GB985339A - Improvements relating to cathode structures - Google Patents

Abstract

985,339. Cathode constructions. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Nov. 29, 1963 [Sept. 5, 1962], No. 34043/62. Heading H1D. [Also in Division H5] A thermionic cathode-e.g. for the electron gun of a klystron tube-has a concave electron emissive front face; a zone of reduced thickness adjacent its peripheral support to reduce heat conduction thereto; and a radiant heater disposed adjacent the outer zone of the rear face such that the central zone of the cathode is heated by conduction from the outer zone and only to a small extent by direct radiation, whereby to increase the uniformity of temperature over the cathode surface. The heater of the cathode 1, with emissive surface 2, is constituted by four resistance wires 13 connected in spiral fashion between inner terminals 5 on a conductive disc 3, which is free to rotate about its axis on an insulating pin 4 to allow for expansion, and outer terminals 8, one pair of which is electrically connected to plate 7, supported by stainless steel or molybdenum pillars 12 which constitute one terminal of an A.C. supply, the other supply terminal 11 being connected to the other pair of terminals 8 via plate 6, whereby the current in adjacent wires flows in opposite directions. The cathode is supported by molybdenum ring 15 having tabs 17, 18 projecting into recesses in the peripheral flange 14 of the cathode, and in the beam electrode 16, respectively, the portion 14 of reduced thickness reducing heat conduction therebetween. The cathode is displaced in opposite directions by expansion of ring 15 and of pillars 12, the materials of the latter being chosen such that their effects substantially cancel, minimizing variation of the cathodeanode spacing. Nickel reflectors 19, 20 surround the heater-cathode assembly. The gun, the housing of which may extend into an oil bath for cooling, further includes an axially apertured anode (not shown).