US3090884A

US3090884A - Electron gun

Info

Publication number: US3090884A
Application number: US13020A
Authority: US
Inventors: George C Morse
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1960-03-07
Filing date: 1960-03-07
Publication date: 1963-05-21
Anticipated expiration: 1980-05-21

Description

y 21, 1963 s. c. MORSE 3,090,884

ELECTRON GUN Filed March 7, 1960 INVENTOR. GEORGE C. MORSE BY 2 K fizz/@244 ATTORNEYS United States Patent C 3,090,884 ELEQTRGN GUN George C. Morse, Woodside, Calif, assignor to Eitel McCullough, inc, San Bruno, Calii, a corporation of California Filed Mar. 7, 196b, Ser. No. 13,92li 6 Claims. (Cl. 3l3256) The invention relates to electron guns, and particularly to a ruggedized electron gun.

One of the objects of the invention is the provision of an electron gun in which the electrode structure is integrally united as by brazing to the envelope.

Another object of the invention is the provision of an electron gun construction in which the portion of the tube envelope enclosing the electron gun forms an end cap for the tube and rigidly supports the electron gun elements.

A still further object of the invention is the provision of an electron gun in which the parts may be integrally united into a composite assembly in one operation.

A still further object of the invention is the provision of an electron gun in which the electrode elements are protected against, and are unaffected by, vibration and impact shocks.

The invention possesses other objects and features of advantage, some of which, with the foregoing will be set forth in the following description of the invention. It is to be understood that the invention is not limited to the embodiment disclosed, as variant embodiments may be adopted within the scope of the appended claims.

Broadly considered, the invention comprises an electron gun in which a portion of the evacuated envelope is utilized to enclose and rigidly support the electron gun elements. Thus, a cylindrical wall portion is integrally and hermetically united to a support plate portion to form an end cap for the evacuated envelope. Supported within the end cap thus formed is an electron emitting assembly including cathode and heater, both of which are integrally united to the end cap. Also enclosed and rigidly supported on and within the end cap is a focusing electrode.

Means are provided on the support plate for orienting and integrally uniting the support plate to each element of the electron emitting assembly and focusing electrode. Apertures in the end cap provide access to the interior of the envelope for terminal leads connected at their innor ends to selected electron gun elements and at their outer ends forming terminal leads outside the envelope. At its end remote from the support plate, the cylindrical wall portion is integrally and hermetically united to an accelerating anode. The accelerating anode is cooperatively interposed between the gun assembly and the radiofrequency structure to which the electron gun is secured.

Referring to the drawings: FIGURE 1 is a vertical half sectional view.

FIGURE 2 is a plan View of the support plate taken in the direction indicated by the arrows on the line 22 in FIGURE 1.

FiGURE 3 is a bottom plan view taken in the direction indicated by the arrow 3 in FIGURE 1.

FIGURE 1 is drawn to a scale approximately twice ac tual size, and FIGURES 2 and 3 are drawn approximately actual size.

In greater detail, the electron gun is adapted to be integrally and hermetically attached as the end portion or cap or" an evacuated envelope generally designated by the numeral 2, and only a portion of which is shown for purposes of description. The electron gun comprises a cylindrical wall portion 3, preferably formed of dielectric material such as alumina, across one metalized end of which is integrally and hermetically brazed a support plate 4, also preferably formed of dielectric material. The cylindrical dielectric wall portion 3 is metalized across its opposite end surfaces in a manner well known in the art, while the dielectric support plate 4 is provided with a plurality of metalized surface areas 6, 7 and 8. As shown best in FIGURE 2, the peripheral metalized surface area 8 is a continuous circular area, while the metalized surface areas 6 and 7 are arcuate, each terminating at points spaced on opposite sides of an associated aperture. Apertures 9 and 12 are related respectively, with metalized surface areas 6 and 7, and cooperate with these metalized areas in a manner to be hereafter described. Aperture 13, lying within the unmetalized surface area defined by the arcuate metalized surface area 6, extends through the support plate, as do apertures 9 and 12, and on the opposite side of the support plate each of the apertures is surrounded by a metalized surface area 14, shown best in FIGURE 3. Also shown best in FIG- URE 3, is the peripheral metalized surface area '16 similar to the metalized area 8 but on the opposite side of the support plate.

Concentrically arranged within the cylindrical wall portion 3 and supported on the plate 4, is an electron emitting assembly designated generally by the numeral 1'7, and including a cathode 18 adapted to be heated by a heating coil 19. The cathode-heater assembly is supported on a hollow metallic shell structure 21, which at its outer end 22 is provided with a flange 23 integrally brazed to the arcuate metalized surface area 6. As shown in FIGURE 1, the hollow metallic shell 21 conveniently comprises an upper generally cylindrical portion 24 having apertures 26 therein, and a lower hollow conical section 27. While the upper cylindrical portion and the lower conical section have been shown as two separate parts having their adjacent overlapping ends integrally brazed as at 28, it will be apparent that shell structure 21 may be fabricated from a single piece. It will thus be seen that the hollow metallic shell 21, :brazcd at its broad end 22 to the metalized surface area 6 on the support plate, provides a very rigid construction adapted to support the cathode and heater assembly in a manner preventing movement of these elements by vibration or shock. Ad ditionally, the hollow metallic shell 21 provides a convenient means of conducting electrical energy between the heater coil and its source of supply. Also, the hollow shell 2%, fabricated preferably from thin gauge material, provides a convenient means of preventing the conduction of heat away from the cathode. This function is further aided by the provision of a hollow cylindrical shell 29 of Kovar, integrally interposed between the upper end portion of tubular shell 24 and the cathode. This shell functions as a heat dam to prevent the flow of heat away from the cathode.

Concentrically arranged within the hollow heat dam 29 are a plurality of superimposed radiating heat shields St). The heat shields are of a material and shape to radiate heat from the heater coil back toward the cathode, thus increasing the efiiciency of the electron gun. To support the heat shields in spaced superimposed relation, each of the heat shields is provided with a dimple 31 struck from the material of the shield and extending downwardly to abut the upper surface of the next lower heat shield. The assembly of heat shields is rigidly retained in position below the heater coil by a supporting battle plate 32, having a peripheral flange 33 integrally welded to the inner surface of the hollow heat dam shell 29.

Dielectric bushings 34, extending through apertures in the heat shields and supporting bafile plate 32, provide means for passage of electrical leads 36 connecting the ends of heater coil 19. One end of the heater coil lead 36 accuses extends through a bushing 34 and is brazed at its outer end to one end of a strip conductor 37, which is in turn brazed at its other end to the inner surface of flange 33. The other end of heater lead 36 is integrally brazed within one end of tube 38, which extends outwardly through aperture '13. On its end exterior to the support plate 4, the tube 38 is provided with a terminal cap 39, closed at its outer end 4 1, and having a radially extending flange 42 at its opposite end. The flange 42 is integrally and hermetica'lly brazed to the annular metalized surface area 14 surrounding the aperture 13. A metal plug 43 within the terminal cap is integrally brazed to the exterior end of the tube 38 and to the interior surfaces of the cap to provide an electrically conductive path for the terminal lead 36. It will thus be seen that the terminal cap provides an hermetic seal about the aperture 13, and also functions to provide 'a convenient electrical connection to a source of power. Such connection may conveniently be made by spring clips (not shown) arranged to resiliently. engage the terminal cap. A similar construction, shown in elevation in FIGURE 1, serves to electrically connect the other end of the heater coil to ground. in this case the inner end of tube 38 terminates at and is brazed to the flange 23 on the conical shell portion 27, thus making an electrical connection through the supporting shell 21. If desired, the flange 23 may be apertured to receive the end of the tube, which would then also aid in orienting the shell on the associated metalized area. To strengthen the hermetic union between the flanges 42 and the associated metalized surface areas 14, a backing cylinder 44 of ceramic is provided about the terminal cap 39. The cylinder of ceramic 44 is brazed at one end to the opposite side of the flanges 42 from the support plate. Stresses on opposite sides of the flanges are thus equalized and a long life is assured for the hermetic seal at this point.

Concentrically enclosed within the cylindrical dielectric wall portion 3 is a second hollow metallic shell 46. This shell includes the focusing electrode for the electron gun, and comprises an upper tubular portion 47, having an indentation 48 intermediate its ends, and a lower conical section 49 having an outwardly extending flange 51 at its lower end integrally brazed to the arcuate metalized surface area 7 on the support plate 4. At its free inner end the focusing electrode is provided with a rolled-over edge '2, providing a smooth contour to prevent the formation of an arc between the focusing electrode and the surrounding elements of the electron gun. As with the hollow metallic shell 21, the focusing electrode shell 46 is shown to be fabricated in two

pieces

47 and 49 integrally joined at overlap 53. It is apparent that instead of being fabricated in two pieces the shell 46 may be fabricated in a single unit. The indentation 48 in the focusing electrode cooperates with the cathode to converge the electron beam in the desired degree and direction. Alternately, instead of being an indentation in the material of the shell itself, a short hollow cylinder (not shown) may be brazed within the upper portion 47 of the shell in place of the indentation to effect the same purpose.

'It will thus be seen that when the shell 46 is integrally brazed to the arcuate metalized surface area 7 on the support plate 4-, the broad base of the shell cooperates by the integral nature of its union with the supporting plate to provide a rigid and vibration-free construction. It will also. be apparent that the parts are adapted to be fabricated in composite units such as focusing electrode and electron emitting assembly, and the units then arranged within the cylindrical dielectric portion 3 on the plate 4 and the units oven-brazed in a single operation. To connect the focus electrode -46 to a source of energy, a terminal cap 39 as previously described, is brazed on the metalized surface area 14 associated with the aperture 12. A lead (not shown) extending from the terminal cap 39 through the aperture 12, is integrally brazed at its inner end to the flange 51 and forms a conductive path for energy from a source not shown. To support the electron gun in an appropriate socket, a cylindrical metallic flange 54 is provided integrally brazed to the annular surface area 16 on the bottom side of the support plate 4. A measure of resilience is provided in the flange by dividing the flange into circumferentially spaced segments by means of vertical slots 55.

integrally united to the inner end of the cylindrical dielectric Wall portion 3, is an accelerating electrodeor anode assembly 56. The accelerating anode comprises a radially extending annular web 57, having a portion 58 of reduced thickness adjacent its outer peripheryinterposed between web 57 and terminal ring 59, and an annular recess 65 positioned opposite the rolled edge 5-2 of the focusing electrode 46. The accelerating anode lies in axially spaced relation to the focusing electrode 46 and the electron emitting assembly, and is integrally and hermetically brazed adjacent its outer periphery to the associated end of the cylindrical dielectric wall portion 3. A short drift tube section 61 is integrally brazed Within the inner periphcry of the web 57.

To hermetically unite the accelerating anode to the end of the cylinder 3, a cylindrical flange 62 is provided with a radially extending integral annular flange 63, brazed adjacent its inner periphery to the metalized end of dielectric cylinder 3. The cylindrical flange 62 lies snugly within a cylindrical sleeve 6d integrally and hermetically brazed at one end to the peripheral terminal ring portion 59 of the accelerating anode 56, and at its other end 65 integrally and hermetically heliarc welded to the cylindrical flange 62. An integral and hermetic union is thus formed between the accelerating anode and the end of the cylinder 3 which may be subsequently opened to permit removal of the gun for repairs. As with the flanges 42 on terminal caps 39, a short cylindrical ceramic section 66 is brazed to the opposite side of the flange 63 in axial alignment with dielectric cylinder 3. Ceramic section 66 equalizes the stresses imposed on flange 63 by expansion and contraction of the parts due to extremes in temperature. The free end of the ceramic section 66 slidably abuts the inner surface of the accelerating anode portion 58. The other side of the accelerating anode 56 is integrally and hermetically sealed in like manner to the adjacent end of the envelope 2. As shown, a flange 67 brazed at one end across the end of the envelope portion 2, cooperates with a second flange 68 brazed at one end to the accelerating anode 56. Heliarc welding the flanges 67 and 68, as at the edge 69, hermetically seals the union of the two flanges at this point, while providing a joint which may be sub sequently opened.

From theforegoing it will be apparent that a rugged and economically manufacturable gun construction has been provided. The cylindrical and conical cross sections of the parts render them inherently strong, and the integral interconnection as by brazing and welding renders them unaffected by vibration and shock.

I claim:

1. In an electron gun for an electron tube having an evacuated envelope, the combination comprising an apertured dielectric support plate forming a portion of the envelope wall, a plurality of metalized surface areas arranged on at least one side of said dielectric plate, and an electron emitting assembly including a cathode having a concave emitting surface supported on said dielectric plate and integrally brazed to a selected one of said metalized surface areas.

2. The combination according to claim :1, in which a focus electrode is provided supported on said dielectric support plate and is integrally brazed to a second one of said metalized surface areas.

3. The combination according to claim 1, in which a hollow cylindrical dielectric wall portion open at-both ends is provided supported on said dielectric support plate and extending about said electron emitting assembly, one end of said cylindrical dielectric wall portion being brazed to a third one of said metalized surface areas.

4. The combination according to claim 3, in which an accelerating anode is integrally and hermetically brazed on the end of said cylindrical dielectric wall portion remote from said dielectric support plate.

5. In an electron beam tube having an evacuated envelope, the combination comprising an end cap constituting a portion of the envelope wall and including a hollow dielectric cylindrical Wall portion open at one end and a dielectric support plate portion closing the other end thereof, an electron emitting assembly mounted on said support plate, a focus electrode mounted on said support plate and operatively associated with the emitting assembly to focus electrons into a beam, and an aperture/d anode hermetically sealed to the open end of said end cap in operative relation to said emitting assembly to effect projection of a beam of electrons through the open end of the end cap.

6. The combination according to claim 5, in which the mounting of said emitting assembly and focus electrode on the support plate comprises two spaced arcuate metalizing layers on the inner surface of said support plate, a tubular metallic support shell for said emitting assembly, a tubular metallic support shell for said focus electrode, the base of each of said shells having a radially extending flange seated on one of said metalizing layers, and a metallic bond joining each of said flanges to its respective metalizing layer.

References Cited in the file of this patent UNITED STATES PATENTS 2,883,575 Wilson Apr. 21, 1959 2,910,607 McCullough Oct. 27, 1959 2,956,192 Heil Oct. 11, 1960

Claims

5. IN AN ELECTRON BEAM TUBE HAVING AN EVACUATED ENVELOPE, THE COMBINATION COMPRISING AN END CAP CONSTITUTING A PORTION OF THE ENVELOPE WALL AND INCLUDING A HOLLOW DIELECTRIC CYLINDRICAL WALL PORTION OPEN AT ONE END AND A DIELECTRIC SUPPORT PLATE PORTION CLOSING THE OTHER END THEREOF, AN ELECTRON EMITTING ASSEMBLY MOUNTED ON SAID SUPPORT PLATE, A FOCUS ELECTRODE MOUNTED ON SAID SUPPORT PLATE AND OPERATIVELY ASSOCIATED WITH THE EMITTING ASSEMBLY TO FOCUS ELECTRONS INTO A BEAM, AND AN APERTURED ANODE HERMETICALLY SEALED TO THE OPEN END OF SAID END CAP IN OPERATIVE RELATION TO SAID EMITTING ASSEMBLY TO EFFECT PROJECTION OF A BEAM OF ELECTRONS THROUGH THE OPEN END OF THE END CAP.