US3720889A

US3720889A - Electron discharge devices

Info

Publication number: US3720889A
Application number: US00001747A
Authority: US
Inventors: F Gale
Original assignee: EMI Ltd
Current assignee: QED Intellectual Property Ltd
Priority date: 1970-01-09
Filing date: 1970-01-09
Publication date: 1973-03-13
Anticipated expiration: 1990-03-13

Abstract

An electron discharge device such as a klystron has a cavity resonator tuned by a plunger in a sub-cavity. The sealing of the sub-cavity is provided by means of a diaphragm which is shielded from electromagnetic energy by part of the choke-forming surfaces of a ditch choke. The shielding surface may be in the form of another diaphragm.

Description

United States Patent ['91 Gale l lMarch 13, 1973 ELECTRON DISCHARGE DEVICES [75] Inventor: Frederick Henry Gale, Hillingdon,

England [73] Assignee: EMI Limited, Hayes, Middlesex,

England [22] Filed: Jan.9,l970

[21] App1.No.: 1,747

[52] -U.S. Cl. ..333/83, 315/546, 315/5.48, 315/553 [51] Int. Cl. ..HOlp 7/06 [58] Field of Search ..315/5.46, 5.47.5.48.5.53; 333/83 [56] References Cited UNITED STATES PATENTS 2,853,647 9/1958 Litton ..315/5.47

3/1964 Ward ..333/83 3,l25,734 3,178,605 4/l965 Allen, Jr. et al ....3l5/5.46 3,240,983 3/1966 Biechler et al. ..3 l 5/5.48

Primary Examiner-Herman Karl Saalbach Assistant ExaminerSaxfield Chatmon, Jr. Att0rneyWilliam W. Downing, Jr.

[ ABSTRACT An electron discharge device such as a klystron has a cavity resonator tuned by a plunger in a sub-cavity. The sealing of the sub-cavity is provided by means of a diaphragm which is shielded from electromagnetic energy by part of the choke-forming surfaces of a ditch choke. The shielding surface may be in the form of another diaphragm.

8 Claims, 2 Drawing Figures PATENTEUMAR13 I975 SHEET 10F 2 FIG. I.

ELECTRON DISCHARGE DEVICES This invention relates to electron discharge devices having an integral resonant cavity and means for tuning said cavity.

It is known to provide an electron discharge device such as a high power amplifier klystron with resonant cavities and to vary the frequencies of these cavities by plungers which are moved in the cavities to change the volume thereof. Movement of the plungers in the cavities is usually axial and is effected by a screw and nut mechanism. The cavities are evacuated with the device, and movement of the plungers is permitted by coupling it to a bellows which in turn is sealed to the envelope of the device. To reduce losses of energy from the cavities it is usual to surround the plunger with a ditch type choke, part of which is formed by the bellows. The bellows are usually constructed of copper.

It has been found that in operation of a device of this kind parts of the bellows tend to be heated to a high temperature such that the side thereof which is exposed to the atmosphere oxidizes whereby rupture of the wall of the bellows occurs resulting in loss of vacuum.

It is an object of the invention to provide an improved electron discharge device in which the above disadvantage is alleviated.

According to one aspect of the invention there is provided an electron discharge device including an envelope provided with a cavity resonator, and tuning means movable within the cavity for tuning said resonator said tuning means being coupled to said envelope by a flexible member which can be deflected to allow movement of said tuning means without breaking the seal of the envelope, said tuning means and said envelope including spaced conductive surfaces forming a ditch choke having an electrical length of substantially M2 and having an intermediate region which runs adjacent said flexible member, and a shield part of said choke-forming surfaces being provided by a member disposed in front of said flexible member and separating the choke therefrom to shield said flexible member to a substantial extent from electromagnetic energy in said choke.

The flexible member may be an annular diaphragm having a series of concentric corrugations the peripheral portion of the diaphragm being sealed to the envelope of the device and the inner portion to a spindle connected to and supporting the plunger. The choke is formed as a ditch between the plunger and a part of the envelope wall which leads into the resonator this ditch continuing to the rear of the plunger. Part of the wall of the choke which is transverse of the plunger and which lies behind the plunger is formed as a further flexible diaphragm housed entirely within the vacuum space.

In order that the invention may be clearly understood and readily carried into effect it will now be described with reference to the drawings, in which:

FIG. 1 illustrates a part sectional view of a multiaccompanying cavity electron discharge device according to the input resonator 3 and therebetween a tunable intermediate resonator 4. In a device of this kind for operation with a wide pass band four intermediate tunable resonators would be provided. The intermediate resonator 4 is defined by the inner wall of the envelope portion 5 at the center of which is an interaction gap formed by the nib ends of the adjacent

drift tube parts

6 and 7. Extending through a wall of the resonator is an annular extension portion forming a sub-cavity 9 housing a plunger 10 which when moved axially can effect a variation in the frequency of the resonator by changing the volume thereof. The manner of mounting the plunger 10 will be further described with reference to the enlarged view of FIG. 2.

The plunger 10 is mounted centrally in the sub-cavity 9 so that it is spaced from the wall thereof. The rear of the plunger has a re-entrant portion 11 a cylindrical portion 12 and a central hollow spindle 13. The plunger 10 and the portion 12 may be formed of stainless steel and coated with copper. The portions 12 and 13 make sliding engagement with the outer and inner surfaces of an axially disposed sleeve 14 supported by a transverse wall 15. A screw threaded spindle l6 co-operates with a thread 17 on the portion 13 so that a rotation of the spindle 16 causes the plunger 10 to be moved axially within the sub-cavity 9. To provide a vacuum seal for the sub-cavity 9 and yet allow for axial movements of the plunger 10 a flexible member such as an annular diaphragm 18, provided with concentric corrugations is hermetically sealed at its inner periphery to the end of cylindrical portion 12 and at its outer periphery to a wall member 19 of the sub-cavity 9. The member 19 is in turn sealed in a hermetic manner to the end of the sub-cavity 9 so that the tuner assembly may be assembled as a unit. The diaphragm 18 may be conveniently formed of copper or copper nickel alloy and since it is located at a position where there is substantially no RF field this diaphragm remains relatively cool in operation. Spaced at a short distance from the diaphragm 18 is a second diaphragm 20 of similar construction and this is sealed to the portion 12 ofthe plunger at its inner periphery and to the wall member 19 of the sub-cavity 9 at its outer periphery. The diaphragm 18 is thus shielded from RF energy by the diaphragm 20 which differs from the diaphragm 18 in that it is provided with a small hole 21 so that it does not form a vacuum seal.

Electrical short circuiting of the plunger 10 and the inner wall of the sub-cavity 9 is by means of a radio frequency ditch choke of length M2 formed as two portions of M4 in series. The first M4 portion is formed by the axial space between the wall of the sub-cavity 9 and the plunger 10. The second M4 portion is formed by the rear surface of the plunger 10 and the re-entrant portion 11 thereof, the diaphragm 20.forming part of a wall of the second portion of the choke. Since the diaphragm 20 is located nearer to the M4 wave position which is at a current node or voltage antinode position it will not be unduly heated by RF currents therein. Since the diaphragm 20 is entirely within the vacuum of the device there is no possibility of its becoming oxidized should it become heated during operation of the device. As the diaphragm 18 forming the vacuum seal is located at a position where there is substantially no RF field the only chance of its becoming heated is by conduction from the plunger, and it has been found that this diaphragm remains at a temperature below 100 C throughout the operation of the device even under over-load conditions.

Making the M2 choke in two halves each M4 long but with different characteristic impedances provides the improvement that a low impedance (short circuit) can be transformed by a M4 high characteristic impedance into a very high impedance and this again if transformed through a )t/4 low characteristic impedance line results in a much lower impedance than a short circuit employing a normal M2 choke. This will make it appear that the ditch section of the tuning plunger is less resistive than the solid section of the tuner.

It is to be understood that the term envelope as used in the appended claims includes the wall portion 5 and the sub-cavity 9.

What I claim is:

1. An electron discharge device including an envelope provided with a cavity resonator, and tunable means movable within the cavity for tuning said resonator, said tuning means being coupled to said envelope by a flexible member which can be deflected to allow movement of said tuning means without breaking the seal of the envelope, said tuning means and said envelope including spaced conductive surfaces forming a ditch choke having an electrical length of substantially k/2 and having an intermediate region which runs adjacent said flexible member, and a shield part of said choke-forming surfaces being provided by a member disposed in front of said flexible member and separating the choke therefrom to shield said flexible member to a substantial extent from electromagnetic energy in said choke.

2. A device according to claim 1 wherein said shield part is in the form of a second flexible member coupling said tuning means to said device, said second flexible member being located in said region wherein a current node occurs in said choke.

3. A device according to claim 2 wherein said choke is substantially U-shaped with one surface of the base of the U formed by said second flexible member.

4. A device according to claim 3 wherein the two limbs of said U-shaped choke are formed respectively by a space between said tuning means and said envelope and by a re-entrant space in said tuning means.

5. An electron discharge device according to claim 1 wherein said shield part is in the form of a second flexible member coupling said tuning means to said device.

6. An electron discharge device according to claim 5 wherein said second flexible member is parallel to said first mentioned flexible member.

7. An electron discharge device according to claim 1 wherein the space between said flexible member and said shield part is in communication with said cavity.

8. An electron discharge device according to claim 1 wherein said shield part is located in or near a region wherein a current node occurs in said choke.

Claims

1. An electron discharge device including an envelope provided with a cavity resonator, and tunable means movable within the cavity for tuning said resonator, said tuning means being coupled to said envelope by a flexible member which can be deflected to allow movement of said tuning means without breaking the seal of the envelope, said tuning means and said envelope including spaced conductive surfaces forming a ditch choke having an electrical length of substantially lambda /2 and having an intermediate region which runs adjacent said flexible member, and a shield part of said choke-forming surfaces being provided by a member disposed in front of said flexible member and separating the choke therefrom to shield said flexible member to a substantial extent from electromagnetic energy in said choke.