Patent GB-819660-A (GB)
Title: Velocity modulation electron tube apparatus
IPC: H01J25/24
Filed: 1956-06-12
Abstract: 819,660. Velocity modulated tubes. VARIAN ASSOCIATES. June 12, 1956 [June 17, 1955], No. 18171/56. Class 39(1). A velocity modulation electron tube has one end sealed by a mounting member and the other sealed end supporting at least one external cavity resonator and having a window sealed therein, the mounting member supporting the cathode and other tube elements so that in assembly the cavity resonator and window are sealed to the said other sealed end and the mounting member carrying its elements is brought to the first end of the envelope and sealed thereto, cooperating portions of the tube structure engaging one another to ensure that the internal cavity resonator is correctly aligned with respect to the tube elements. The tube elements including the cathode may be the gun and collector or gun and reflector. In one form, Fig. 1, a cylindrical metal envelope 6 is crimped into four recesses 1<SP>1</SP> in the base 1 and is sealed at one end to a waveguide flange which carries cavity resonator 26 which comprises two stamped sheet portions brazed together. In assembly the waveguide flange 28, envelope 4, ceramic waveguide window 29, resonator 26 tube 32 carrying accelerator and resonator grids 33, 34 and resonator grid 35 are assembled as a unitary structure and mounting stem 5 mica discs 11, 12, cathode 18, focusing electrode 19 and reflector are formed as a second unitary structure and slipped into the envelope so that the resonator 26 passes through the openings in discs 11, 12 until disc 4<SP>1</SP>, contacts the step in envelope 4 the contacting parts being brazed together, rods 22 ensuring correct alignment of the cathode and reflector with respect to the resonator grids. The resonator is held firmly in the apertures of discs 11, 12 by four tabs projecting from the edges of the disc aperture and by the end flanges of the resonator. The mica discs 11, 12 are mounted on wires 8 by eyelets the wires 8 being sealed through glass stem base 9 and soldered to base prongs 9. U-shaped members 16, 23 between mica discs 11, 12 are locked thereto by bent over tabs, the cathode heater, cathode and focusing electrode being fixed to 16 and the reflector to 23, heads 8 are flexible only if spacer rods 22 are used ; 22 are unnecessary if proper jigging is used. Even with a bifilar heater there is a small stray magnetic field produced by the end turn of the heater coil and by minor asymmetries which modulates the beam at 60 cps. and produces "FM noise". This is avoided by magnetic screening which may be effected by a coating or sheet of material welded or otherwise attached on or to the rear side of the cathode button or by making the cathode button of Ni-Co alloy. A magnetic shield can be similarly employed in the folded heaters used in Figs. 10-13 (not shown). In a modification, Fig. 4 (not shown),the discs 11, 12 are held in grooves in an antivibration shell. In another modification, Fig. 5 (not shown), there are two semicylindrical shells separated by a mica disc the cathode and focusing electrode being welded to one shell and the reflector to the other shell. In another form Fig. 6, the cathode 54 and reflector 61 are mounted in an aperture in ceramic disc 51, which is brazed to envelope 4 or held by annular grooves or by dimples. In the latter case the upper groove or row of dimples is formed first, disc 51 inserted and the lower groove or set of dimples then formed. The disc 51 is mounted on wires 8 by eyelets or by direct brazing. The reflector is secured to ceramic disc 51 by rivets 63 passing through U-bracket 62 and the cathode focusing electrode assembly by four straps 58. The focusing electrode is mounted from the cathode by small wires 55. The method of assembly is similar to that of Fig. 1, the gunreflector-stem-disc 51 assembly being inserted from the lower end of the tube. An external cavity with a turning screw and a window coupling screw can be coupled to the internal resonator, Fig. 8 (not shown). The external resonator may be of cylindrical or, in Fig. 9 (not shown), of rectangular section. In other forms a two resonator klystron oscillator or amplifier is formed, the two resonators having a common wall, Figs. 10, 11 (not shown). In these forms the wires can be taken through eyelets filled with glass in a disc similar to 6, Fig. 1, to the base prongs. In the two resonator klystron the assembly is slightly different the waveguide flange, envelope, cavity resonators and collector being one subassembly and the mounting discs, coaxial input line and cathode a second subassembly inserted into the first subassembly. The invention can be applied to a " floating kidney " tube, Figs. 12, 13 (not shown), the floating drift tube being mounted on a flat rectangular member which may or may not be insulated from the resonator wall ; in the former case modulating potentials may be applied to the drift tube. An external tunable cavity can be added as in Figs. 8, 9 (not shown). In another embodiment, Figs. 14, 15 (not shown), having an external tunable cavity the latter cavity is if desired made approximately rectangular by partitions inserted into the cavity cylinder ; the partitions can be replaced by solid blocks. In a thermally tuned reflex klystron, Fig. 16, the electrodes are supported from disc 105 by mica discs 95, 98 the cathode-focusing electrode assembly being supported from disc 95 by a metal bracket 96, while the reflector 99 is mounted on three wires 8 and braced by members 101. A U-shaped mica disc 98 is mounted on wires 8. When the second subassembly comprising cathode-focusing electrode 97 auxiliary annular gun 104, reflector 99 and stem 5 has been inserted into the envelope to the correct position, 105 is brazed to the envelope. For pretuning, the envelope is pressed at 106, the motion being transmitted through U-bracket 90 to resonator tube 93, diaphragm 92 flexing. The tube is now set at the right upper frequency limit of the desired band and thermal tuning is achieved by means of auxiliary annular gun bombarding conical resonator part 94 of high heat expansion i.e. by varying the potential between the auxiliary cathode and 94. The remaining parts of the resonator and bracket 90 have low heat expansion characteristics. In a modification, Fig. 18, the thermal tuner has a coated spherical cathode which emits a hollow conical beam under the focusing action of conical focusing electrode 110 and cup shield 111 which also shields the reflector 107 from electron bombardment. Shield 111 is carried by braces 112. All the seals in all embodiments are made by brazing.