GB879997A - Travelling wave tube - Google Patents

Abstract

879,997. Travelling wave tubes. HUGHES AIRCRAFT CO. Aug. 26, 1959 [Dec. 15, 1958], No. 29238/59. Class 39(1). In a travelling wave tube having a delay line comprising a plurality of cavity resonators each including two apertured discs spaced apart by the axial dimension of the cavity each cavity having drift tubes or other shielding means so disposed that the axial region of coupling moving downstream along the structure is progressively shifted upstream with respect to the centre of each of the cavities along the axis thereof and that the pairs of discs are equally spaced from each other and that synchronism is maintained between the decelerated stream and the structure without altering the electrical parameters of the cavities. The drift tube lengths and gap spacings may be equal Fig. 4 (not shown) or the drift tube lengths may be unequal, Fig. 2 with equal gap spacings. The delay line structure is integral with a permanent magnet structure (preferably periodic) for focusing the electron beam, or a separate solenoid may be used, Fig. 5 (not shown). The drift tubes 110, Fig 2, are formed on the inner ends of annular polepieces 16 interleaved with annular permanent magnets 14 of greater or equal external diameter which are diametrically split for ease of assembly between the polepieces. Cylindrical copper spacers 116 fit inside annular shoulders 114 on the polepieces. The spacers 116 carry channels 120 filled with brazing alloy for sealing during manufacture in an oven, and the entire inner surface of the cavities is plated with silver or gold. Each delay line cavity has a coupling aperture to the next cavity. The cavities are arranged in amplifier sections separated by isolator sections each comprising lossy ceramic buttons 128 Fig. 2 which completely absorb the wave while a shield 132 isolates them from the electron beam. The coupling holes between the cavities are made by an end mil. One or more sets of locating holes are provided in the polepieces and a notch opposite each kidney shaped coupling hole the latter hole extending over up to 60 degrees of arc. The magnets are made of metal or ceramic (ferrite). The cathode has a small opening to allow the gun to be aligned with the rest of the tube assembly, the focusing electrode is at cathode potential and the gun is surrounded by a heat shield. The envelope parts surrounding the gun and collector are alternately of metal and ceramic material and is described in detail with reference to Fig. 1 (not shown) the collector being water cooled and having a conical electron receiving surface. Other liquids or gases may replace water in the cooling system. The input and output waveguides have stepped impedance transformers and are linked by a T-shaped exhaust tube.