US2910613A

US2910613A - Electron tube

Info

Publication number: US2910613A
Application number: US552576A
Authority: US
Inventors: George M W Badger
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1955-12-12
Filing date: 1955-12-12
Publication date: 1959-10-27
Anticipated expiration: 1976-10-27
Also published as: DE1128569B; GB562674A; NL67137C; FR1155168A; NL212892A; CH340912A; GB834664A

Description

Oct. 27, 1959 G. M.- W. BADGER ELECTRON TUBE Filed Dec. 12, 1955 I N VEN TOR. George MWBaager BY WM 6 W ATTORNEY from the drift tube.

United States Patent ELECTRON TUBE George M. W. Badger, San Bruno, Calif., assignor to Eitel-McCullough, Inc., San Bruno, Calif., a corporation of California Application December 12, 1955, Serial No. 552,576

4 Claims. 01. SIS-5.38)

velocity modulation of the beam. Conventional klystron construction comprises an electron gun at one end and a collector at the other end. The radio frequency structure between the electron gun and collector comprises a drift tube provided with a plurality of gaps intermediate its ends and. a cavity resonator surrounding each gap. Normally, each cavity resonator is equipped with tuning means for changing the effective size of the cavity, such tuning means being positioned either within the tube envelope or externally thereof.

In an amplifier klystron, to which the present invention relates, the cavity nearest the gun is the input cavity and is fed with radio frequency energy from a driving source at low level. The cavity nearest the collector is the output cavity and is tuned to resonance and coupled to a load. Preferably one or more cavities are provided intermediate the input and output cavities, and these intermediate cavities are tuned to resonance or near resonance but are not fed with energy from outside the tube. The purpose of the input and intermediate cavities, ,in conjunction with the drift tube sections; is to velocity modulate the electron beam so as to produce bunches of electrons at the output cavity. The output cavity then serves to. extract radio frequency energy from the bunched electron beam. 7

In addition to the elements mentioned in the preceding description, beam type tubes are provided with a magnetic circuit which, in the case of klystrons, normally comprises a plurality of electromagnets positioned outside thetube envelope to produce a magnetic field having lines of force directed axially of the, drift tube. Be-

cause of the mutual repulsion of electrons in the beam, the beam tends to expand as it travels down the drift tube and would strike the tube walls were it not for the constricting effect of the magnetic field. The optimum field strength is fairly critical and is not necessarily uniform along the length of the drift tube.

In order to facilitate proper adjustment of the magnetic circuit and optimum tuning of the cavity resonators,the collector in conventional klystrons is insulated Thus it is possible to monitor the direct current division between the collector and the drift tube sections and determine when the magnetic circuit and cavity resonators are properly adjusted to keep at a minimum the number of electrons striking the drift tube.

Klystrons constructed and operated in the manner electrodes.

2,910,613 Patented Oct. 27, 1959 summarized in the preceding description have been found to be inherently unstable; that is, they are subject to violent oscillations.

Accordingly, it is among the objects of this invention to provide a beam type tube in which inherent oscillations are substantially reduced or entirely eliminated.

In studying the problem of klystron oscillation, it was determined that the detrimental oscillations were caused mainly by feed-back of radio frequency energy which escaped from the collector. The radio frequency energy in the bunched electron beam is not entirely extracted at the gap in the output cavity, and there is some remaining energy which passes into the collector. As a result, the collector acts as an antenna to cause undesirable feedback.

Accordingly, a further object of the invention is to provide a beam type tube in which radio frequency energy in the collector is preventedfrom causing feedback.

The preceding objects are accomplished by providing a by-pass condenser between the collector and the remainder of the tube, and a further object is to provide such a condenser built into the tube envelope.

Another object of the invention is to provide an envelope structure forming a built-in condenser suitable for use in electron tubes in general as well. as in klystrons.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the invention. It is to be understood that the invention is not limitedto the disclosed species, as variant embodiments thereof are contemplated and may be adopted within the scope of the claims.

Referring to. the drawings:

Figure 1 is an axial sectional View of a 3-cavity klystron incorporating the condenser arrangement of the invention; and,

Figure 2 is an enlarged view showing the details of the condenser arrangement of Figure l.

Referring in more detail to the drawings, Figure 1 shows a beam type tube known as a klystron. The tube comprises an electron gun 3 at one end, a collector 4 at the other end, radio frequency structure 5 interposed between gun 3 and collector 4, and connecting means 6 between collector 4 and the radio frequency structure 5. Connecting means 6 is the essential feature of the invention and serves both as a by-pass condenser and as a portion of the tube envelope.

Electron gun 3 comprises a cathode 8 housed in a cupshaped anode 9 preferably made of copper. The anode is connected to the radio frequency structure 5 at a braze 10 toform an aperture 11 opening into the radio frequcncy structure. Electrons from the cathode are focused into the aperture 11 by a cylindrical focusing electrode 12. The entire gun structure is mountd on a suitable stem 14 which may be of conventional glass. and metal construction with suitable terminals for the various Collector 4 at the opposite end of the tube is simply a cup-shaped structure which is preferably made of copper and may be provided with suitable exhaust tubulation 15 and cooling structure not shown.

The radio frequency structure 5 comprises a drift tube formed by sections 16, 17, 18 and 19 of a metal such "wall disks 23 connected by a ceramic insulating cylinder 24. Walls 23, normally made of copper, are apertured to receive the drift tube sections and are fired to the latter at brazes 25.

Resonators 22 are preferably provided with tuning structures externally of the envelope. These tuning structures, one of which is indicated by the dotted lines accomplish additional velocity modulation of the beam.

The cavity resonator nearest the collector is known as the output resonator and is coupled to a load not shown.

The output resonator is tuned to resonance and serves to extract radio frequency energy from the bunched electron beam as it, passes across gap 20 of the output resonator.

The collector 4 is separated from drift tube section 19 to form a space 30 therebetween, and the connecting means 6 serves to connect collector 4 to the tube section 19. As shown best in Figure 2, connecting means 6 comprises a metal flange 31 projecting outwardly from the drift tube section 19 and a metal flange 32 projecting outwardly from the collector 4. These flanges are preferably made of copper and are secured in place by brazes 33. A ceramic insulating cylinder 34 is positioned between

flanges

31 and 32, with the ends of the cylinder being sealed to the flanges so that the connecting structure 6 actually is a part of the tube envelope and forms a vacuum-tight cover around the space 30. Various types of arrangements may be employed to seal the ends of cylinder 34 to the

adjacent flanges

31 and 32. The type of sealing arrangement shown in Figure 2 comprises outer rings 36 and inner rings 37. The rings are preferably made of copper, and the outer rings are brazed to the flanges. The inner rings are provided with inturned portions which overlap the ends of cylinder 34, and these inturned portions are bonded to the ends of the ceramic cylinder. In order to bond the inner rings 37 to the ceramic cylinder 34, the ends of the cylinder are first metalized by any suitable process. By way of example, the ceramic areas to be metalized can be coated with an 80%-20% mixture of powdered molybdenum and manganese in a suitable liquid vehicle and then fired in a reducing atmosphere at a temperature of about 1500 C. After the ends of the cylinder are metalized, the inturned portions of rings 37 are brazed to the metalized surfaces with suitable brazing material such as copper-silver eutectic. In order to relieve the sealing rings from the axial compressive force due to atmosphericpressure,

flanges

31 and 32 are provided with

rings

38 and 39, respectively, which abut the inturned portions of the inner rings 37. The type of sealing arrangement thus described for Figure 2 is also employed in the cavity resonators 22 to join ceramic cylinders 24 to the end plates 23.

In the form of the invention shown in the drawings, the by-pass condenser between collector 4 and the radio frequency structure 5 is incorporated in the connecting structure 6. In the disclosed embodiment the inner and outer surfaces of cylinder 34 are metalized as indicated at and 41, respectively, by the process previously described in connection with the ends of the cylinder. Preferably, the metalizing layers 40 and 41 are painted on the inner and outer sides of the ceramic cylinder at the same time that the ends of the cylinder are coated with the metalizing paint. Thus, there is a good electrical flow path from the inner metalizing layer 40 to the metalizing layer on the right end of the cylinder and then through the inner ring 37 to the flange 32 Similarly, there is a good electrical flow path from the outer metalizing layer 41 to the flange 31. It should be noted that neither of the metalizing layers 40 and 41 extends the full axial lengthof cylinder 34 so that there is no path through which direct current can flow between flanges 31 and Y32. The inner metalizing layer 40 is thus in electrical contact with flange 32 but is spaced from flange 31. Conversely, the outer metalizing 41 is in electrical contact with flange 31 but is spaced from flange 32. Preferably, the inner metalizing overlaps the outer metalizing and vice versa, as shown in Figure 2. The built-in condenser arrangement disclosed in Figure 2 is, of course, not limited to use in klystrons and may be incorporated in the envelope structure of any tube having metal envelope sections separated by an insulating section.

The required characteristics for the by-pass condenser formed by the metalized ceramic section 34 are that it have a high enough resistance to prevent flow of direct current from drift tube section 19 to collector 4 and that it have a low enough impedance to permit the flow of radio frequency current between drift tube section 19 and collector 4. Although the preferred condenser structure is the metalized ceramic type disclosed in Figure 2, any type of condenser having the preceding characteristics can be employed to reduce feedback and thus improve the operating stability of the tube. For example, a suitable condenser could be made by substituting metal cylinders for the metalizing layers 40 and 41. As will be understood by those skilled in the art, all of the drift tube sections, including section 19, are grounded during operation of the tube so that radio frequency energy in the collector is passed off to ground instead of causing feedback.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A klystron comprising a drift tube having a plurality of gaps along its length, a resonator adjacent each gap, an electron gun at one end of said drift tube, a collector at the opposite end of said drift tube, said collector being spaced from said drift tube to prevent flow of direct current from said drift tube to said collector, and connecting means joining said collector to said drift tube, said connecting means defining a portion of the tube envelope and comprising a ceramic section encircling said collector and said drift tube and forming a portion of the tube envelope and having metalized portions on the inner and outer surfaces and forming a by-pass condenser to permit the passage of radio frequency current from said collector to said drift tube.

2. A klystron comprising a drift tube having a plurality of gaps along its length, a resonator adjacent each gap, an electron gun at one end of said drift tube, a collector at the opposite end of said drift tube, said collector being spaced from said drift tube to prevent flow of direct current from said drift tube to said collector, connecting means joining said collector to said drift tube, said connecting means comprising a metal flange projecting outwardly from said drift tube, a metal flange projecting outwardly from said collector and spaced from said first mentioned flange, a cylindrical insulating section sealed between said flanges, a coating of electrically conductive material on the inside of said insulating section, and a coating of electrically conductive material on the outside of said insulating section, said inner coating being in electrical contact with one of said flanges and spaced from the other of said flanges, and said outer coating being in electrical contact with said other flange and spaced from said one flange, whereby said connecting means forms a condenser between said collector and said drift tube for isolating said collector from direct current in said drift tube and for permitting the passage of radio frequency current from said collector to said drift tube. 3. A klystron comprising a drift tube having a plurality of gaps along its length, a resonator adjacent each gap, an electron gun at one end of said drift tube, a collector at the opposite end of said drift tube, said collector being spaced from said drift tube to prevent flow of direct current from said drift tube to said collector, conmeeting means joining said collector to said drift tube, said connecting means comprising a metal flange projecting outwardly from said drift tube, a metal flange projecting outwardly from said collector and spaced from the first mentioned flange, a ceramic insulating cylinder sealed between said flanges, said ceramic cylinder being metalizecl on its inner and outer surfaces, the metalizing on the inside of said cylinder being in electrical contact with one of said flanges and spaced from the other of said flanges, and the metalizing on the outside of said cylinder being in electrical contact with said other flange and spaced from said one flange, whereby said connecting means forms a by-pass condenser for radio frequency current between said drift tube and said collector.

4. A klystron comprising a drift tube having a plurality of gaps along its length, a resonator adjacent each gap, an electron gun at one end of said drift tube, a collector at the opposite end of said drift tube, said collector being spaced from said drift tube to prevent flow of direct current from said drift tube to said collector,

connecting means joining said collector to said drift tube,

said connecting means comprising a metal flange projecting outwardly from said drift tube, a metal flange projecting outwardly from said collector and spaced from the first mentioned flange, a ceramic insulating cylinder sealed between said flanges, said ceramic cylinder being metalized on its inner and outer surfaces, the metalizing on the inside of said cylinder being in electrical contact with one of said flanges and spaced from the other of said flanges, the metalizing on the outside of said cylinder being in electrical contact with said other flange and spaced from said one flange, and the metalizing on the inside of said cylinder overlapping the metalizing on the outside of the cylinder and vice versa, whereby said connecting means forms a by-pass condenser for radio frequency current between said drift tube and said collector.

References Cited in the file of this patent UNETED STATES PATENTS 276,571 Diehl May 1, 1883 1,222,916 Babcock Apr. 17, 1917 2,129,008 Kater Sept. 6, 1938 2,139,447 Ebinger Dec. 6, 1938 2,391,016 Ginzton Dec. 18, 1945 2,410,063 Hansen Oct. 29, 1946 2,416,565 Beggs Feb. 25, 1947 2,506,590 Hansen May 9, 1950 2,570,289 Tourton Oct. 9, 1951 2,619,611 Norton et a1 Nov. 25, 1952 2,628,328 Scullin Feb. 10, 1953 2,634,383 Gurewitsch Apr. 7, 1953 2,803,749 Andrews Aug. 20, 1957 FOREIGN PATENTS 452,573 Great Britain Aug. 25, 1936