US3185881A - Cathode mount and lead-in structure for electron tubes - Google Patents

Description

May 25, 1965 A. s. woLFsoN CATHODE MOUNT AND LEAD-IN STRUCTURE FOR ELECTRON TUBES 2 Sheets-Sheet 1 Original Filed Sept. l0, 1958 ANTHONY S. WOLFSON INV EN l OR.

ATTORNEY May 25, 1965 A. s. woLFsoN 3,185,881

CATHODE MOUNT AND LEAD-IN STRUCTURE FOR ELECTRON TUBES 2 Sheets-Sheet 2 Original Filed Sept. l0, 1958 ANTHONY S. WOLF-'SON INVENTOR.

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ATTORNEY United States Patent O l 3,185,881 CATHODE MOUNT AND LEAD-IN STRUCTURE FOR ELECTRON TUBES Anthony S. Wolfson, Sunnyvale, Calif., assignor to Eitel- McCullough, Inc., San Carlos, Calif., a corporation of California 1 Continuation of application Ser. No. 760,205, Sept. 10, 1958. This application July 27, 1961, Ser. No. 127,401 17 Claims. (Cl. 313-82) This application is a continuation of application Serial No. 760,205 led September l0, 1958.

This invention relates generally to an electron gun and more particularly to .an electron gun for use in beam tubes of the type which deliver relatively high output power.

In tubes of this character, the electron gun must deliver an electron beam having a high electron current. A cathode having a large emitting surface is dictated. In general, larger cathodes include indirectly heated emitting surfaces. With larger emitting surfaces, to provide more electrons, satisfactory support of the heater elements becomes increasingly dicult.

As higher power electron gunsare constructed, the cooling problem are increased. If forced air or liquid cooling is employed, the liquid or gas employed must come in heat transfer contact with a large portion of the electron gun surface area to provide adequate cooling.

A further problem encountered in high power electron guns is one of arranging the parts so that a relatively high voltage may be applied between the elements without the occurrence of arcs between the elements.

' It is a general object of the present invention to provide an improved electron gun.

It is another object of the present invention to provide an electron gun which can be efficiently cooled.

It is another object of the present invention to provide an electron gun in which the complete assembly is carried on a metal base.

It is another object of the present invention to provide an electron gun which includes an improved heater assembly.

It is another object of the present invention to provide an electron gun which can be operated with relatively high voltages between the elements.

These and other objects of the invention will become more clearly apparent from the following description when taken in conjunction with the accompanying drawing.

Referring to the drawing:

FIGURE 1 is an elevational View, partly in section, of the lower part of a beam tube including an electron gun in accordance with the invention;

FIGURE 2 is a vertical half-sectional View showing an electron gun in accordance with the invention; y

FIGURE 3 is a bottom view of the electron gun of FIGURE 2;

FIGURE 4 is a plan view of the heater, looking down into the cathode assembly with the cathode disk removed; and

FIGURE 5 is a view taken along the line 5-5 of FIG- URE 2.

Generally, a beam tube comprises an elongated envelope having an electron gun at one end of the envelope and a collector electrode at the other end. An electron beam is generated by the gun and passes through a drift tube which extends axially of the tube between the gun and the collector. In FIGURE 1, the gun portion 11 of a beam tube is illustrated. The end of the Patented May 25, 1965 ICC drift tube which also serves as the main anode of the gun 11 is shown at 12.

The electrony gun 11 illustrated includes an oxide coated cathode dish 13 which may be prepared for emission in a well known manner. The cathode dish 13 is indirectly heated by a lamentary heater 16 to be presently described in detail. A cylindrical focus electrode 17 surrounds the cathode dish 13 and shapes the electron beam. A modulating anode 18 serves to control the current in the electron beam and the main anode 12 serves to accommodate the beam whereby it is projected aX1ally of the drift tube to the collector (not shown).

The cathode-heater assembly is carried on a metal base plate 19. Thus, the cathode dish 13 is mounted 1n the upper end of a cylindrical cathode support 21 which has its lower end secured to the base plate 19 by the screws 22. A mounting member 23 secured to the base plate 19 receives the screws 22. A second cylindrical support 24 is mounted concentrically within the support 21 by means of the screws 22 and mounting member 23. The support 24 carries a plurality of heat shields designated generally by the reference numeral 26. The cylinder also carries at its upper end a cylindrical member 27 which surrounds the lilamentary heater 16. Thus, it is seen that the combination of the heat shields 26 and cylindrical members 21 and 27 form a double walled oven-like enclosure which with the lower surface of the dish 13 Vencloses the lamentary heater 16. Cylindrical members 21, 24 .and 27 are made of thin metal to reduce the conduction of heat from such enclosures to the base plate 19.

The ilamentary heater 16 may be a four-section heater, as illustrated particularly in FIGURE 4. Each of the sections is supported at its two ends by posts which extend upwardly from the base plate 19. Thus, four central posts 31, are provided, one of which engages the inner end of each heater section 32 and four outer posts 33, are provided, one of which engages the outer end. Each of the sections comprises an elongated filament bent into a zig-zag shape having straight portions 28 and bight portions 29. The straight portions increase in length to form sector-shaped sections. As `shown in FIGURES 2 and 5, thecentral posts 31 are in direct electrical contact with the base plate 19. A pair of the outside posts 33 is supported on a ring 36, while another pair of outside posts is supported on an axially spaced ring 37. The rings 36 and 37 aresupported on and are insulated one from the other, and from the base plate 19 by the insulating spacer sleeves 38 associated with'the screws 39. Leads 40 and 41 (FIGURE 5) are secured to the rings 36 and 37, respectively. These leads are also connected to the lead-through posts 42 and 43, respectively. It is seen that the inner ends of the `heater sections 32 are shorted together by means of a metallic ring 30-which is carried by central posts 31. Thus, the sections 32 may be connected so that two ofthe sections are electrically in parallel with the other two sections or so `that all four sections are in parallel with each other to thereby accommodate different voltage sources for a given amount of heating.

The various sections 32 of the heater lament are fitted together like the pieces of a pie so that a circular heater structure is formed corresponding in size to cathode dish 13 and the emitting surface is uniformly heated. The 'zig-zag configuration of the lament provides low heater inductance. As shown, the heater may rbe dished to conform to the shape of the rear surface The base plate 19 also carries ceramic cylinders 46 and 47. The ceramic cylinders are preferably of high refractory material such as alumina and are metallized at both ends by suitable metallizing procedures such as by molybdenum manganese powder sintering.

The lower end of the cylinder 46 is suitably sealed to the base plate 19 by a sealing assembly designated generally by the reference numeral 4S. The sealing assembly includes a metal ring 49 which has one end suitably brazed to the base 19, and its other end extending upwardly. A second ring 51 has one end brazed to the ceramic cylinder 46, and its other end suitably heliarc welded to the other end of ring 49. A ceramic backing ring 52 is provided to add strength to the seal.

A lead-in ring 53 provides means for supporting and making electrical connection to the focusing electrode 17. The ring 53 is suitably brazed between the ceramic cylinders 46 and 47. The inner periphery of the ring S3 serves to support the focusing electrode 17, previously described. The electrode 17 may be attached thereto by means of spaced screws 54, for example.

The upper end of the ceramic cylinder 47 carries the modulating anode 18. A terminal ring 55 for making connection to the anode is provided and includes seal assemblies S6 and 5'7. The seal assembly 56 includes a sealing ring S which is brazed to the upper end of the cylindrical envelope portion 47 and has its other end suitably heliarc welded to the sealing ring 59. The ring 59 is suitably sealed to the terminal ring 5S, and backing ring 60 serves to strengthen the seal. The assembly 57 is similar to the one just described in that it includes sealing rings 61 and 62 with the sealing ring 61 having one end secured to the terminal ring S5, and its other end heliarc welded to the ring 62. The other end of the ring 62 is suitably brazed to the ceramic cylinder 63 which extends upwardly and supports the main anode 12. A ceramic backing ring 64 is provided, but as shown best in FlG- URE 2, an auxiliary ceramic backing ring 64' is interposed between backing ring 64 and terminal ring 55, so that the ceramic backing rings abut each other, and each abuts an associated envelope section.

The modulating anode 18 is suitably brazed to the ring 55. The anode is constructed with a rounded recessed portion 66 adjacent to the upper end of focusing electrode 17 The upper end of the focusing electrode 17 is rounded as shown at 67. The opposed surfaces of the anode and focusing electrode present rounded curved surfaces to one another to reduce the likelihood of arcing.

The base plate 19 carries mounting lugs '71 which may be brazed thereto. Lead-through terminals, previously referred to, are provided for making electrical connection to the posts 33 previously described. These connections may be of the type indicated in FIGURE 2 which include a lead-through post 42. Sealing rings 76 and 77 have one end sandwiched between and brazed to the ceramic ring 7 8 and the ceramic backing rings 49 and 3l., respectively. The other end of the ring '76 is suitably secured to the base plate 19, as for example, by brazing. The other end of the ring 77 is suitably secured to a flange 82 on the post 42, as for example, by brazing. Thus a vacuum-tight lead-through is provided.

The outer surface of the electron gun is relatively smooth to provide for intimate contact with a cooling medium. The bottom surface which supports the cathode may be efciently cooled by oil or by directing air over the same. The filamentary heater is enclosed within an oven-like enclosure and is a multi-section heater to provide low heater induction and even heating of the cathode surface whereby large heaters may be provided for relatively large cathode dishes. Improved heater supv port is provided and the gun is adapted for high voltage a cathode assembly including an indirectly heated cathode dish supported on said base plate, a pair of ceramic cylinders carried by said base plate, a focusing electrode supported on said base plate and surrounding said cathode, an anode carried by the upper end of the upper cylinder, and a plurality of heater sections positioned adjacent said dish, each of said sections being sector-shaped to uniformly radiate the entire dish.

2. An electron gun comprising a metallic base plate, a cathode assembly supported on said base plate, said assembly including a dish-shaped emitter, a plurality of heater sections comprising elongated ilamentary material zig-zagged to have straight portions and bight portions with the straight portions increasing in length to form a sector-shaped section, said plurality .of heater sections being mounted to cooperate with one another to uniformly radiate the entire emitter, a pair of stacked ceramic cylinders carried by said base, a focusing electrode carried by said base plate and surrounding the upper portion of said cathode assembly, and an anode carried adjacent the upper end of the upper cylinder.

3. An electron gun comprising a metallic base plate, a cathode assembly supported on said base, said assembly including a dish-shaped emitter, a plurality of heater sections mounted to indirectly heat said emitter, each of said sections comprising elongated iilamentary material zigzagged to form straight portions and bight portions with the straight portions having lengths such that a sectorshaped section is dened, said plurality of sections being mounted to cooperate with one another to uniformly radiate the entire emitter, a pair of ceramic cylinders carried by said base, a focusing electrode carried by said base plate and surrounding the upper portion of said cathode assembly, and an apertured anode carried adjacent the upper end of the upper ceramic cylinder, said anode including an annular recessed portion surrounding said aperture and facing an upper rounded end of the focusing electrode.

4. An electron gun comprising a flat metallic base plate, a cathode assembly supported on said base, said assembly including an indirectly heated dish-shaped emitter surface and a plurality of heater sections disposed to heat said emitter, each of said sections being sector-shaped whereby they may be mounted in cooperative relationship to uniformly radiate the entire emitter, a pair of stacked ceramic cylinders carried by said base, a focusing electrode carried by said base plate and surrounding the upper portion of said cathode assembly, and an apertured anode carried adjacent the upper end of the upper ceramic cylinder, said anode including an annular recessed portion surrounding said aperture and facing the upper end of the focusing electrode.

5. An Ielectron gun comprising a metal ibase, a cylindrical cathode support mounted on said base and extending upwardly, a dish-shaped cathode emitter carried by the upper end of the support cylinder, a plurality of iilament sections mounted to indirectly heat the underneath surface of the emitter, each of said heater sections comprising elongated lilamentary material formed to have straight portions and bight portions with the straight portions increasing in length to form a sector-shaped filament section whereby the plurality of sections may be mounted in cooperative relationship to uniformly radiate the entire under surface of the emitter, inner filament sup- |port posts directly mounted on said lbase and extending upwardly to engage one end of the ilamentary material forming a lament sec-tion, outer -iilament support posts mounted on the base and extending upwardly, each serving to engage the other end of the lamentary material forming a filament section, an inner cylinderextend-ing upwardly and concentric with the emitter support cylinder, a plurality of radiation shields carried yby said inner cylinder near the upper end of the same Vand serving to form an oven-like enclosure surrounding `said heater sections, a pair of spaced ceramic cylinders mounted on said base and extending upwardly, a cylindrical focusing electrode carried by said lbase plate and surrounding the cathode, and anode supported adjacent the upper end of the upper ceramic cylinder.`

6. An indirectly heated cathode assembly comprising a dish-shaped cathode emitter, a plurality of heater sections mounted to indirectly heat the emitter dish, each of the sections of said heater comprising elongated filamentary material formed to have straight portions and bight portions Iwith said straight portions having different lengths to form sector-shaped filament sections whereby the sections may be mounted in cooperative relationship to uniformly heat the entire under surface of the emitter dish.

7. An indirectly heated cathode assembly comprising a metal base, a dish-shaped cathode emitter, a plurality of heater sections mounted to indirectly heat the emitter dish, each of said sections comprising elongated material -formed to have straight por-tions and bight portions with said straight portions increasing in length to form sectorshaped filament sections whereby the sections may be mounted in cooperative relationship to uniformly radiate the ent-ire surface of the emitter dish, inner heater support post-s directly mounted on said base and extending upwardly, each of said posts serving to engage one end of the lamentary material of each 4filament; section, and a plurality of outer heater support posts mounted on the base and insulated therefrom and extending upwardly, each of said posts lserving to engage the other end of the filamentary Amaterial forming a heater section.

`8. An indirectly heated cathode comprising a metal base, a cylindrical cathode support mounted on said base and extending upwardly, a dish-shaped cathode emitter carried by the upper end of the support cylinder, a plurality of filament sections mounted to indirectly heat the underneath surface of the emitter, each of said heater sections comprising elongated filamentary material formed to have straight portions and bight portions with the straight portionsy having lengths such that a sector-shaped filament section is formed whereby the plurality of sections may be mounted in cooperative relationship to uniformly radiate the entire under surface of the emitter, inner filament support posts directly mounted on said base and extending upwardly to engage one end of the filamentary material forming a filament section, outer filament support posts mounted on the base and extendmg upwardly, each serving to engage the other end of the filamentary material lforming a filament section, an inner cylinderextending upwardly and concentric with the emitter support cylinder, and a plurality of radiation shields carried by said inner cylinder near the upper end of the same and serving to form `an oven-like enclosure surrounding said heater sections.

9. An indirectly heated cathode assembly comprising a metal base, a dish-shaped cathode emitter, a plurality of sector-shaped heater sections mounted to indirectly heat the emitterrdish, said sections being adapted to be mounted in cooperative relationship to uniformly radiate the entire lower surface of the emitter dish, inner heater support posts directly mounted on said base and extending upwardly, each of saidk posts serving to engage one end of one of the heater sections, a plurality of outer heater posts mounted on the base extending upwardly and insulated therefrom, each of said posts serving to engage the other end of one of the heater sections, at least one leadthrough connection for making electrical connection through .the base to selected ones of the outer heater posts, said lead-through including a conductive lead-through post extending through an enlarged opening Iformed in the metal base, and a metal-ceramic sealing assembly serving to support the lead-through post on the base and insulated therefrom.

10. In an electron tube having an evacuated envelope,

a seal assembly hermetically interconnecting two relatively movable adjacent envelope sections, said seal assembly comprising a metallic sealing yring structure having a first portion hermetioally united to one of said envelope sections, a second portion hermetically united to the other adjacent envelope sec-tion, and at least two mutually abutting backing ring members of dielectric material interposed between said envelope sections.

11. The combination according to claim 10, in which said iirst portion of the seal ring structure includes an annular flange having one peripheral edge portion hermetically united to the associated envelope section, said second portion of the seal ring structure includes an annular flange having one peripheral edge portion hermetically united to the other associated envelope section, and said backing ring members are interposed between the annular flange united to one of said envelope sections and the other adjacent envelope section.

l2. The combination according to claim 10, in which said first portion of the seal ring structure includes a cylindrical fiange radially spaced from the associated envelope section, and said second portion of the seal ring structure includes a cylindrical flange hermetically united to the lcylindrical flange of the first portion of the seal ring structure.

13. In an electron tube having `an evacuated envelope, -a metallic envelope wall member and a ceramic envelope Wall member adjacent each other, a metallic sealing ring structure forming a hermetically sealed bridge across the ladjacent portions of said envelope -wall members, said sealing ring structure having one end brazed to said metallic wall member and its other end brazed to said ceramic wall member, and ceramic structure means positioned in compression between said envelope wall members to form a ceramic-to-ceramic abutment bridged across by said sealing ring structure.

14. A vacuum tight lead-through assembly comprising an apertured metal plate, a metal electrical conductor extending through said aperture and having a radial fiange thereon spaced lfrom one side of said plate, dielectric ring means surrounding said conductor kand extending from said plate to said flange to support compressive loads therebetween, a first metal sealing ring bonded at one end to said plate and at its other end to said dielectric ring means, and a second metal sealing ring bonded at one end to said flange and at its other end to said dielectric ring means at a location on `the ring means spaced from said other end of the first metal ring, each of said fi-r-st and second metal rings having a free flexure portion intermediate its bonded ends.

15. A vacuum tight lead-through assembly comprising an apertured metal plate, a metal electrical conductor extending through said aperture and having a radial tiange thereon spaced .from one side of said plate, a first dielectric ring surrounding said conductor, a first metal sealing ring bonded at one end to said plate and at its other end to the end surface at one end of said first dielectric ring,

a second metal sealing ring bonded at one end to said flange and at its other end to the end surface at the other end of said first dielectric ring, each of said first and second metal rings having a free flexure portion intermediate its bonded ends, and two additional dielectric rings aligned with said first dielectric ring and positioned on opposite sides thereof in contact respectively with the end portions of said first and secondmetal rings which are bonded to the ends of the rst dielectric ring, said additional dielectric rings being also in abutment respectively with said plate and said flange.

l6. The combination according .to claim l5 in which said first -metal sealing rings surrounds the outer periphery of one of said additional dielectric rings and said second metal sealing ringfsurrounds the outer periphery of the other of said additional dielectric rings.

17. The `combination according to claim 15 in which said additional dielectric rings are bonded respectively to y PI d the end portions of said first and second metal rings on he side of said end portions opposite the side on which said end portions are bonded to said first dielectric ring.

References Cited by the Examiner UNITED STATES PATENTS 2,147,418 2/39 Bahls 174-5056 GEORGE N. WESTBY, Prmay Examiner.

RALPH G. NLSON, Examiner.

Claims (1)

1. AN ELECTRON GUN COMPRISING A FLAT METALLIC BASE PLATE, A CATHODE ASSEMBLY INCLUDING AN INDIRECTLY HEATED CATHODE DISH SUPPORTED ON SAID BASE PLATE, A PAIR OF CERAMIC CYLINDERS CARRIED BY SAID BASE PLATE, A FOCUSING ELECTRODE SUPPORTED ON SAID BASE PLATE AND SURROUNDING SAID CATHODE, AN ANODE CARRIED BY THE UPPER END OF THE UPPER CYLINDER,

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