US3564318A

US3564318A - Electrode support structure utilizing a corregated metal ribbon for accomodating thermal expansion

Info

Publication number: US3564318A
Application number: US810951A
Authority: US
Inventors: James E Beggs
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1969-03-27
Filing date: 1969-03-27
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16
Also published as: FR2033731A5

Abstract

A corrugated metal ribbon is attached between the outer circumference of a planar grid or cathode electrode and the interior opening of a contact member, the corrugated member accommodating thermal expansion differentials without distortion of the electrodes or contact members so that the electrodes that can be mounted and maintained in precise spaced relationship.

Description

United States Patent James E. Beggs Schenectady, N.Y. [21] AppLNo. 810,951

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3/1958 Cut1er...........

2,832,911 4/1958 VanVe1zer....

3,158,122 11/1964 DeGive......... 3,334,263

[22] Filed Mar. 27, 1969 [45] Patented Feb. 16, 1971 [73] Assignee General Electric Company 8/1967 Beggs.......................:::. Primary ExaminerRoy Lake Assis!an! Examiner-E. R. LaRoche n, Julius .1 n, Frank L. Neuhauser and Awe mmw

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ABSTRACT: A corrugated metal ribbon is attached between cc of a planar grid or cathode electrode g of a contact member, the corrugated ing thermal expansion differentials 14 Claims, 2 Drawing Figs.

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ELECTRODE SUPPORT STRUCTURE UTILIZING A COR- REGATED METAL RIBBON FOR ACCOMMODATING THERMAL EXPANSION ELECTRODE SUPPORT STRUCTURE This invention relates to high frequency electron discharge devices and, in particular, to a support for the electrode of such a device so that they can be operated over a broad power and temperature range without disturbing the precise spacing between the electrodes.

In my U.S. Pat. No. 2,680,824, assigned to the assignee of the present invention, a type of electron discharge device having planar electrodes is described and claimed, which device may be miniaturized in structure and provided with externally accessible ringlike terminals. These miniaturized discharge devices are useful at high frequencies because their electrodes are small in cross section and relatively closely spaced, thereby reducing interelectrode capacitance and electron transit time between electrodes. While this construction per- -mits operation at high frequencies, there is always the desire to obtain even greater power output at such high frequencies. To accomplish such an objective requires operating at still greater current densities at which the fine wires of the grid electrodes tend to distort because of the inability to adequately cool the grid. Consequently, it is desirable to obtain a struc ture inwhich heat is rapidly removed from the grid electrode to prevent such distortion and yet to provide a structure which allows accurate spacing of the grid electrode with respect to the cathode and which is not distorted when operating at high temperatures.

Another practice in building planar-type electron discharge devices is to mount the cathode on a cylinder of thin metal. When such a cathode is heated, the cylinder elongates and moves the cathode surface closer to the grid surface. To obtain high performance from such a device, it is necessary to operate with the cathode in close proximity to the control grid. This spacing is difficult to control if the cathode moves relative to the grid during operation of the tube.

Accordingly, it is a primary object of my invention to provide a new and improved electrode support structure for a planar-type electron discharge device which permits operation of the device at high temperatures while maintaining precise spacing relationships between the electrodes of the device.

It is another object of my invention to provide a new and improved electrode structure for a planar-type electron discharge device in which the cathode and control electrodes are supported by members which accommodate thermal expansion differentials without distortion of the electrodes or contact members for the electrodes.

The features and advantages which characterize my invention will become more apparent as the following description proceeds, reference being made to the accompanying drawing and its scope will be pointed out in the appended claims. In the drawing,

FIG. 1 is an elevation view, partly in section, of an electron discharge device embodying my invention; and

FIG. 2 is a sectionalperspective view of a portion of the device of FIG. 1.

In the preferred embodiment illustrated, the envelope of the device is made up of generally circular or annular metal and insulating members alternately arranged and bonded together to provide a hermetically sealed envelope. As illustrated in FIG. 1, the device includes a generally circular anode 1 having a planar electron-receiving surface 2 which is in opposed relation with the electron emissive surface of a cathode 3. Cathode 3 may be of the type described and claimed in my ;.U .S. Pat. No. 3,334,263, granted Aug. 1, 1967 and assigned to the assignee of the present'invention, and consists of a large mass cathode member having channels or recesses 4 for receiving transverse bars 5 of a control grid 6. Grid 6 includes a support frame in the form of a metal annulus 7 and a plurality of fine grid conductors 8 which are welded or otherwise attached to the annulus 7 and bars 5. Bars 5 are relatively massive compared to grid wires 8 and may be formed integrally with annulus 7.

The external portion of the envelope of the device is formed of a plurality of ceramic insulating cylindrical members bonded to metal cylindrical terminal members. The ceramic insulating members are desirably Forsterite because of its low dielectric constant, or a magnesia and magnesia-alumina spinel, such as disclosed in US. Pat. No. 3,1 13,846 Leschen, assigned to the assignee of this present invention. The

ceramic cylinders

10, 11, 12, moreover, have the same coefficient of expansion as a titanium flange 13 which is sealed between cylinder 10 and grid contact ring 14 which consists of any suitable contact metal, such as, for example, titanium.

Cylinder 11 is sealed between the lower surface of grid contact ring 14 and a cathode contact ring 15 which, likewise, may comprise titanium. Cylinder 12 is sealed between cathode contact member 15 and a heater contact member 16 which, likewise, may be formed of titanium. A pair of

conductors

17, 18 are connected respectively between cathode contact 15 and heater contact 16 and the input terminals of a heater 19 mounted on the lower surface of cathode 3. While any suitable heater may be employed, the one illustrated is of the metalclad, insulated-type brazed to the lower surface of cathode 3 and which is disclosed and claimed in my copending application Ser. No. 811,067 (Docket RD-2352)tiled Mar. 27, 1969 and assigned to the assignee of this present invention.

In order to permit operation of the discharge device of my invention at high frequencies over a wide range of output powers and, consequently, high temperatures for the cathode and control grid, I provide temperature compensating supports for both the control grid and the cathode. The temperature compensating support for the control grid comprises a first corrugated metal ribbon 20 positioned between annulus 7 and grid contact ring 14. The temperature compensating support for cathode 3 comprises a second corrugated metal ribbon 21 connected between the outer edge of cathode 3 and the inner wall of the cylindrical cathode contact member 15. As illustrated, ribbon 21 rests on the shoulder 22 provided on the inner wall of cylindrical cathode contact member 15.

In selecting the materials for the temperature compensating support 20, a metal having a high coefficient of thermal conductivity is chosen so that heat generated in the control grid is rapidly conducted through bars 5 to annulus 7 and through corrugated ribbon 20 to grid contact member 14. For this purpose, annulus 7 and bars 5 may comprise a metal selected from the group consisting of molybdenum and tungsten. Metal contact ring 14 consisting of titanium and corrugated metal ribbon 20 comprises molybdenum.

Since it is desired to operate and maintain cathode 3 at a high temperature and to minimize loss of heat from the cathode, the material selected for second corrugated ribbon 21 is chosen to have a low coefficient of thermal conductivity. Typically, cathode 3 is formed of tungsten and cathode contact ring 15 is formed of titanium. Accordingly, to minimize loss of heat from cathode 3 to cathode contact ring 15, I form the second corrugated ribbon 21 of either tantalum or hafni- In the operation of an electron discharge device according to my construction at a high power output in the device, thermal expansion occurs in both the grid and cathode members. However, by use of corrugated supporting ribbon 20, the thermal expansion difference between the molybdenum or tungsten grid structure and the titanium contact ring is accommodated with no motion of the grid relative to the cathode. Similarly, by use of corrugated ribbon 21, thermal expansion of the cathode is accommodated without any longitudinal movement of the cathode. By use of the two temperature compensating supports, the relative motion between the grid and cathode surfaces are reduced to a minimum and thus the cathode and grid may be spaced closely and precisely to obtemperature and output power.

While I have shown and described several embodiments of my invention, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

I claim:

1. In an electron discharge device of the type having a planar anode, an opposed planar cathode and a planar grid positioned between the anode and the cathode, said grid comprising a metal annulus and a plurality of wires connected across the opening in said annulus, a temperaturecompensating support for said grid comprising a metal contact ring surrounding said annulus and having an inner wall in spaced-relationship with the outer wall of the annulus and a corrugated metal ribbon positioned between and in thermal contact with said walls, said ribbon comprising a metal having a high coeffi-- cient of thermal conductivity whereby heat generated in said grid wires and annulus during operation of said device is-transmitted from said annulus through said metal ribbon to said metal contact ring to prevent distortion and displacement of said grid.

2. In the device of claim 1 in which the annulus comprises a metal selected from the group consisting of molybdenum and tungsten and the metal of said contact ring comprises titanium, the corrugated metal ribbon comprises molybdenum.

3. In the device of claim 2, an annulus which consists of molybdenum.

4. in the device of claim 2, an annulus which consists of tungsten.

5. In the device of claim 1, a cathode comprising a circular metal member, a heater for said cathode, a cathode contact member encircling said cathode comprising a metal cylinder having an inner wall in spaced relation with the outer edge of said cathode member and a low thermal conductivity connection between said cathode and said contact member comprising a second corrugated metal ribbon positioned between and in thermal contact with the inner wall of said cylinder and the outer edge of said cathode member, said second ribbon comprising a metal having a low coefficient of thermal conductivity whereby heat loss from said cathode to said cathode contact member is minimized.

6. In the device of claim 5 in which said cathode member comprises molybdenum, said cathode contact member comprises titanium, and said second corrugated ribbon comprises tantalum or hafnium.

7. In the device of claim 5 in which said cathode member comprises tungsten, said cathode contact member comprises titanium, and said second corrugatedribbon' comprises tantalum or hafnium.

8. ln the device of claim 6, said second corrugated ribbon comprises tantalum.

9. In the device of claim 7, said second corrugated ribbon comprises tantalum.

10. In the device of claim 2, a cathode comprising a circular metal member, a heater for said cathode, a cathode contact member encircling said cathode member comprising a metal cylinder having an inner wall in spaced relationship with the outer edge of said cathode member, and a low thermal conductivity connection between said cathode and said contact member comprising a second corrugated metal ribbon positioned between and in thermal contact with the inner wall of said cylinder and the outer edge of said cathode member, said second ribbon comprising a metal having a low coefficient of thermal conductivitywhereby heat loss from said cathode to said cathode contact member is minimized.

11. In the device of claim 10, said cathode member comprises molybdenum, said cathode contact member comprises titanium, and said second corrugated ribbon comprises a metal selected from the group-consisting of tantalum or hafnil2. In the device of claim 11, said cathode member comprises tungsten, said cathode contact member comprises titanium, and said second corrugated ribbon comprises a metal selected from the group consisting of tantalum or hafnium.

13. In the device of claim 2, said corrugated metal ribbon is brazed to said annulus by a metal selected from the group consisting of gold and copper and is brazed to said metal contact member by an alloy selected from the group consisting of nickel-titanium and copper-titanium.

14. In an electron discharge device having a pair of spaced opposed planar electrodes, a temperature compensating support for one of said electrodes comprising a cylindrical member surrounding and in spaced relation with said one electrode and a corrugated metal ribbon positioned between and fastened to the outer edge of said electrode and in the inner wall of said cylindrical member, whereby lateral expansion of said electrode during high temperature operation of the device is absorbed by said ribbon without distorting or displaying said electrode.

Claims

1. In an electron discharge device of the type having a planar anode, an opposed planar cathode and a planar grid positioned between the anode and the cathode, said grid comprising a metal annulus and a plurality of wires connected across the opening in said annulus, a temperature compensating support for said grid comprising a metal contact ring surrounding said annulus and having an inner wall in spaced relationship with the outer wall of the annulus and a corrugated metal ribbon positioned between and in thermal contact with said walls, said ribbon comprising a metal having a high coefficient of thermal conductivity whereby heat generated in said grid wires and annulus during operation of said device is transmitted from said annulus through said metal ribbon to said metal contact ring to prevent distortion and displacement of said grid.

3. In the device of claim 2, an annulus which consists of molybdenum.

4. In the device of claim 2, an annulus which consists of tungsten.

7. In the device of claim 5 in which said cathode member comprises tungsten, said cathode contact member comprises titanium, and said second corrugated ribbon comprises tantalum or hafnium.

8. In the device of claim 6, sAid second corrugated ribbon comprises tantalum.

9. In the device of claim 7, said second corrugated ribbon comprises tantalum.

10. In the device of claim 2, a cathode comprising a circular metal member, a heater for said cathode, a cathode contact member encircling said cathode member comprising a metal cylinder having an inner wall in spaced relationship with the outer edge of said cathode member, and a low thermal conductivity connection between said cathode and said contact member comprising a second corrugated metal ribbon positioned between and in thermal contact with the inner wall of said cylinder and the outer edge of said cathode member, said second ribbon comprising a metal having a low coefficient of thermal conductivity whereby heat loss from said cathode to said cathode contact member is minimized.

11. In the device of claim 10, said cathode member comprises molybdenum, said cathode contact member comprises titanium, and said second corrugated ribbon comprises a metal selected from the group consisting of tantalum or hafnium.

12. In the device of claim 11, said cathode member comprises tungsten, said cathode contact member comprises titanium, and said second corrugated ribbon comprises a metal selected from the group consisting of tantalum or hafnium.