Patent GB-801804-A (GB)
Title: Klystron amplifier
Inventor: ZITELLI LOUIS THOMAS
IPC: H01J25/12
Filed: 1955-08-16
Abstract: 801,804. Velocity-modulated tubes. VARIAN ASSOCIATES. Aug. 16, 1955, No. 23609/55. Class 39(1). In a klystron amplifier comprising a tube in which an electron beam passes through a plurality of cavity resonators in succession, means are provided for applying a focussing magnetic field to all but the last cavity. The tube shown comprises four cavity resonators 3, 4, 5 and 6 machined out of a solid block 2. The electron beam passes from an emitter 7 through an aperture 13 in an accelerating anode 12 and drift tubes 14, 15, 16, 17 and 19 to a copper collecting electrode 21 provided with cooling fins 22. A lead (not shown) connects one of the fins 22 to the block 2 to maintain the collector electrode 21 at the same potential as the block 2. The ends of the drift tubes are bevelled to reduce secondary emission effects. The input and output resonators 3 and 6 communicate through windows or irises 25 and 29 with input and output waveguides 26 and 30 of heavy copper construction terminating in coupling flanges 27 and 31 provided with mica windows 28 and 32. A heavy copper block 33 interposed between the waveguides 26 and 30 is provided with cooling fins 34 which extend to cover part of the block 2. The electron beam is focussed by two U-shaped magnets (not shown) one on each side of the tube. Two legs of the magnets are connected to an iron ring member 37 fixed to the accelerating anode 12 which is also made of iron or other magnetic material and forms one of the pole pieces. The other pole piece is an annular plate 38 which is interposed between the resonator 5 and the output resonator 6 and has part of its periphery engaged by two shoe members 39 connected one to each of the other legs of the magnets. The reduction in the length of the magnet gap results in a substantial saving in magnet weight and size, and the exclusion of the focussing magnetic field from the output cavity 6, in which the radio frequency field is extremely large, prevents multifactor action which would otherwise occur between the bevelled ends of drift tubes 17 and 19. A portion of drift tube 17 and drift tube 19 have slightly enlarged bores 45 and 46 to allow for a slight expansion of the electron beam due to the absence of the focussing field from resonator 6. Each cavity resonator has a flexible side wall 48, Fig. 3A, to which is brazed a pedestal member 52. A stainless steel screw 53 secured in a threaded bore in an aluminium rod 54 by a set screw 55 is brazed in a recess in the member 52. A stainless steel sleeve 57 provided with a screwdriver slot 61 has an external thread engaging a bridge member 58 and an internal thread engaging a threaded reduced portion 56 of the rod 54. The external and internal threads of the sleeve 57 are of slightly different pitch thus providing a differential screw action. The sleeve is turned to tune the resonator and then locked by a nut 62. The bridge member 58 is supported between two molybdenum rods (not shown) one on each side of and parallel to the aluminium rod 54 to provide automatic compensation for increases of cavity dimensions with rise in temperature. A removable cover 63 of plastic or plastic glass fibre combination ensures that the temperature of the tuning mechanism is substantially the same as that of the tube body.