| 摘要 |
1,159,303. Thermionic cathodes. SIEMENS A.G. 28 March, 1967 [29 March. 1966], No. 14008/67. Heading H1D. An electron beam generating system, e.g. for travelling wave tubes, comprises at one end of a hollow support 2 a porous emission substance carrier plate 1 which forms the main emissive surface and which is heated by the impact of the discharge from a secondary dispenser cathode 11, which is housed in the other end of the support 2 and which is raised to its operating temperature by a supplementary heater 5, which is subsequently switched off, the heat generated at the main carrier plate 1 being sufficient, when fed back to the secondary cathode via support 2, to maintain the secondary cathode at its operating temperature. As shown in Fig. 1, the supplementary heater may be an insulated coil of tungsten wire which is cemented to cylindrical portion 4 of support 2 by beryllium oxide, to improve the heat transfer. The supplementary heater may be automatically switched off at a preset temperature, e.g. by reference to its own resistance value, and may be connected in parallel to the discharge section between porous plates 1 and 12. Alternatively, Fig. 2 (not shown), the supplementary heater may be an H.F. induction coil. In a further embodiment, Fig. 3 (not shown), the secondary cathode, comprising a cylindrical charge store closed at each end by a porous plate, may be housed enclosed within the main cathode which similarly comprises a porous plate closing each end of a hollow support. The auxiliary discharge from the other end of the main cathode may be used to activate a getter, e.g. Mo or C coated with Zr. The main cathode need not have its own store of emissive material but may instead be supplied by the secondary cathode. The porous emission substance carrier plates may be of carbon. |
