US3078385A

US3078385A - Klystron

Info

Publication number: US3078385A
Application number: US444582A
Authority: US
Inventors: Harold E Sorg; Donald H Preist; Richard H Chamberlin
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1954-07-20
Filing date: 1954-07-20
Publication date: 1963-02-19
Anticipated expiration: 1980-02-19
Also published as: CH337955A; DE1155864B; GB780825A; NL199045A; FR1127784A

Description

Feb. 19, 1963 H. E. soRG ETAL .KLYSTRON Filed July 20, 1954 IN V EN TORS Haro la E. Sor

United States Patent Odiice Patented Feb. i9, 1963 3,078,385 KLYSTRN Harold E. Sorg, Redwood City, Donald H. Preist, Mill Valley, and Richard H. Chamberlin, San Bruno, Calif.,

assignors to Eitel-McCullough, Inc., San Bruno, Caiif.,

a corporation of California Filed .lilly 20, 1954, Ser. No. 444,582 4 Claims. (Cl. S15- 5.43)

Our invention relates to electron tubes of the beam type such as klystrons and more particularly to klystrons having integral cavities wherein the entire cavity resonator is formed as part of the evacuated envelope.

It is among the objects of our invention to provide a klystron having an improved cavity resonator structure which provides a wide tuning range.

Another object is to provide a klystron in which the cavity resonator is a simple cylinder disposed transversely of the drift tube axis and incorporating a tuning plunger which is convenient to adjust and permits the desired degree of movement to give the wide tuning range.

Still another object is to provide a klystron of the character described which is easy to fabricate and assemble.

A further object is to provide a simplified mechanism for moving the tuning plunger.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawings:

FGURE l is an axial view, partly in section and partly in elevation, showing a three-cavity klystron embodying our invention; and

FIGURE 2 is a sectional View taken in a plane indicated by line 2-2 of FIGURE 1.

FGURE 3 is a detail sectional view of one of the cavity resonators showing the arrangement of parts during exhaust of the klystron.

In its preferred form our improved klystron comprises an elongated generally cylindrical envelope having an electron gun structure 2 at one end and a collector electrode assembly 3 at the other end. The electron beam from the gun to the collector passes through a drift tube made up of sections 4, 6, 7, and 8 of a metal such as copper extending axially of the envelope and having gaps 9 therebetween. The gaps are bridged by cavity resonators il. hereinafter described in detail.

Electron gun 2 comprises a cathode l2 housed in a cupshaped anode 13, say of copper, having an aperture .t4 ahead of the cathode and opening into drift tube section 4. Electrons from the cathode are focused through the anode aperture by a suitable focusing electrode i6. The entire gun assembly is mounted on a suitable stem 17 at the end of the envelope providing terminals for the cathode structure.

Collector 3 at the opposite end of the envelope comprises a cup-shaped electrode 1S connected to the end of drift tube section 3 so that the energy of the beam is dissipated at such collector electrode. The collector is cooled by a suitable water jacket 19 or the like.

T' ne above described elements of the electron tube function in the conventional manner for klystron tubes of this type, namely, the electron beam from gun 2 is accelerated by a positive potential on anode 13 and passes through the drift tube, past the interaction spaces provided by gaps 9, and iinally terminates at collector electrode 18. The three cavity resonators 11 coacting with the interaction spaces provided by gaps 9 serve as the frequency determining elements of the device. In the three-cavity klystron illustrated, functioning as an amplifier, the radiofrequency input is fed into the first resonator and the output is taken from the third resonator by coupling means later described.

Our improvements relate primarily to the cavity resonators 11 which are formed as a structurally integral part of the evacuated envelope. These resonators comprise simple metal cylinders 21, say of copper, so disposed that the axes of the cylinders are at right angles to the axis of the drift tube. Such cylindrical cavities are mounted on the drift tube sections so that the cavity resonators bridge gaps 9, the drift tube sections projecting into the central portions of cylinders 21 and being connected thereto at brazes 22. It is thus seen that the drift tube sections form side walls of the evacuated envelope along the axis, and that the cylinders 21 form additional walls of the evacuated envelope at the regions of the gaps. Since the cavity resonators are simple open-ended cylinders at the time the klystron is assembled, it is also seen that the structure is extremely simple to fabricate and assemble.

Means are provided in the cylindrical cavity resonators for tuning the same to adjust the operating frequency, which tuning means in our structure permits adjustment over a relatively wide band of frequencies. For this purpose we incorporate circular tuning plungers 23 in the end portions of each cylinder 21, at opposite sides of gap 9, so that the plungers provide movable walls to change the eifective size of the resonator. These plungers have diskshaped ends facing each other across the drift tube and also preferably have cylindrical side wall flanges 2.4i spaced from and extending rearwardly along the cavity cylinder 21 a suicient distance (approximately a quarter wavelength in the operating frequency range) to provide radiofrequency chokes. This effectively confines the RF tield and without having to require sliding contact between the plungers and the wall of cylinder 2l.

A flexible wall member 26, preferably a cylindrical corrugated metal bellows, is connected at one end to plunger 23 and at the other end to the outer end of cavity cylinder 21 to provide a vacuum-tight wall therebetween. This bellows has a fairly large diameter, preferably to just tit within the plunger flange 24. An apertured end plate 27 is fastened to the open end of cylinder Zi., secured at brazed joint 25. The bellows is brazed to this plate at 29 and to the plunger at braze 3l, which completes the vacuum-tight wall portions of the envelope structure.

The tuning mechanism for moving plunger 23 relative to gap 9 also functions as a supporting structure for the plunger and preferably comprises a pair of slidable telescoping guides 32 and 33, the outer tubular guide 33 having a flange 3d screwed to the apertured end plate 2.7 and the inner guide 32 having a flange bolted to the face of plunger 23. The aperture in end plate 27 is large enough to permit insertion and Withdrawal of the tuning mechanism. A feed screw 36 threaded in guide 32 is journaled in flange 34 and carries an adjusting knob 37 located exarge deinches or so, to allow tuning over a wide band of frequencies, which heretofore has been one of the limitations in integral cavity type lrlystrons. For example, in a lilystron having a center frequency of i380 mc. we have been able to achieve tuning over a band of 1200 to 1490 me. Another advantage of our structure is that the frequency adjusting mechanism worxs on an axis which extends radially of the main tube axis, thus being out in the open and free of space limitations and also locating the external working parts such as adjusting knobs in positions for maximum convenience of operation. l

Still another advantage of our improved klystron is that it can be adequately heated for outgassing the parts during exhaust, without danger of harming the tuning mechanism. When our tube is put together, all parts are assembled except the mechanical tuning unit comprising parts 32-37. At this time the plunger is in fully extended position, resting against the dritt tube sections as a stop and held by a holder 33 which temporarily replaces the tuning unit asV shown in FlGURE 3. With the plungers so held, the klystron structure can be elevated to the desired outgassing temperature, say 500 C. or more, during evacuation on the pump. After exhaust the holders 38 are replaced by the final tuning mechanisms.

As previously mentioned, the cavity resonators are simple cylinders brazed tcthe drift tube sections. Since the latter are xed solidly to the resonator cylinders and all tuning is done by the plungers 23 which are in the end portions of cylinders 2l, it is seen that the drift tube spacing at gap 9 is not altered in any way during tuning adjustment. This is important because optimum performance and eiliciency in a lily/stron of this type is achieved with a iixed spacing at the gaps.

The radio-frequency coupling into and out of the resonators is accomplished in a suitable manner, as by a loop couplings. FlGURE 2 shows such a coupling 39 for feeding the RF drive into the first resonator, the loop preferably being arranged alongside the drift tube and in the plane of the tube axis. For this purpose a coaxial line enters the side wall of the cavity cylinder, comprising an outer tubular conductor fil brazed to cylinder 2l and an inner conductor l2 passing through a vacuumtight seal and termn ung a loop A, similar coupling is provided at the third resonator for the RF output. Valli-ile we have shown a three-cavity type lilystron, it is understood that two or more than three resonators may be employed.

in operation of our ldystron the electron beam is maintained in an axial path down the dritt tube by suitable magnetic means (not shown) which may simply comprise el otro-magnet coils coa :Tally disposed about the envelope as is conventional practice in lilystrons of this type.

We claim:

l. A lrlystron comprising a d 'it tube having sections with a gap therebetween, a cavity resonator bridging the gap and comprising a cylindrical cavity with its axis disposed at right angles to the dritt tube axis, the entire resonator forming part of the envelope, a circular tuning plunger in the cavity resonator along side the gap, said tuning plunger having a diameter slightly smaller than the diameter of said cavity resonator and having a cylindrical side wall spaced irc-rn and extendinv along the cylindrical cavity forming an open-ended coaxial transmission lin having a length approximately equal to the quarter-wavelength in the operating frequency range of said klystron to provide a radio-frequency choice, the axis of said plunger being aligned with the axis of said cylindrica cavity, said plunger acting as an electrical endwall conlining the radio-frequency field in said cavity, and means exterior of said envelope for moving said plunger along its xis and for maintaining said side wall of said plunger l spaced from the cylirlrical inner wall of said cavity whereby all moving parts in said envelope are spaced from all other parts.

2. A lilystron comprising a drift tube having sections with a gap therebetween, a cavity resonator bridging the gap and comprising a cylindrical cavity with its axis disposed at right angles to the dritt tube axis, the entire resonator forming part oi the envelope, a circular tuning plunger in the cavity resonator along side the gap, said tuning plunger having a diameter slightly smaller than the diameter of said cavity resonator and having a cylindrical side wall spaced from and extending along the cylindrical cavity forming an open-ended coaxial transmission line having a length approximately equal to a quarter-wavelength in the operating frequency range oi said klystron to provide a radio-frequency choke, the axis ol` said plunger being aligned with the axis of said cylindrical cavity, said plunger acting as an electrical endwall conlining the radio-frequency field in said cavity, a cylindrical bellows in said cavity and coaxial therewith, the end of said bellows being connected to the plunger and the outer end of said bellows being connected to the outer end of the cavity resonator to provide a vacuum-tight wall therebetween, and tuning mechanism disposed outside the Vacuum envelope and projecting into the bellows from said outer end of the cavity resonator for supporting the plunger in spaced relation from said cavity resonator and for moving the plunger relative to said gap.

3. A klystron comprising a drift tube having sections with a gap therebetween, a cavity resonator bridging the gap and comprising a cylindrical cavity with its axis disposed at right angles to the drift tulbe axis, the entire resonator forming part of the tube envelope, a tuning plunger in the cavity resonator along side the gap and saving a cylindrical side wall spaced from and extending along the cylindrical cavity forming an open-ended coaxial transmission line having a length approximately equal to a quarter-wavelength in the operating frequency range or said klystron to provide a radiofrequency choke, said tuning plunger having a diameter slightly smaller than the diameter of said cavity resonator and acting as an electrical endwall confining the radio-frequency field in said cavity, a cylindrical bellows connected to the plunger and the outer end of the cavity resonator to provide a vacuum-tight wall therebetween, and tuning mechanism disposed outside the vacuum envelope and projecting into the bellows from said outer end of th resonator for supporting the plunger in spaced relation from said cavity resonator and for moving it relative to said gap, the tuning mechanism comprising a pair of slidable telescoping supporting guides connected to the plunger and said outer end of the cavity resonator and a feed screw journaled at said outer end.

4. A klystron comprising a drift tube having sections with a gap therebetween, a cavity resonator bridging the gap and comprisinv a cylindrical cavity wifn its axis disposed at right angles to the drift tube axis, the entire resonator forming part of the tube envelope, a tuning plunger in the cavity resonator along side the gap and having a cylindrical side wall spaced from and extending along the cylindrical cavity forming an open-ended coaxial transmission line having a length approximately equal to a quarter-wavelength in the operating frequency range of said klystron to provide a radio-frequency choke, said tuning plunger having a diameter slightly smaller than the diameter of said cavity resonator and acting as an electrical end-wall conlining the radio-frequency iield to said cavity, a cylindrical bellows connected to the plunger and the outer end of the cavity resonator to provide a vacuum-tight wall therebetween, and tuning mechanism disposed outside the vacuum envelope and projecting into the bellows from said outer end or the cavity resonator for supporting the plunger in spaced relation from said cavity resonator and for moving it relative to said gap, the tuning mechanism comprising a pair of slidable telescoping supporting guides connected to the plunger and said outer end of the cavity resonator and a feed screw journaled at said outer end, said tuning mechanism being demountabiy supported at said outer end of the cavity resonator.

References Cited in the ile of this patent UNITED STATES PATENTS 6 Learned Aug. 5, 1952 Chodorow Nov. 4, 1952 Norton et al. Nov. 25, 1952 Eitel Feb. 17, 1953 Finke July 7, 1953 Varian Juiy 7, 1953 Ebers Sept. 8, 1953 Hewlett et a1 Sept. 15, 1953 Rich Feb. 1, 1955 Gardner et a1. Sept. 24, 1957 Coeterier Dec. 10, 1957 Bondley Oct. 27, 1959

Claims

1. A KYLSTRON COMPRISING A DRIFT TUBE HAVING SECTIONS WITH A GAP THEREBETWEEN, A CAVITY RESONATOR BRIDGING THE GAP AND COMPRISING A CYLINDRICAL CAVITY WITH ITS AXIS DISPOSED AT RIGHT ANGLES TO THE DRIFT TUBE AXIS, THE ENTIRE RESONATOR FORMING PART OF THE ENVELOPE, A CIRCULAR TUNING PLUNGER IN THE CAVITY RESONATOR ALONG SIDE THE GAP, SAID TUNING PLUNGER HAVING A DIAMETER SLIGHTLY SMALLER THAN THE DIAMETER OF SAID CAVITY RESONATOR AND HAVING A CYLINDRICAL SIDE WALL SPACE FROM AND EXTENDING ALONG THE CYLINDRICAL CAVITY FORMING AN OPEN-ENDED COAXIAL TRANSMISSION LINE HAVING A LENGTH APPROXIMATELY EQUAL TO THE QUARTER-WAVELENGTH IN THE OPERATING FREQUENCY RANGE OF SAID KLYSTRON TO PROVIDE A RADIO-FREQUENCY CHOKE, THE AXIS OF SAID PLUNGER BEING ALIGNED WITH THE AXIS OF SAID CYLINDRICAL CAVITY, SAID PLUNGER ACTING AS AN ELECTRICAL ENDWALL CONFINING THE RADIO-FREQUENCY FIELD IN SAID CAVITY, AND MEANS EXTERIOR OF SAID ENVELOPE FOR MOVING SAID PLUNGER ALONG ITS AXIS AND FOR MAINTAINING SAID SIDE WALL OF SAID PLUNGER SPACED FROM THE CYLINDRICAL INNER WALL OF SAID CAVITY WHEREBY ALL MOVING PARTS IN SAID ENVELOPE ARE SPACED FROM ALL OTHER PARTS.