GRIDDED ELECTRON TUBE EMPLOYING COOLED CERAMIC INSULATOR FOR MOUNTING CONTROL GRID
United States Patent 3809939
The gridded gun of an electron tube includes an annular high voltage beryllia insulator body having good thermal conductivity. The thermionic cathode emitter is mounted within the central bore in the annular beryllia insulator in thermally insulative relation relative to the insulator body. The control grid and focus electrode for the gun are mounted from the surface of the annular insulator facing the anode. The outer periphery of the annular insulator is mounted to the body of the electron tube in heat exchanging relation therewith, such that the control grid is cooled by thermal conduction through the beryllia insulator body to the cooled main body of the electron tube.
US Patent References:
/3706002.html
Miram et al. - December 1972 - 3706002
Fluid coolant system for a plasma-jet generator
Perugini - June 1968 - 3390292
DEPRESSABLE BEAM COLLECTOR STRUCTURE FOR ELECTRON TUBES
Jackson - May 1972 - 3666980
/3706002.html
Miram et al. - December 1972 - 3706002
Fluid coolant system for a plasma-jet generator
Perugini - June 1968 - 3390292
DEPRESSABLE BEAM COLLECTOR STRUCTURE FOR ELECTRON TUBES
Jackson - May 1972 - 3666980
Inventors:
Miram, George V. (Daly City, CA)
Mizuhara, Yosuke M. (San Francisco, CA)
Mizuhara, Yosuke M. (San Francisco, CA)
Application Number:
05/304703
Publication Date:
05/07/1974
Filing Date:
11/08/1972
View Patent Images:
Export Citation:
Assignee:
Varian Associates (Palo Alto, CA)
Primary Class:
Other Classes:
313/23, 313/46, 313/289
International Classes:
H01J23/065; H01J23/02; H01J1/02
Field of Search:
313/19,23,28,39,46,256,258,289
Primary Examiner:
Lawrence, James W.
Assistant Examiner:
Punter, Wm H.
Attorney, Agent or Firm:
Cole, Stanley Aine Harry Stoddard Robert Z. E. K.
Claims:
1. In an electron tube:
2. The apparatus of claim 1 wherein said annular insulator body includes an annularly corrugated surface facing said anode means to define first and second annular lands separated by a first annular groove, and said control grid means and said focus electrode means being mounted to said first and
3. The apparatus of claim 2 wherein said annular beryllia insulator body includes a second annular groove in said surface facing said anode to define a third annular land, and wherein said mounting means for mounting said beryllia insulator to said cooled body portion of said evacuable
4. The apparatus of claim 1 wherein said mounting means includes a thin yieldable metallic tubular portion bonded via a gas tight seal at one end
5. The apparatus of claim 2 wherein the top portions of said first and second lands of said insulator body lie in substantially the same plane
6. The apparatus of claim 3 wherein the top portions of said first, second and third lands of said insulator body lie substantially in the same plane
7. The apparatus of claim 1 wherein said control grid means includes a concave grid portion extending across said beam path and an annular radially directed lip portion, said lip portion being bonded to said insulator body in heat exchanging relation therewith for conduction
8. The apparatus of claim 1 including heat shield means interposed between said cathode emitter means and the wall of said bore in said insulator body for thermally insulating said cathode emitter from said beryllia insulator.
2. The apparatus of claim 1 wherein said annular insulator body includes an annularly corrugated surface facing said anode means to define first and second annular lands separated by a first annular groove, and said control grid means and said focus electrode means being mounted to said first and
3. The apparatus of claim 2 wherein said annular beryllia insulator body includes a second annular groove in said surface facing said anode to define a third annular land, and wherein said mounting means for mounting said beryllia insulator to said cooled body portion of said evacuable
4. The apparatus of claim 1 wherein said mounting means includes a thin yieldable metallic tubular portion bonded via a gas tight seal at one end
5. The apparatus of claim 2 wherein the top portions of said first and second lands of said insulator body lie in substantially the same plane
6. The apparatus of claim 3 wherein the top portions of said first, second and third lands of said insulator body lie substantially in the same plane
7. The apparatus of claim 1 wherein said control grid means includes a concave grid portion extending across said beam path and an annular radially directed lip portion, said lip portion being bonded to said insulator body in heat exchanging relation therewith for conduction
8. The apparatus of claim 1 including heat shield means interposed between said cathode emitter means and the wall of said bore in said insulator body for thermally insulating said cathode emitter from said beryllia insulator.
Description:
BACKGROUND OF THE INVENTION
Heretofore, gridded electron guns for klystron tubes and the like have employed an annular high voltage insulator body of alumina or beryllia ceramic with the thermionic cathode emitter being coaxially disposed of the annular insulator body. The control grid and the focus electrode were mounted to the beryllia ceramic body, whereas the cathode emitter was mounted in thermally insulative relation relative to the control grid and relative to the beryllia insulator body. However, both the focus and control grid structures as well as the cathode emitter were mounted well above the surface of the insulator body facing the anode such that a relatively long thermal path was provided between the control grid and the insulator body. This resulted in relatively poor cooling of the control grid through the insulator body to the body of the tube.
Cooling of the prior control grid was achieved by placing a fluid coolant in heat exchanging relation with the grid support structure and high voltage insulator body to affect cooling of the control grid. Such a prior art tube is disclosed and claimed in copending U.S. Pat. No. 3,706,002 issued Dec. 12, 1972 and assigned to the same assignee as the present invention.
While fluid cooling of the control grid support structure and high voltage insulator assembly results in sufficient cooling for the control grid to prevent unwanted thermionic emission from the control grid when the tube is supposedly turned off, it results in an undue complication of the electron gun assembly. More particularly, the electron gun assembly must include means for containin the fluid coolant or for flowing the coolant through the electron gun in heat exchanging relation with the grid support structure. In addition, it causes the electron gun assembly to be longer than normal due to the added length caused by the coolant chamber and the baffle structure for directing the coolant through the electron gun assembly.
Cooling of the control grid of the electron gun is extremely important for if the grid is not sufficiently cooled it will serve as a thermionic cathode emitter when the grid is pulsed negative relative to the cathode for turning off the tube. This unwanted grid emission can produce interpulse noise which is highly undesirable in high power pulsed klystron tubes. In a typical example, the cathode emitter may be operating at 800° C, whereas the control grid should preferably be operated at a temperature not in excess of 200° C. The control grid may be disposed only 0.039 inches from the hot cathode emitter. Thus very ample cooling for the grid must be provided in order to maintain at least a 600° C differential between the closely spaced control grid and the thermionic cathode emitter. The problem is even further complicated when the electron gun assembly is encased in a silicone rubber potting material for improved electrical insulation at reduced atmospheric pressure, as encountered at high altitudes for airborne applications. The silicone rubber utilized as the potting material has very poor thermal conductive properties, thereby rendering external cooling of the electron gun extremely difficult.
SUMMARY OF THE PRESENT INVENTION
The principal object of the present invention is the provision of an electron tube having improved control grid cooling.
In one feature of the present invention, the electron gun includes an annular cathode-to-anode high voltage insulator body of beryllia ceramic with the cathode emitter mounted within the central bore of the insulator in thermally insulative relation and with the control grid mounted across the central bore of the insulator in thermally conductive relation and the insulator body, in turn, mounted in thermally conductive relation to the body of the electron tube, whereby the control grid is cooled via thermal conduction through the high voltage insulator to the cooled body of the tube.
In another feature of the present invention, the annular beryllia ceramic cathode-to-anode insulator body has an annularly corrugated surface facing the anode to define a plurality of radially separated land portions with the control grid being bonded to the innermost annular land portion of the insulator body.
In another feature of the present invention, the surface of the annular beryllia ceramic cathode-to-anode insulator includes first and second annular land portions facing the anode with the control grid affixed to the first annular land and the focus electrode mounted to the second land.
Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic longitudinal sectional view of a klystron tube incorporating features of the present invention,
FIG. 2 is an enlarged detail sectional view of a portion of the structure of FIG. 1 delineated by line 2--2, and
FIG. 3 is a detail view of a portion of the structure of FIG. 2 delineated by line 3--3 and depicting an alternative embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1 there is shown a microwave high power klystron tube 1 incorporating features of the present invention. The klystron tube includes an electron gun assembly 2 for forming and projecting a beam of electrons 3 over an elongated beam path to a beam collector structure 4 disposed at the terminal end of the elongated linear beam 3. A plurality of cavity resonators 5 are successively arranged along the beam path for successive electromagnetic interaction with the electron beam passable therethrough.
Microwave energy to be amplified is applied to the upstream cavity 5' via an input coupling means, such an input coupling loop 6. The microwave energy in the input cavity 5' velocity modulates the beam 3. The velocity modulated beam excites successive floating cavity resonator 5 disposed along the beam path to produce current density modulation of the beam at the gap of the output resonator 5". The current density modulated beam at the output gap excites the output resonator 5" and output microwave energy is extracted from the output resonator 5" via a suitable output coupling means, such as output coupling loop 7, which couples the energy to a suitable load, such as an antenna, not shown.
A solenoid 8 or permanent magnet structure, schematically represented by solenoid 8, is disposed around the tube for producing an axially directed beam focusing magnetic field throughout the length of the beam path from the gun to the collector 4 for focusing the beam through the structures disposed along the beam path.
In the electron gun 2, a negative potential, as of -10 kV, is applied to the cathode emitter 10 from a beam power supply 9. The control grid 11 overlays the cathode emitter 10 for controlling the beam current. The control grid 11 is bias negative relative to the cathode 10 by a relatively small dc bias potential as of a few hundred volts, supplied by potential supply 12. The control grid 11 is pulsed positive relative to the cathode 10 for turning on the beam by a pulse pwoer supply 13, thereby pulsing the beam current. A relatively small power supply 14, as of 7 volts, is connected across the heater leads of a heating element 15 for heating the cathode 10 to thermionic emission temperature, as of 800° C.
The body of the tube 1 is preferably operated at ground potential which is also anode potential Va and is provided with means for cooling the body of the tube and keeping its temperature at approximately 65° to 76° C, in use. In a typical example, the body of the tube 1 is made of copper and is cooled by means of fluid coolant passageways (tubes) 16 disposed in heat exchanging relation with the body of the tube 1. Fluid coolant such as water is directed through the coolant tubes 16 for removing heat from the body of the tube.
Referring now to FIG. 2, there is shown the electron gun assembly 2 incorporating features of the present invention. More particularly, the gun includes a centrally apertured anode plate 17 forming a portion of and operating at the potential of the body of the tube 1, namely ground potential. The electron gun 2 includes an annular anode-to-cathode insulator body 18 of beryllia ceramic. The thermionic cathode emitter 10 is mounted within the central bore 19 of the insulator body 18 in thermally insulative relation relative to the insulator body 18.
The insulator body 18 is joined to the anode portion 17 of the body of the tube 1 via the intermediary of an annular metallic sealing member 21, as of copper. More particularly, sealing member 21 includes a relatively thin wall tubular portion 22, as of 0.025 thick, sealed as by brazing to the adjacent surface of the insulator 18 at 23 to provide a thermally conductive joint at 23 between the sealing member 21 and the insulator 18. The tubular portion 22 of the sealing member 21 is made relatively thin to allow for unequal radial thermal expansion between the insulator body 18 and sealing member 21 without producing excessive strain on the relatively brittle insulator 18. The other end of the sealing member 21 may be brazed to the copper anode 17 to provide a good thermally conductive joint between the sealing member 21 and the body of the tube. As an alternative, the sealing member 21 merely abutts the anode 17 and is sealed to the anode 17 and main body of the tube 1 via a pair of radially directed sealing rings 24 and 25 which are brazed at their inner ends to the sealing member 21 and anode 17, respectively, and are sealed together at their outer periphery, as by heliarc welding, at 26 to provide a vacuum tight joint between the electron gun 2 and the anode 17. Atmospheric presusre on the outside of the electron gun 2 pushes the sealing member 21 into good thermal contact with the anode 17.
The surface of the annular high voltage insulator 18 which faces the anode 17 is provided with first and second annular grooves 27 and 28 defining first, second and third annular land portions 29, 31 and 32. The control grid 11 includes a multiapertured spherically concave central portion 32 and a radially directed outer lip portion 33. The lip portion 33 is brazed at its outer periphery to the top of the first land 29 to provide a thermally conductive joint between the control grid 11 and the thermally conductive insulator 18.
A beam focus ring 34, as of stainless steel, is disposed intermediate the control grid 11 and anode 17 for focusing the electron beam through a constricted central aperture 35 of the anode 17. The focus ring 34 is mounted to the second annular land 31 via a sealing ring 36, as of kovar, and an annular ceramic backup ring 37, as of beryllia ceramic, is sealed to the opposite side of the ring 36 from that of the land 31 to equalize the thermal stress on the sealing ring 36. The annular grooves 27 and 28 serve to increase the electrical leakage path along the surface of the insulator 18 to permit high voltages to be applied between electrodes without producing electrical breakdown across the surface of the insulator 18.
A control grid lead 38 passes through an axially directed bore 39 in insulator 18 and is connected to the lip 33 of the control grid 11 for applying the operating potential thereto. Likewise, a focus electrode lead 41 passes axially through a bore 42 in the insulator 18 and is connected at one end to the focus electrode support ring 36 for applying the focus electrode potential to focus ring 34. In a preferred embodiment, the focus ring 34 is operated at cathode potential and thus, the other end of focus lead 41 is connected to the metallic cathode support structure at 43.
The thermionic cathode emitter 10, in a preferred embodiment, comprises nickel oxide coated cathode consisting of a spherically concave nickel base member having its concave face preferably dimpled with a multiplicity of spherically concave dimples of lesser radius of curvature arranged in a closely packed geometry and coated with a cathode emissive material in the conventional manner. The heating element 15 is disposed adjacent the backside of the cathode emitter button and serves to heat the cathode emitter 10 to operating temperature, as of 800° C. The cathode emitter button is carried at its periphery in a hollow tubular member 44, as of molybdenum. A plurality of heat shielding partitions 45 are sealed across the tubular member 44 for retaining the heat within the immediate region of the cathode emitter 10. A second hollow cylindrical heat shield 46 surrounds the cathode emitter support 44 to minimize loss of heat by radiation to the surrounding ceramic insulator 18. Shield 46 is spaced from the inner wall 19 of the insulator to minimize transfer of thermal energy from the cathode assembly to the surrounding cathode-to-anode insulator 18.
The cathode support tube 44 includes an outwardly flared base portion 47 which is sealed as by brazing to an inner mounting ring 48. Mounting ring 48 includes a shoulder 49 which abutts a similar mating shoulder on an outer mounting ring 51 which is carried from the high voltage insulator 18 via the intermediary of a kovar sealing ring 52 brazed to the outer mounting ring 51 and to the insulator 18 at 53. The mating shoulder on the outer mounting ring 51 is machined accurately with respect to the top of the land 29 such that when the shoulder 49 of the inner mounting ring 48 is pressed into axial engagement therewith the emitting surface of the cathode emitter is accurately positioned relative to the position of the control grid 11 which is carried from the top of the first land 29. The mounting rings 48 and 51 are laser welded together at 54 to fixedly secure the cathode and heater assembly within the insulator 18.
The electron gun assembly 2 is closed at the bottom end via an end closing disc 55 as of alumina ceramic, which is mounted to the first sealing ring 52 via a mating sealing ring 56, as of kovar, brazed to the closing plate 55. The mating sealing rings 52 and 56 are outwardly flanged at 57 and sealed in a vacuum tight manner by means of a helium arc weld running about the periphery of the mating flanges 57. Gas tight electrical feedthroughs 58 and 59 make connection through the end plate 55 to one of the heater leads 61 and to the control grid lead 38, respectively. The other end of the heater element is connected to cathode potential which is applied to the tube via the mating flanged portion 57. The electron gun is encased with an electrically insulative potting compound 63. A suitable potting compound is silicone rubber.
In a typical example of an X-band multi-cavity klystron amplifier, the anode-to-cathode insulator 18 has an outer diameter of 2 inches and an axial length of 0.5 inches. The inside diameter of the central bore 19 at its narrowest point is approximately 0.6 inches and the spacing between the anode-to-cathode insulator 18 and the anode 17 is approximately 0.347 inches. The cathode emitter 10 operates at approximately 800° C and the control grid 11 operates at a temperature of approximately 200° C at its center and 150° C at its outer periphery, whereas the body of the tube operates at approximately 75° to 65° C. The focus electrode 34 operates at approximately 100° C. Thus, ample cooling is obtained for the control grid 11 via the thermal conduction achieved through the beryllia anode-to-cathode insulator 18 and mounting ring 21 to the body of the tube 1.
A particular advantage of the anode-to-cathode insulator 18 of FIG. 2 is that the surface of the insulator 18 which faces the anode may be ground flat to facilitate obtaining precise positional referencing of the control grid 11 and focus ring 34 relative to the cathode emitter 10 and anode 17.
Referring now to FIG. 3 there is shown an alternative embodiment of the present invention. In this embodiment, the annular anode-to-cathode insulator body 18 includes an axially directed hollow cylindrical portion 68 which is joined to the body of the tube via a pair of concentric annular tubular leg portions 22 of the mounting ring member 21. The parallel legs 22 define a fluid coolant passageway 69 in the space between the legs 22 such that the fluid coolant may be brought into direct contact with the end of the insulator 68 to facilitate cooling of the anode-to-cathode insulator 18 and to allow higher anode-to-cathode voltage to be employed due to the increased axial length of the anode-to-cathode insulator body.
Heretofore, gridded electron guns for klystron tubes and the like have employed an annular high voltage insulator body of alumina or beryllia ceramic with the thermionic cathode emitter being coaxially disposed of the annular insulator body. The control grid and the focus electrode were mounted to the beryllia ceramic body, whereas the cathode emitter was mounted in thermally insulative relation relative to the control grid and relative to the beryllia insulator body. However, both the focus and control grid structures as well as the cathode emitter were mounted well above the surface of the insulator body facing the anode such that a relatively long thermal path was provided between the control grid and the insulator body. This resulted in relatively poor cooling of the control grid through the insulator body to the body of the tube.
Cooling of the prior control grid was achieved by placing a fluid coolant in heat exchanging relation with the grid support structure and high voltage insulator body to affect cooling of the control grid. Such a prior art tube is disclosed and claimed in copending U.S. Pat. No. 3,706,002 issued Dec. 12, 1972 and assigned to the same assignee as the present invention.
While fluid cooling of the control grid support structure and high voltage insulator assembly results in sufficient cooling for the control grid to prevent unwanted thermionic emission from the control grid when the tube is supposedly turned off, it results in an undue complication of the electron gun assembly. More particularly, the electron gun assembly must include means for containin the fluid coolant or for flowing the coolant through the electron gun in heat exchanging relation with the grid support structure. In addition, it causes the electron gun assembly to be longer than normal due to the added length caused by the coolant chamber and the baffle structure for directing the coolant through the electron gun assembly.
Cooling of the control grid of the electron gun is extremely important for if the grid is not sufficiently cooled it will serve as a thermionic cathode emitter when the grid is pulsed negative relative to the cathode for turning off the tube. This unwanted grid emission can produce interpulse noise which is highly undesirable in high power pulsed klystron tubes. In a typical example, the cathode emitter may be operating at 800° C, whereas the control grid should preferably be operated at a temperature not in excess of 200° C. The control grid may be disposed only 0.039 inches from the hot cathode emitter. Thus very ample cooling for the grid must be provided in order to maintain at least a 600° C differential between the closely spaced control grid and the thermionic cathode emitter. The problem is even further complicated when the electron gun assembly is encased in a silicone rubber potting material for improved electrical insulation at reduced atmospheric pressure, as encountered at high altitudes for airborne applications. The silicone rubber utilized as the potting material has very poor thermal conductive properties, thereby rendering external cooling of the electron gun extremely difficult.
SUMMARY OF THE PRESENT INVENTION
The principal object of the present invention is the provision of an electron tube having improved control grid cooling.
In one feature of the present invention, the electron gun includes an annular cathode-to-anode high voltage insulator body of beryllia ceramic with the cathode emitter mounted within the central bore of the insulator in thermally insulative relation and with the control grid mounted across the central bore of the insulator in thermally conductive relation and the insulator body, in turn, mounted in thermally conductive relation to the body of the electron tube, whereby the control grid is cooled via thermal conduction through the high voltage insulator to the cooled body of the tube.
In another feature of the present invention, the annular beryllia ceramic cathode-to-anode insulator body has an annularly corrugated surface facing the anode to define a plurality of radially separated land portions with the control grid being bonded to the innermost annular land portion of the insulator body.
In another feature of the present invention, the surface of the annular beryllia ceramic cathode-to-anode insulator includes first and second annular land portions facing the anode with the control grid affixed to the first annular land and the focus electrode mounted to the second land.
Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic longitudinal sectional view of a klystron tube incorporating features of the present invention,
FIG. 2 is an enlarged detail sectional view of a portion of the structure of FIG. 1 delineated by line 2--2, and
FIG. 3 is a detail view of a portion of the structure of FIG. 2 delineated by line 3--3 and depicting an alternative embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1 there is shown a microwave high power klystron tube 1 incorporating features of the present invention. The klystron tube includes an electron gun assembly 2 for forming and projecting a beam of electrons 3 over an elongated beam path to a beam collector structure 4 disposed at the terminal end of the elongated linear beam 3. A plurality of cavity resonators 5 are successively arranged along the beam path for successive electromagnetic interaction with the electron beam passable therethrough.
Microwave energy to be amplified is applied to the upstream cavity 5' via an input coupling means, such an input coupling loop 6. The microwave energy in the input cavity 5' velocity modulates the beam 3. The velocity modulated beam excites successive floating cavity resonator 5 disposed along the beam path to produce current density modulation of the beam at the gap of the output resonator 5". The current density modulated beam at the output gap excites the output resonator 5" and output microwave energy is extracted from the output resonator 5" via a suitable output coupling means, such as output coupling loop 7, which couples the energy to a suitable load, such as an antenna, not shown.
A solenoid 8 or permanent magnet structure, schematically represented by solenoid 8, is disposed around the tube for producing an axially directed beam focusing magnetic field throughout the length of the beam path from the gun to the collector 4 for focusing the beam through the structures disposed along the beam path.
In the electron gun 2, a negative potential, as of -10 kV, is applied to the cathode emitter 10 from a beam power supply 9. The control grid 11 overlays the cathode emitter 10 for controlling the beam current. The control grid 11 is bias negative relative to the cathode 10 by a relatively small dc bias potential as of a few hundred volts, supplied by potential supply 12. The control grid 11 is pulsed positive relative to the cathode 10 for turning on the beam by a pulse pwoer supply 13, thereby pulsing the beam current. A relatively small power supply 14, as of 7 volts, is connected across the heater leads of a heating element 15 for heating the cathode 10 to thermionic emission temperature, as of 800° C.
The body of the tube 1 is preferably operated at ground potential which is also anode potential Va and is provided with means for cooling the body of the tube and keeping its temperature at approximately 65° to 76° C, in use. In a typical example, the body of the tube 1 is made of copper and is cooled by means of fluid coolant passageways (tubes) 16 disposed in heat exchanging relation with the body of the tube 1. Fluid coolant such as water is directed through the coolant tubes 16 for removing heat from the body of the tube.
Referring now to FIG. 2, there is shown the electron gun assembly 2 incorporating features of the present invention. More particularly, the gun includes a centrally apertured anode plate 17 forming a portion of and operating at the potential of the body of the tube 1, namely ground potential. The electron gun 2 includes an annular anode-to-cathode insulator body 18 of beryllia ceramic. The thermionic cathode emitter 10 is mounted within the central bore 19 of the insulator body 18 in thermally insulative relation relative to the insulator body 18.
The insulator body 18 is joined to the anode portion 17 of the body of the tube 1 via the intermediary of an annular metallic sealing member 21, as of copper. More particularly, sealing member 21 includes a relatively thin wall tubular portion 22, as of 0.025 thick, sealed as by brazing to the adjacent surface of the insulator 18 at 23 to provide a thermally conductive joint at 23 between the sealing member 21 and the insulator 18. The tubular portion 22 of the sealing member 21 is made relatively thin to allow for unequal radial thermal expansion between the insulator body 18 and sealing member 21 without producing excessive strain on the relatively brittle insulator 18. The other end of the sealing member 21 may be brazed to the copper anode 17 to provide a good thermally conductive joint between the sealing member 21 and the body of the tube. As an alternative, the sealing member 21 merely abutts the anode 17 and is sealed to the anode 17 and main body of the tube 1 via a pair of radially directed sealing rings 24 and 25 which are brazed at their inner ends to the sealing member 21 and anode 17, respectively, and are sealed together at their outer periphery, as by heliarc welding, at 26 to provide a vacuum tight joint between the electron gun 2 and the anode 17. Atmospheric presusre on the outside of the electron gun 2 pushes the sealing member 21 into good thermal contact with the anode 17.
The surface of the annular high voltage insulator 18 which faces the anode 17 is provided with first and second annular grooves 27 and 28 defining first, second and third annular land portions 29, 31 and 32. The control grid 11 includes a multiapertured spherically concave central portion 32 and a radially directed outer lip portion 33. The lip portion 33 is brazed at its outer periphery to the top of the first land 29 to provide a thermally conductive joint between the control grid 11 and the thermally conductive insulator 18.
A beam focus ring 34, as of stainless steel, is disposed intermediate the control grid 11 and anode 17 for focusing the electron beam through a constricted central aperture 35 of the anode 17. The focus ring 34 is mounted to the second annular land 31 via a sealing ring 36, as of kovar, and an annular ceramic backup ring 37, as of beryllia ceramic, is sealed to the opposite side of the ring 36 from that of the land 31 to equalize the thermal stress on the sealing ring 36. The annular grooves 27 and 28 serve to increase the electrical leakage path along the surface of the insulator 18 to permit high voltages to be applied between electrodes without producing electrical breakdown across the surface of the insulator 18.
A control grid lead 38 passes through an axially directed bore 39 in insulator 18 and is connected to the lip 33 of the control grid 11 for applying the operating potential thereto. Likewise, a focus electrode lead 41 passes axially through a bore 42 in the insulator 18 and is connected at one end to the focus electrode support ring 36 for applying the focus electrode potential to focus ring 34. In a preferred embodiment, the focus ring 34 is operated at cathode potential and thus, the other end of focus lead 41 is connected to the metallic cathode support structure at 43.
The thermionic cathode emitter 10, in a preferred embodiment, comprises nickel oxide coated cathode consisting of a spherically concave nickel base member having its concave face preferably dimpled with a multiplicity of spherically concave dimples of lesser radius of curvature arranged in a closely packed geometry and coated with a cathode emissive material in the conventional manner. The heating element 15 is disposed adjacent the backside of the cathode emitter button and serves to heat the cathode emitter 10 to operating temperature, as of 800° C. The cathode emitter button is carried at its periphery in a hollow tubular member 44, as of molybdenum. A plurality of heat shielding partitions 45 are sealed across the tubular member 44 for retaining the heat within the immediate region of the cathode emitter 10. A second hollow cylindrical heat shield 46 surrounds the cathode emitter support 44 to minimize loss of heat by radiation to the surrounding ceramic insulator 18. Shield 46 is spaced from the inner wall 19 of the insulator to minimize transfer of thermal energy from the cathode assembly to the surrounding cathode-to-anode insulator 18.
The cathode support tube 44 includes an outwardly flared base portion 47 which is sealed as by brazing to an inner mounting ring 48. Mounting ring 48 includes a shoulder 49 which abutts a similar mating shoulder on an outer mounting ring 51 which is carried from the high voltage insulator 18 via the intermediary of a kovar sealing ring 52 brazed to the outer mounting ring 51 and to the insulator 18 at 53. The mating shoulder on the outer mounting ring 51 is machined accurately with respect to the top of the land 29 such that when the shoulder 49 of the inner mounting ring 48 is pressed into axial engagement therewith the emitting surface of the cathode emitter is accurately positioned relative to the position of the control grid 11 which is carried from the top of the first land 29. The mounting rings 48 and 51 are laser welded together at 54 to fixedly secure the cathode and heater assembly within the insulator 18.
The electron gun assembly 2 is closed at the bottom end via an end closing disc 55 as of alumina ceramic, which is mounted to the first sealing ring 52 via a mating sealing ring 56, as of kovar, brazed to the closing plate 55. The mating sealing rings 52 and 56 are outwardly flanged at 57 and sealed in a vacuum tight manner by means of a helium arc weld running about the periphery of the mating flanges 57. Gas tight electrical feedthroughs 58 and 59 make connection through the end plate 55 to one of the heater leads 61 and to the control grid lead 38, respectively. The other end of the heater element is connected to cathode potential which is applied to the tube via the mating flanged portion 57. The electron gun is encased with an electrically insulative potting compound 63. A suitable potting compound is silicone rubber.
In a typical example of an X-band multi-cavity klystron amplifier, the anode-to-cathode insulator 18 has an outer diameter of 2 inches and an axial length of 0.5 inches. The inside diameter of the central bore 19 at its narrowest point is approximately 0.6 inches and the spacing between the anode-to-cathode insulator 18 and the anode 17 is approximately 0.347 inches. The cathode emitter 10 operates at approximately 800° C and the control grid 11 operates at a temperature of approximately 200° C at its center and 150° C at its outer periphery, whereas the body of the tube operates at approximately 75° to 65° C. The focus electrode 34 operates at approximately 100° C. Thus, ample cooling is obtained for the control grid 11 via the thermal conduction achieved through the beryllia anode-to-cathode insulator 18 and mounting ring 21 to the body of the tube 1.
A particular advantage of the anode-to-cathode insulator 18 of FIG. 2 is that the surface of the insulator 18 which faces the anode may be ground flat to facilitate obtaining precise positional referencing of the control grid 11 and focus ring 34 relative to the cathode emitter 10 and anode 17.
Referring now to FIG. 3 there is shown an alternative embodiment of the present invention. In this embodiment, the annular anode-to-cathode insulator body 18 includes an axially directed hollow cylindrical portion 68 which is joined to the body of the tube via a pair of concentric annular tubular leg portions 22 of the mounting ring member 21. The parallel legs 22 define a fluid coolant passageway 69 in the space between the legs 22 such that the fluid coolant may be brought into direct contact with the end of the insulator 68 to facilitate cooling of the anode-to-cathode insulator 18 and to allow higher anode-to-cathode voltage to be employed due to the increased axial length of the anode-to-cathode insulator body.