US3195003A

US3195003A - Electron discharge device

Info

Publication number: US3195003A
Application number: US238229A
Authority: US
Inventors: Jagt Anton Van Der
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1962-11-16
Filing date: 1962-11-16
Publication date: 1965-07-13
Anticipated expiration: 1982-07-13
Also published as: GB1032208A

Description

United States Patent 3,195,003 ELECTRON DESCHARGE DEVHCE Ante-n van der .lagt, Wheeler Township, Steuben County, N.Y., assigrror to Westinghouse Eiectric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Nov. 16, 1962, er. No. 238,229 Ciaims. (Cl. 313-337) The present invention relates to electron discharge devices and more particularly to electron emissive cathodes of the thermionic type for use in electron discharge devices.

it is known in the art of thermionic cathodes for electron discharge devices that the rate of electron emission for a given material is primarily dependent upon two factors: namely, the area and the temperature of the emissive surface. The most common form of indirectly heated emissive cathode comprises a long sleeve or tubular member of suitable cross-sectional configuration having a heating element disposed Within the tubular member. An electron emissive coating is placed on the outside of the tubular member. This type of cathode provides a large emissive area and is also efiicient in that, as the heater is in very close proximity to the emissive surface, the heat transfer to the tubular member is good. Also, as the openings in the ends of the tubular members are small and relatively distant with respect to the majority of the length of the heater, only small amounts of the heat produced by the heater are lost through these openings. Also, the heat losses due to conduction to the support members (usually mica-s), cathode tab and heater legs are small when compared to the total heat capacity of the heater.

While cathodes of the above-described nature have proven generally satisfactory for a great number of devices, they do suffer from certain defects. Among these defects is the fact that the long cathode is particularly susceptible to microphonic noises due to actual physical vibration and, therefore, the support of the cathode within an electron discharge device can present some serious problems. Also, the long cathode structure necess'itates a correspondingly long device which may be undesirable in certain circumstances.

These deficiencies in the so-called long cathode may be overcome through the use of 'a shorter cathode having a larger cross sectional area. However, prior attempts at a short cathode have largely been unsatisfactory in that due to the relatively large open ends of the tubular section and the relatively short distance from these open ends to most parts of the heater, radiation losses have been extremely high. Also, the thermal conduction losses to the support members increases rapidly with the increase in tube diameter. While it is true that, even including these losses, the cathode may be brought to the proper temperature by increasing the heater wattage and hence the temperature of the heater, this results in a lowering of the overall efiiciency of the device. Increased heater temperature may also be extremely detrimental to the heater itself as, by virtue of the higher temperature, the heater will have a greatly shortened life. It is, therefore, an object of this invention to provide an improved electron discharge device.

Another object is to provide an improved thermionic electron emissive cathode.

A further object is to provide a thermionic cathode of high efficiency.

Another object is to provide a thermionic cathode in which the ratio of length to width is small.

A still further object is to provide an electron emissive cathode of high electron emission and low heater temperature.

Stated briefly, the present 'inve'ntion'describes an electron discharge device employing a double wall cathode structure of short length and large cross sectional area. The double wall structure is preferably comprised of two -tubular members of different cross sectional areas which are coaxially aligned and which have the spacing between the two -m'er'nbers at one end thereof closed off. A cathode shield, which is common in many electron discharge devices, is positioned at the other end of the tubular members and serves to etfectively close oif that end of the tubes. The heater assembly for the device is located in the spacing between the two tubular members.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty 'which characterize the invention will be pointed out in particularity in the claims annexed to and forming a partof this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is an 'elevation'al view, partially broken away and partially in section of a discharge device embodying the cathode of the present invention in its preferred form; and I FIGS. 2 and 3 are modifications of the cathode of FIG.'1 in accordance with the present invention.

With reference to FIG. 1, there is shown a discharge device incorporating the invention in its preferred form. The device includes anenvelope '10 which is closed at one end and is provided with a tipped-off exhaust tube 12. The other end of the envelope 10 is closed off with a button stem header 14. 'Disposed within the envelope 1% is an electrode cage assembly indicated generally at 16. The cage assembly includes an anode 18, a grid 20, and a cathode 22. The cage assembly is supported within 'the envelope by means of an insulating member 24, which is of a suitable material such as mica.

A plurality of pins 26 extend through the header 14. The pins 26 serve to support the member 24 within the envelope 16 and also serve as electrical leads for the electrodes of the cage assembly. Suitable members 28 connect the .pins 26 to the various electrodes of the cage assembly 16.

In FIG. 1, the cathode assembly 22 is shown in its preferred'embodiment. The cathode assembly 22 comprises an inner tubular member 30 and an outer tubular member 32. T he'tubular

members

30 and 32 are spaced rom each other and are, preferably, in the form of spaced concentric cylindrical tubes; although, it is obvious that configurations other than circular may be utilized. The inner tube Si) is preferably of a low heat conducting material such as Inconel, an International Nickel Company trademark for a high nickel-chromium alloy including about 79.5% nickel, 13% chromium, 6.5% iron, and lesser amounts of manganese, silicon, carbon and copper. The outer tube 32 is made of a suitable material such as nickel. The

tubular members

30 and 32 are maintained in a spaced relationship with the. outer member being supported by the inner member through the utilization of a washer or apertured'disk 36 which is positioned between thetwo

members

30 and 32 at their upper edge. The disk 36 is retained in position by welding it to the inner member'3l) and outer member 32 along itsinnerand outer peripheries to form a unitary structure. It is seen that the washer 36 not only spaces the two tubular members 30 and 3 2, but also acts as ameans for supporting the outer member 32 from the inner tubular member 30. The washer 36 also closes olf the end space between the two

tubular members

30 and 32 and prevents, in this area, the loss 'of heat through radiation from the heater. The washer 36 is preferably made of a good heat conducting material, for example, nickel. Thus, it is seen that a good heat conducting path is provided between the inner tube 30 araaoos and the outer tube 32, in order to raise the temperature of the outer tube 32.

A heater assembly 33 is positoned within the space between the two tubular members 3% and 32 to provide for the heating of the cathode. The heater is generally or" standard construction and includes a length of wire having an insulating coating on the outside thereof. In FIG. 1, the heater 38 is shown in the form of a coil which extends throghout the space between the two

tubular elemeans

30 and 32. A suitable electron emissive coating 34, which may be any or those known in the art, is placed on the outside surface of the outer tubular member 32 to provide for electron emission upon the heating of the cathode.

A substantially disk-shaped support 24, of suitable material such as mica, glass or ceramic, is provided at the opposite end of the tubular members from the washer 36.

lsshown in FIG. 1, the shield 24 contains a centrally located aperture 46 having a diameter equal to that of the inside diameter of the inner tube 3%). The inner tube 39 may be provided at its lower end with a radially extending shield 44 which abuts against the 'upper surface of the support'zd. The shield 44 may be made integrally with the inner tube 30.

The cathode assembly 22 is connected to the support 24 by means of a rivet member 42 having a head 43 and a body portion 41. The body portion 41 is of such size so as to provide a compression or force fit within the inside of the tubular member 30 with the head 43 of the rivet 42 hearing against the lower surface of the support 24. The rivet member 42 is preferably made of a poor heat conducting material such as lnconel so as to provide a poor heat conducting path to the support 24 and thereby minimize heat loss. a

As shown in FIG. 1, the outer tube 32 is slightly shorter in length than the inner tube 3! Thus, it is readily seen that while the inner tube 30 contacts the shield 44, the outer tubular member 32 does not but is instead positioned slightly apart therefrom. Thus, no direct conductive path is provided in this area for the removal of heat from the outer tube 32. The distance between lower edge 33 of the outer tube 32 to the top surface of the shield 44 is somewhat critical. If this distance is too large, heat will be lost from the spacing between the tubular members by radiation. If the space is too small, heat will be lost through radiation-conduction. .In practice, it has been found that a distance of from about to about mils produces good results.

In FIG. 2 and 3 there are shown modifications of the cathode structure of FIG. 1 in accordance with the present invention. FIG. 2 differs from FIG. 1 primarily in that the washer 36 of FIG. 1 has been omitted and in its place has been substituted a flange portion 50. The flange portion 59 is formed integrally with the inner tube and extends radially outwardly therefrom such that it is in contact with the outer tube 32. The flange portion 56 and the outer tube 32 are then welded together at their peripheral junction 51 to provide the requisite support for the outer tube 32 and the closure between the two tubular members. Also in FIG. 2, the means of securing the inner tube 30 to the shield 44 has been changed. In this case, the shield 44 is afiixed to the inner tube 30 through the use of a peripheral braze 54 on the upper surface of the shield 44. Also, it is noted that instead of the coil heater as in FIG. 1, an expanded spade wound heater 37 has been utilized in this embodiment.

FIG. 3 differs from FIG. 2 in that an inwardly extending flange 56 is provided at the top portion of the outer tubular member 32. This flange 56 extends radially inward and is in'contact with the inner tube 30. Again as in FIG. 2 a peripheral weld is made at the top edge of the tubes to provide the necessary closure and requisite support. The inner tube 30 may be brazed to the cathode shield 44. A heater 39 of FIG. 3 is shown as an unfolded coil heater.

It is evident that any of the heaters shown, or any suit able heater, may be used in any of the embodiments and that the heater is provided with leads extending through one or more holes within the member 24 to provide the necessary power for the-heater.

In the preferred embodiment, the cathode is made with a ratio of overall length to overall diameter of less than 2:1. This presents a more thickset cathode than is prevalent in the art. Thus, by the relatively large diameter and the means'for the prevention of heat loss, the cathode thus described is less susceptible to microphonics and is one of high efficiency. The high efficiency primarily results from the construction of the cathode assembly which reduces, the radiation and conduction losses by incorporating, in the cathode design, heat shields and poor heat con- 'duction paths. Also, by the above-described construction, it has been found that the temperature gradient along the cathode surface is very small. Thus, the emission qualities of the cathode of the present design are very'good.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. For example, one possible modification would utilize the support member 24 as the cathode heat shield. It is not desired, therefore, that the invention be limited to the specific arrangement shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. An electron discharge device comprising an electrode cage assembly including a thermionic cathode for the emission of electrons, said cathode comprising a first tubular member, a second tubular member, said first and second tubular members maintained in a substantially concentric relation .to form a space between said tubular members, heater means disposed within said space said first tubular member b eing'made of a material having a higher heat conductivity than that of said second tubular member, and means extending between said tubular members at one end thereof said means being made of a high heat conductive material to form an efiicient heat conducting path from said second tubular member to said first tubular member.

2. An electron discharge device comprising an electrode cage assembly including an electron emissive thermionic cathode, said. cathode comprising inner and outer tubular members, said outer tubular members being made of a material having a higher heat conductivity than the material of "said inner tubular member, said outer member being positioned around and spaced from said inner member, a heater disposed Within the spacing betweensaid tubular members, an electron emissive coating on the outer surface of said outer member, means at one end of said tubular members for closing off the space between said members, said means formed as an annular'disc interposed between said tubular members andmade of a highly heat conductive material to establish a heat conducting path from said inner tubular member to said outer tubular member, 'and shield means disposed at the opposite end of said members and extending in a direction transverse to the axis thereof, said shield means being secured to said inner member and being spaced with respect to the end of said outer member.

3. An electron discharge device comprising an electrode cage asesmbly including an electron emissive thermionic cathode comprising inner and outer spaced, hollow cylindrical members, said members being coaxial and substantially coextensive, said outer cylindrical member being made of a higher heat conductivematerial than the material of said inner cylindrical'member, an electron emissive coating on the outer surface of said outer me. ber, heater means disposed between said members, disc means atone end of said cylindrical members for closing off the space therebetween, said means having a radial dimension substantially smaller than the axial dimensions of said cylindrical members and being made of a highly heat conductive material to establish a heat conducting path from said inner cylindrical member to said outer cylindrical member, and shield means disposed in a plane substantially perpendicular to .the axis of said cylindrical members at the other end thereof, said shield means extending across the spacing between said cylindrical members and being secured to said inner member and closely spaced from the end of said outer member.

4. In an electron discharge device, an electron em-issive thermionic cathode comprising inner and outer spaced, hollow cylindrical members, said outer cylindrical member being made of a higher heat conductive material than the material of said inner cylindrical member, said members being coaxial and substantially coextensive, an electron emissive coating on the outer surface of said outer member, heater means disposed between said members, means at one 'end of said cylindrical members for closing off the space therebetween, said means being formed of an annular disc member having a radial dimension substantially smaller than the axial length of said cylindrical members and being made of nickel to establish an efi'icient heat path from said inner cylindrical member to said outer cylindrical member, and shield means disposed in a plane substantially perpendicular to the axis of said cylindrical member at the other end thereof, said shield means extending across the spacing between said cylindrical members and being secured to said inner member and closely spaced from the end of :said outer member, said spacing being in the range of from about 10 to 20 mils.

5. A thermionic cathode for the emission of electrons comprising a first tubular member of relatively poor heat conduction material, a second tubular member of relatively good heat conduct-ion material positioned about and spaced from said first tubular member, heater means disposed within the space between said tubular members, means extending between said tubular members at one end thereof whereby the space between said tubular members is closed oif, and shield means disposed at the other end of said tubular members, said shield means extending in a direction transverse to the length of said tubular members and positioned in a closely spaced relationship with respect to the end of said second tubular member.

References Qited by the Examiner UNITED STATES PATENTS 1,955,537 4/34 Davies 3l3339 2,650,997 9/53 Watfous 3l338 2,813,227 11/57 Sweet 31326O FOREIGN PATENTS 1,151,321 8/57 France.

DAVID J. GALVIN, Primary Examiner.

Claims

2. AN ELECTRON DISCHARGE DEVICE COMPRISING AN ELECTRODE CAGE ASSEMBLY INCLUDING AN ELECTRON EMISSIVE THERMIONIC CATHODE, SAID CATHODE COMPRISING INNER AND OUTER TUBULAR MEMBERS, SAID OUTER TUBULAR MEMBERS BEING MADE OF A MATERIAL HAVING A HIGHER HEAT CONDUCTIVITY THAN THE MATERIAL OF SAID INNER TUBULAR MEMBER, SAID OUTER MEMBER BEING POSITIONED AROUND AND SPACED FROM SAID INNER MEMBER, A HEATED DISPOSED WITHIN THE SPACING BETWEEN SAID TUBULAR MEMBERS, AN ELECTRON COATING ON THE OUTER SURFACE OF SAID OUTER MEMBER, MEANS AT ONE END OF SAID TUBULAR MEMBERS FOR CLOSING OFF THE SPACE BETWEEN SAID MEMBERS, SAID MEANS FORMED AS AN ANNULAR DISC INTERPOSED BETWEEN SAID TUBULAR MEMBERS AND MADE A HIGHLY HEAT CONDUCTIVE MATERIAL TO ESTABLISH A HEAT CONDUCTING PATH FROM SAID INER TUBULAR MEMBER TO SAID OUTER TUBULAR MEMBER, AND SHIELD MEANS DISPOSED AT THE OPPOSITE END OF SAID MEMBERS AND EXTENDING IN A DIRECTION TRANSVERSE TO THE AXIS THEREOF, SAID SHIELD MEANS BEING SECURED TO SAID INNER MEMBER AND BEING SPACED WITH RESPECT TO THE END OF SAID OUTER MEMBER.