US2984762A

US2984762A - Electron beam tube and magnetic circuitry therefor

Info

Publication number: US2984762A
Application number: US735630A
Authority: US
Inventors: Laird K S Haas
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1958-05-15
Filing date: 1958-05-15
Publication date: 1961-05-16
Anticipated expiration: 1978-05-16
Also published as: GB906274A; DE1293917B; NL239266A; FR1224509A; DE1291837B; DE1293911B; NL105112C

Description

y 6,1961 L. K. s. HAAS 2,984,762

ELECTRON BEAM TUBE AND MAGNETIC CIRCUITRY THEREFOR Filed May 15, 1958 3 Sheets-Sheet 1 INVENTOR. Laird K5. Haas A TTORNE y 1961 L. K. s. HAAS 2,984,762

ELECTRON BEAM TUBE AND MAGNETIC CIRCUITRY THEREFOR Filed May 15, 1958 3 Sheets-Sheet 2 INVENTOR. La/rd K5. Haas BY MFW ATTORNEY y 15, 1961 L. K. s. HAAS 2,984,762

ELECTRON BEAM TUBE AND MAGNETIC CIRCUI 'IRY THEREFOR Filed May 15, 1958 3 Sheets-Sheet I5 INVENTOR. Laird K5. Haas A TTU/Q/VE) Patented May' 16, 1961 fiice ELECTRON BEAM TUBE AND MAGNETIC ClRCUITRY THEREFOR Laird K. S. Haas, San Mateo, Calif., assiguor to Eitei- McCullough, Inc., San Bruno, Calif., a corporation of California Filed May 15, 1958, Ser. No. 735,630

12 Claims. (Cl. 315-35) This invention relates to beam type electron tubes and more particularly to traveling wave tubes.

The overall object of this invention is to provide a traveling wave tube which will operate at high altitudes and in very humid atmosphere, and at the same time have a reliable power output of more than one watt at the fundamental frequency over a frequency range of 4000 to 7000 megacycles, while having a minimum small signal gain of over 50 decibels. Further, the purpose is to provide a tube which will have these capabilities while operating in magnetic circuits of unusually low weight and power requirements.

More specifically, and in order to provide a tube having the mentioned capabilities, an object of the invention is to provide a novel tube construction which will permit use of a magnetic circuit of reduced radial dimen sions, thereby reducing hte weight and size of the magnetic circuit, regardless of whether a permanent magnet or magnetic coil is used. Briefly, this object is accomplished by extending the input and output couplings for the tube longitudinally out the ends of the tube rather than out the sides, combined with the innovation of a removable cooling structure. The combination of these two features permits the design of a very small diameter tube which can be inserted in a magnetic circuit having a very small inner diameter.

Another specific object is to provide an improved means for obtaining a coaxial line type of coupling in an electron tube, and more particularly for providing such a coupling through the electron gun of a traveling wave tube.

A further object of the invention is to provide an 7 improved arrangement for extending the output coupling of a traveling wave tube past the collector and out the end of the tube.

Another specific object of the invention is to provide an improved tube construction which will have more complete shielding from radio frequency leakage. This shielding is particularly important because the high gain of this tube accentuates the possibility of radio frequency leakage which could lead to instability of operation.

An additional specific object of the invention is to provide an improved tube construction in which the various terminals are sealed in plastic material so that arcing between the terminals will not occur even at high altitude or high humidity.

A further object is to provide improved magnetic circuitry for a traveling wave tube.

Another object is to provide an extremely rugged traveling wave tube and circuitry mounting therefor which will permit stable operation even under conditions of substantial vibration.

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 disclosed species, as variant embodiments thereof are contemplated and may be adopted within the scope of the claims.

Referring to the drawings:

Figure 1 is a longitudinal cross-section of a traveling wave tube according to the invention;

Figures 2 through 5 are cross-sectional views along the lines 22 through 5-5 in Figure 1; and

Figure 6 is a side view of the tube in its magnetic circuit, showing the tube in elevation and the magnetic circuit in cross-section.

Referring in more detail to Figure 1 and Figures 2-5, which are sections of Figure 1, the tube comprises an electron gun 10 for initiating an electron beam, an elongated envelope portion 11 through which the beam travels, and a collector 12 in which the beam terminates.

Gun 10 comprises a generally electrical envelope formed from a plurality of alternate ceramic rings 14 and metal members 1625. The ends of the ceramic rings are metalized by conventional metalizin-g procedure and are meta'llically bonded, as by brazing, to the annular sealing surface on the adjacent metal members. The metal members '17, 18, 19, 21 and 22 serve as electrode leads and are provided externally of the envelope with terminal tabs to which the lead wires 26-30 are soldered.

Internally the gun comprises a heater 33 which is electrically and mechanically connected to the metal members 17 and 18. A cathode 34 and shield 35 are connected to metal member 19. Metal member 20 supports a focus electrode 37, and metal member 22 extends inwardly to provide an apertured anode or accelerating electrode 38. A flash type getter 39 is connected between metal members 22 and 23. Metal member 25 extends inwardly to provide a second apertured anode or accelerating electrode 40. The electron gun thus described serves to initiate a beam of electrons directed through the envelope portion 11.

Inside the envelope portion 11 means are provided for radio frequency interaction with the beam generated by gun 10. In a traveling wave tube this interaction means normally comprises a type of slow-wave structure such as the helix 42 which is supported in conventional manher by sapphire rods 43 within envelope portion 11 which in accordance with the invention is a molybdenum cylinder 44. Cylinder 44- is attached to metal member 25 as by brazing, and is reinforced by collar '46. A cupshaped closure 47 is brazed to metal member 25 and cylinder 44 to add rigidity and to cooperate with member 25 to form the end closure for the electron gun envelope.

In order to couple the input signal onto the helix 42, a coaxial line is brought longitudinally through the gun, rather than radially out of envelope portion 11 as is customary. A unique arrangement for providing the coaxial line comprises a ceramic rod 49 metalized by conventional metalizing procedures on its outside surface to provide the outer conductor 50. The inner conductor of the line is provided by a wire 51 located in a central bore in rod 49. The end of helix 42 projects {through a ceramic plug 52 inserted in a notch in the end of cylinder 44 and is attached to wire 51 of the coaxial line.

Wire 51 is brazed in rod 49 at the end where the rod enters closure cup 47. This is done to prevent air from leaking along wire 51 into the tube. Rod 49 is brazed in an aperture in metal member 25 for rigidity. Metal members 17 -23 are provided with oversized apertures through which rod 49 passes without contacting them. Metal member 16 provides the closure for the evacuated gun envelope, and rod 49 is brazed to member 16 to form a vacuum-tight seal therewith. An exhaust tubulation 55 is also brazed to metal member 16.

In order to shield the electron gun from stray radio frequency fields and from magnetic fields, metal member 25 is made of magnetic material such as iron, prefera'bly nickel plated, and is extended by an iron cylinder 56 which projects beyond the gun envelope. A continuous housing for the electron gun is completed by the use of brass disc 57, apertured at 58 to accommodate wires 26-30. Disc 57 is not made of magnetic material because it has been found that if the gun is completely shielded it will for some reason exhibit slight instability. In order to permit the tube to operate in humid atmosphere and at high altitude, and to increase mechanical stability, the space between

members

56, 57 and the gun envelope is filled with a moisture proof plastic material such as silicone rubber.

Corning now to the coupling arrangement for the coaxial input line, it will be seen that disc 57 has attached thereto a threaded boss 60 to which a conventional coaxial line can be attached. lA conical metal piece 61 is brazed to boss 60 and metalizing 50 to provide continuation of the outer conductor 50. A metal pin 62 is slotted at its inner end so as to fit tightly within ceramic rod 49 and tightly receive the end of wire 51. The outer end of pin 62 is bored and slotted to provide a receptacle for the inner conductor of a conventional coaxial line. A sleeve 63 of plastic material, such as the type sold under the trade name Teflon, is pressed between pin 62 and boss 60.

The collector end of the tube comprises an extension of cylinder 44, and for convenience in manufacture the extension is made of a separate metal cylinder 65. C01- lector 12 consists of a block of metal such as copper having a bore 66 therein Which is inclined relative to the tube axis so that secondary electrons emitted from the Walls thereof will tend to be trapped and not travel back down the helix. Of course the open end of bore 66 is in line with the axis of the tube. The upper surface of the collector is also inclined relative to the tube axis so that it will cooperate with other structure (hereinafter described) in such a way that an output coupling can pass longitudinally through the collector end of the tube without increasing the diameter of the envelope at the collector end over the diameter of the envelope portion through which helix 42 passes.

A unique output arrangement is provided which utilizes the envelope cylinder 65 as the outer conductor, partly in cooperation with the tapered upper surface of collector 12. The inner conductor is provided by a conical metal rod 67. The small end of rod 67 has a bore therein which receives a small metal tube 68. Tube 68 is brazed in the bore and provides a support for the small end of rod 67. The tube 68 is in turn supported in a ceramic sleeve 69 which is brazed to the top of collector 12, and the end of helix 42 is brazed in the end of tube 68. Cylinder 65 has a separate segment 71 which is brazed in place after items 68 and 69 have been properly po sitioned.

The end of cylinder 65 is sealed in a vacuum-tight manner by a ceramic button 72 which is metalized on its outer periphery and brazed in the cylinder 65. The outer end of button 72 is bored to receive the left end of a metal rod 73, and the right end of a metal pin 74. The bore in button 72 is metalized and is brazed to rod 73 and pin 74. A sleeve of insulating material such as the type sold under the trade name Teflon is pressed between rod 73 and cylinder 65. The outer end of rod 73 is bored and slotted to receive the inner conductor of a conventional coaxial line coupling.

It will be seen that the structure thus far described provides a tube having an elongated envelope portion, including cylinder 44 and 65, which is of uniform small diameter everywhere to the right of gun 10, as seen in Figures 1 and 6. In order to take full advantage of this construction, a cooling structure 76 is made in such a way as to be removable. Thus, the elongated envelope portion 11 can be inserted in a magnetic circuit having a very small inner diameter. In order to be removable, cooler 76, including its cooling fins 77, is slotted at 78 as shown in Figures 4 and 5. Bolts 80 pass through the cooler and serve to clamp the cooler onto cylinder 65. Bolts 80 must be loosened and cooler 76 removed each time the tube is removed from the magnetic circuitry. As shown in Figure l, the right end of cooler 76 extends past cylinder 65 and is threaded externally to provide an outer conductor to which the outer conductor of a conventional coaxial line coupling can be attached.

The tube shown in Figure 1 can be used in a magnetic circuit using either permanent magnets or a magnet coil, the latter being shown by way of example in Figure 6. The magnetic circuit comprises an inner cylinder 83 of non-magnetic material, an outer cylinder 84 of magnetic material and

end plates

85 and 86 of magnetic material. End plate 85 has a collar 88 projecting therefrom and carrying three or four screws 89 for supporting the tube in the magnetic circuit. Preferably, abutment discs 90 are attached to screws 89 to provide better contact with cooling fins 77. Collar 88 is provided with four apertures 91 to permit the flow of cooling air and to provide access to bolt 89 on the left end of the cooler.

End plate 86 has projecting therefrom a collar 93 having a cylindrical liner 94. The liner carries three or four set screws 95 for supporting the gun end of the tube, and collar 93 is provided with apertures 96 to permit access to screws 95. The end of collar 93 is threaded to receive a cap 97 which clamps the tube axially in the magnetic circuit.

In order to provide a firm support for the tube throughout the length of envelope portion 11 and yet permit slight radial adjustment of the tube relative to the magnetic circuit, a slight space is left between the outside of the tube and the inside of cylinder 83, and this space is filled with resilient material such as silicone rubber. In order that the rubber filling will not prevent removal of a tube from the circuit, a sleeve 98, having an end flange 100, is inserted in cylinder 83 and is removable with the tube. Under this arrangement the rubber filling is specifically located in the space between the tube and the sleeve 98. Liner 94 is also removable with the tube for the same reasons as sleeve 98. In view of the presence of the rubber filling, screws 89 and 95 can be used to provide slight radial adjustment of the tube within the magnetic circuit.

Although the invention relates primarily to traveling wave tubes, it should be understood that certain broader teachings thereof are adaptable by those skilled in the art for use in other types of tubes.

Having thus described the invention, What is claimed as new and desired to be secured by Letters Patent is:

1. A traveling wave tube comprising an electron gun having cathode means for initiating a solid beam of electrons, an elongated tubular metallic envelope portion connected to said gun, a collector in the end of said envelope portion remote from said gun and contacting the interior of the envelope in heat exchanging relation, a slow-wave structure in said elongated metallic envelope portion and surrounding said beam of electrons, an input conductor coupled to the gun end of said slow-wave structure, an output conductor coupled to the collector end of said slow-wave structure, said output conductor passing through said collector and out the end of said traveling wave tube adjacent said collector, and a cooling structure removably connected to the traveling wave tube at the collector end thereof, said cooling structure being tubular and surrounding said envelope portion in heat exchanging proximity to said collector.

2. A traveling wave tube comprising an electron gun having cathode means for initiating a solid beam of electrons, an elongated tubular metallic envelope portion connected to said gun, a collector in the end of said envelope portion remote from said gun and contacting the interior of the envelope in heat exchanging relation, a slow-wave structure in said elongated metallic envelope port1on and surrounding said beam of electrons, an input conductor coupled to the gun end of said slow-wave structure, said input conductor passing through said electron gun in transversely spaced relation to said cathode, an output conductor coupled to the collector end of said slow-wave structure, said output conductor passing through said collector in insulating relation thereto and out the end of said traveling wave tube adjacent said collector, and a cooling structure removably connected to the traveling wave tube at the collector end thereof, said cooling structure being tubular and surrounding said envelope portion, said collector and said output conductor 1n heat exchanging proximity to said collector.

3. A traveling wave tube comprising an elongated metal cylinder forming a portion of the vacuum-tight envelope for said tube, an electron gun connected to one end of said cylinder, said gun projecting a solid beam of electrons axially within said cylinder, a collector positioned in the other end of said cylinder for receiving said beam of electrons, a slow-wave structure supported on the inner surface of said cylinder and surrounding said beam of electrons, an input conductor coupled to the gun end of said slow-wave structure, and a coaxial output line coupled to the collector end of said slow-Wave structure, the inner conductor of said output line passing through said collector and out the end of said cylinder adjacent said collector, the outer conductor of said output line being formed in part by said collector and in part by the end of said cylinder adjacent said collector.

4. A traveling wave tube comprising an elongated metal cylinder forming a portion of the vacuum-tight envelope for said tube, an electron gun connected to one end of said cylinder, said gun projecting a solid beam of electrons axially within said cylinder, a collector positioned in the other end of said cylinder for receiving said beam of electrons, a slow-wave structure supported on the inner surface of said cylinder and surrounding said beam of electrons, an input conductor coupled to the gun end of said slow-wave structure, a coaxial output line coupled to the collector end of said slow-wave structure, the inner conductor of said coaxial output line passing through said collector in insulated relation thereto and out the end of said cylinder adjacent said collector, a tubular cooling structure, and means for removably clamping said cooling structure around said cylinder in heat exchanging proximity to said collector, an extension of said cooling structure surrounding the extending end of said inner conductor and forming a portion of the outer conductor of said coaxial output line.

5. A traveling wave tube comprising an electron gun, an elongated envelope portion connected to said gun, a collector at the end of said envelope portion remote from said gun, a slow-Wave structure in said envelope portion, an output conductor coupled to the collector end of said slow-wave structure, an input conductor coupled to the gun end of said slow-Wave structure, said input conductor being a coaxial line and comprising a rod of insulating material, a metallic coating on the outside of said rod and forming the external conductor of said line, a wire connected to said slow-wave structure and passing along an axial bore in said rod, said wire forming the inner conductor of said coaxial line, said rod of insulating material passing through said electron gun and extending outside the envelope of said traveling Wave tube, and said output conductor passing through the end of said traveling Wave tube adjacent said collector.

6. A traveling wave tube having an electron gun comprising an envelope formed of ceramic rings sandwiched between metal members having annular surfaces engaged by the ceramic rings, said ceramic rings being metalized on their ends, and metallic bonds joining said metalized ends to the annular surfaces of the adjacent metal members, a cathode connected to one of said metal members, a second one of said metal members extending across one end of said gun and having a first aperture in line with said cathode, a third one of said metal members forming a closure for the other end of said gun, a metal cylinder connected to said second metal member and extending away from said gun in line with said cathode, a collector at the distal end of said cylinder, a slow-wave structure in said cylinder, said second and third metal members of said gun having apertures therein, offset from the said first aperture and in line with each. other, a rod of insulating material passing through said offset apertures, metalizing on the outside of said rod and forming the outer conductor of a coaxial input line, vacuum tight seals between said metalizing on the outside of said rod and the peripheries of said apertures, and a wire passing through a bore in said rod and forming the inner conductor of said line, said wire being connected to said slow-wave structure.

7. A beam type tube having an electron gun comprising an envelope formed of ceramic rings sandwiched between metal members having annular surfaces engaged by the ceramic rings, said ceramic rings being metalized on their ends, and metallic bonds joining said metalized ends to the annular surfaces of the adjacent metal members, a cathode connected to one of said metal members, a second one of said metal members forming a closure for one end of said gun, a third one of said metal members extending across one end of said gun and having an aperture in line with said cathode, an elongated envelope portion connected to said gun, radio-frequency interaction means in said envelope portion, and a cup of metal surrounding the envelope of said gun, the open end of said cup being attached to said third metal member, said third metal member and the side wall of said cup being of magnetic material, the bottom of said cup being of nonmagnetic material.

8. A beam type tube having an electron gun comprising an envelope formed of ceramic rings sandwiched between metal members having annular surfaces engaged by the ceramic rings, said ceramic rings being metalized on their ends, and metallic bonds joining said metalized ends to the annular surfaces of the adjacent metal members, a cathode connected to one of said metal members, a second one of said metal members forming a closure for one end of said gun, a third one of said metal members extending across one end of said gun and having an aperture in line with said cathode, an elongated envelope portion connected to said gun, radiofrequency interaction means in said envelope portion, a cup of metal surrounding the envelope of said gun, the open end of said cup being attached to said. third metal member, and plastic insulating material filling the space between the envelope of said gun and said cup.

9. A beam type as claimed in claim 8 in which said third metal member and the side walls of said cup are of magnetic material and the bottom of said cup is of nonmagnetic material.

10. A traveling wave tube comprising an electron gun including a cathode, an elongated envelope portion connected to said gun in line with said cathode, said envelope portion comprising at the end thereof remote from said gun a metal cylinder, a block of metal in said cylinder and forming a collector, a bore in said collector having an open end in line with said cathode, a slow-Wave structure in said envelope portion between said gun and said collector, and an output connector for said slow-wave structure comprising an inner conductor passing through said metal cylinder in insulatingly spaced relation to said collector and to said cylinder, said inner conductor being connected to said slow-wave structure, and said metal cylinder forming the outer conductor of said output connector.

11. A traveling wave tube comprising an electron gun including a cathode, an elongated envelope portion connected to said gun in line with said cathode, said envelope portion comprising at the end thereof remote from said gun a metal cylinder, a block of metal in said cylinder and forming a collector, a bore in said collector having an open end in line with said cathode, the axis of said bore being inclined with respect to the axis of said elongated envelope portion, a slow-Wave structure in said envelope portion between said gun and said collector, and an output connector for said slow-Wave structure comprising an inner conductor passing through said metal cylinder in insulatingly spaced relation to said collector and to said cylinder, said inner conductor being connected to said slow-Wave structure, and said metal cylinder forming the outer conductor of said output connector, said collector being tapered and having its smallest cross-sectional area at its end remote from said gun, and said inner conductor being tapered and having its largest cross-sectional area at its end remote from said gun.

12. Electron tube apparatus comprising a traveling wave tube having an electron gun, an elongated tubular envelope portion attached to said gun, a collector in the end of said tubular envelope portion remote from said gun, a slow-wave structure in said envelope portion, an input coupling for said slow-Wave structure extending through said gun, an output coupling for said slow wave structure extending through said collector and out the end of said tubular envelope portion, a tubular cooler surrounding said envelope portion in heat exchanging proximity to said collector, a magnetic circuit comprising a coil, a-core cylinder inside said coil, end plates at each end of said core, magnetic means joining said end plates, externally of said coil, said traveling Wave tube being positioned within said magnetic circuit with said core cylinder surrounding said elongated envelope portion, the outside diameter of said electron gun being greater than the inside diameter of said core cylinder, and the outside diameter of said cooler being larger than the inside diameter of said core cylinder, and means removably attaching said cooler to said elongated envelope portion.

ReferencesCited in the file of this patent UNITED STATES PATENTS 2,443,916 Kelar June 22, 1948 2,602,148 Pierce July 1, 1952 2,615,141 Hansell Got. 21, 1952 2,643,353 Dewey June 23, 1953 2,645,737 Field July 14, 1953 2,680,209 Veronda June 1, 1954 2,683,831 Skehan July 13, 1954 2,774,006 Field et al. Dec. 11, 1956 2,800,603 Bryant et al. July 23, 1957 2,809,321 Johnson et al. Oct. 8, 1957 2,812,467 Konipfner Nov. 5, 1957 2,817,037 Peter Dec. 17, 1957 2,824,257 Branch Feb. 18, 1958 2,843,791 Pierce 'July 15, 1958 7 2,871,397. Priest et al. Jan. 27, 1959 FOREIGN PATENTS 762,105 Great Britain Nov. 21, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,984,762 May 16 1961 Laird K, S, Haas It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 31, for "hte" read the column 2, line 16 for "electrical" read cylindrical column 6 line 56 after "type" insert tube column 8, line 2 after I "plates" strike out the comma.

Signed and sealed this 17th day of October 1961a (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC