GB895002A - Improvements in and relating to high vacuum ion pumps - Google Patents

Abstract

895,002. Ion pumps. COMPAGNIE FRANCAISE THOMSON-HOUSTON. Feb. 13, 1959 [Feb. 13, 1958], No 5142/59. Class 39 (1). In a magnetron-type ion pump having an annular discharge space between an anode and a hollow cathode, the cathode is apertured for the passage of ionised gas particles. In the arrangement shown, an anode structure 13 provided with cooling fins 14 has a cylindrical surface 11, surrounding a cylindrical cathode 12 preferably consisting, at least at its surface, of secondary electron emitting material and formed by bars 15 the ends of which are inserted in radial rests in support rings 16 and 17 which also carry electron reflecting shields 18 and 19. Gas entering an inlet port OP passes between three supporting arms (of which two, 23 and 24, are shown) of a conical auxiliary electrode 22 which is maintained at a positive potential and deflects ions arriving inside the cathode 12 to an outlet port OP where they are collected on the wall of a pipe 20 which provides connection to a primary pumping system or on a separate electrode provided for the purpose. Magnet poles N and S provide an axial magnetic field. A ceramic ring 21 closes one end of the cathode and insulates the auxiliary electrode 22 from the cathode. The anode 13 may be provided with cavities as in a conventional magnetron. A getter means may be provided instead of or in addition to the primary pumping system and Figs. 3 and 4 (not shown) illustrate two arrangements in which the gas particles are completely removed by gettering so that the outlet port OP is dispensed with and the auxiliary electrode 22 is replaced by a hollow cylindrical electrode located inside the cathode and having a gettering surface of tantalum, which is also a secondary electron emitter, or alternatively of titanium. In one arrangement an auxiliary thermionic cathode co-operating with the anode, and in the other arrangement an auxiliary electrode co-operating with a sharp ridge on the main cathode, is provided for starting purposes. The main electrode system may be energised by D.C. or by A.C. or by pulses. An alternative form of apertured cathode may be produced by winding one or more conductors in spaced helical turns.