GB684710A - Improvements relating to high vacuum pumps - Google Patents

Abstract

684,710. Producing high vacua. ASSOCIATED ELECTRICAL INDUSTRIES, Ltd. June 1, 1951 [July 19, 1950], No. 18054/50. Class 8 (i). A high vacuum pump comprises a tube 1 communicating with a space to be evacuated and containing an apertured anode 8, a cathode 9 and a grid-like electrode 10 which is preferably held at negative potential relative to the cathode; gas molecules diffusing into the tube from the space to be evacuated are ionised by a stream of electrons emitted from the cathode which is heated. and the positive ions thus produced are accelerated towards and through the electrode 10 and out of the tube preferably to a backing pump. A magnetic ion lens 7, or an electrostatic ion lens, is used to concentrate or focus the stream of positive ions. A transverse magnetic field may be applied to the ionising region thereby causing the electrons emitted by the cathode, which may comprise a single straight wire of tungsten, to follow a cycloidal path 9' and thus increase the ionising efficiency. In another embodiment the cathode is combined with the electrode 10. In a modification, Fig. 3, the tube contains a cylindrical anode 13, supplied with a potential of about 5.000 volts, disposed between apertured negative electrodes 14, 15. A coil 16 provides an axial magnetic field which accelerates the ions, produced by virtue of a stable gas discharge in the ionising region, in an outward direction. The ions passing upwardly through the electrode 14 are stopped by a baffle 19 whilst the remainder pass through the electrode 15 to the backing pump after being concentrated or focused by the magnetic coil 16 or by a separate magnetic coil.