-at a higher negative potential with respect to the cathode of the electron gun, an elect-ric eld is established in the interaction space. By adjusting the sole electrode spacing While the tube is operating it will be possibleto optimize performance. The sole positioning mechanism comprises a rigid spider member 16 secured at spaced intervals to the sole electrode by means of screws 17, 18,19 and 20. A non-magnetic metal, such as stain'- less steel is desirably employed for the spider member, as well as the screw members.` The central portion 21 of spider member 16 is secured to a ribbed sleeve 22 of an insulatingV material such as a ceramic having a highy alumina content. The sleeve 22 breaks the direct current contact between the sole electrode and the external ad; justing mechanism for positioning this electrode.

The central portion of the ceramic sleeve is in turn secured to a metallic adjusting rod 23 having one end hollowed as at 24 and the other end drilled and tapped as at 25. A deformable assembly is secured to the adjusting rod 23 comprising a two piece bellows diaphragm in which the inner member 26 is brazed to a shoulder on the rod and the outer member 27 is brazed to metallic cover plate 3 by means of cup 28. The two members of the deformable assembly are brazed together by a radio frequency induction technique to provide a vacuum joint and the metal employed is desirably Monel.

The adjusting mechanism is positioned external to the tube envelope and is supported by a collar or housing member 29. An adjusting screw 32 having a left-hand thread 33 and right-hand thread 34 is threaded into the end 25 of rod 23. The opposite end of screw 32 extends through housing member 29 and threadably engages a push-pull plate 50 Amounted on top of the housing member. Both the plate S and housing member 29 are secured to cover plate ,cup 28 by means of locking screws 30 and 31. Set nut 5-1 threaded at the endof rod 23 provides a secure bearing against the push-.pull plate l50. A recess 35 in the head of screw 32 provides means for introduction of an appropriate tool'to thereby produce axial movement of screw 32 which is translated into movement of the sole electrode along the plane of the magnetic eld of the device.

Within housing member 29, we next provide passageways spaced 90 apart with threaded centering pins'36 therein. Ball bearings 37 are also .provided the housing member to contact the tapered portion of each pin 36. A split Aring 38 attached to rod 23 also provides contact with the ball hearings 37. Movement of pins 36 in and out of the .housing passageways will then result in radical displacement ofthe sole electrode.

Cylindrical magnetic pole piece 39 Vsurrounds the ,housing member 29 and is secured to cover plate 3. Thermagnet contacts the pole piece to form apart of-the overall tube magnetic circuit.

The cathode electrode or electron gun assembly `cornmonly found in backward wave .oscillator tubes is positioned within a segment of the sole electrode and leads 40 extend through an insulated connection plate 41 to the cathode and sole input vassembly 4Z. A hollow conductive pipe 43 is connected to the sole electrode at one end and a ceramic insulator 44 `at `the other end. A conical cup 45 `is brazed to insulator 44 and welded by another flanged cup 46 secured to cover plate 4 to thereby provide a vacuum tight envelope.

The output coupling assembly 47 isintroducedinto the envelope and communicates -wth the delay line ngers in the manner well-known in the alt. The overall tube assembly is evacuated after all brazing and welding operations are completed by a suitable tubulation (not shown) which may be inserted through one of the cover plates.

After the tube has been completed, the appropriate electrical leads are connected and the electrical performance may be evaluated. A simple adjustment of the four radially disposed studs 36 or the screw 32 will then provide for radial as Well as axial adjustment of the sole electrode to optimize the electrical performance. Results of tubes incorporating the novel electrode positioning mechanism have shown `a to 100% increase in power output over a selected frequency bandpass oompared with tubes not incorporating this structure. Elimination of power dips or holes as they are sometimes referred to, `have been experienced ina substantial number of tubes. Vibration and shock requirements have also been lmet.

By way of illustration the following results have been tabulated showing electricaldata of a Carcinotron tube operated before and after adjustment of the sole electrode. v

1 Power below minimum.

While a specific illustrative embodiment has been described, many alterations or modifications will be evident to skilled artisans. lt is our intention to cover such alterations or modifications as fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. In an electron discharge device of the circular backward wave type comprising a cylindrical body member having end closure members disposed normal to the axis of the cylinder to define an envelope, concentrically disposed conductors enclosed within said envelope including a circular multifingered interdigital delay line supported by said body member and an inner negatively biased electrode spaced from said delay line to define an interaction space, said inner electrode being externally adjustable by mechanical means supported by an end closure member, said mechanical means comprising a metallic member of non-magnetic metal secured to a planar surface of said inner electrode, a non-conductive member secured to said metallic member, a rod secured -to said metallic member and extending axially through an end closure member, a deformable bellows structure joining said rod and end closure member to provide a vacuum tight seal, an adjusting mechanism secured to the top wall of said end closure member and communicating with the external end of said rod, said adjusting means cornprising a plurality of radially disposed ball bearing members and means for moving said bearing members normal -to the envelope axis to thereby contact said rod and displace said inner electrode radially and screw means threadably engaging the external end of said rod to axially displace Vsaid inner electrode to thereby alter the concentric alignment between said circular delay line and said inner electrode and optimize the electrical characteristics of the device.

2. An electron discharge device according to claim l wherein said screw means are provided with a left hand and a right hand screw thread.

3. An electron discharge device according to claim i wherein said non-magnetic metallic member is secured to -said electrode at a plurality of spaced points.

4. An electron discharge device according to claim l wherein said deformable bellows structure comprises a pair of inverted cup members joined together along a common wall.

5. An electron discharge device according to claim l wherein said means for moving said ball bearing members comprise threaded pins each having a tapered portion in contact with a ball bearing member.

References Cited in the tile of this patent UNITED STATES PATENTS 2,468,152 Woodyard Apr. 26, 1949 2,506,955 Fracassi May 9, 1950 2,786,959 Warneclie et al Mar. 26, 1957 2,878,412 Lally Mar. 17, 1959 2,888,597 Dohler et al. May 26, 1959