GB744882A - Improvements in or relating to ion sources - Google Patents

Abstract

744,882. Discharge apparatus. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Nov. 30, 1953 [Dec. 3, 1952], No. 33191/53. Class 39 (1). An ion source comprises a plurality of cylindrical grids 2, 3, coaxial with the cathode 1, and a cylindrical anode 4 coaxial with the cathode and having one or more slits 5 parallel to the cathode to allow passage of the negative ions, the anode being at such a small negative potential relative to the outer grid electrode 3 and the outer grid electrode being so constructed that the electrons are mainly intercepted by the anode. The negative ion beams which pass through the slits 5 are, by means of the focusing and accelerating electrodes 6 and 7, fed to the analyser of a mass spectrometer, to a mass separator or to a leak detector. The potential of the anode 4 relative to the cathode 1 is approximately 145 volts positive and that of the grid 3 approximately 150 volts positive. Additional plate electrodes 9, 10 can be arranged outside an aperture 8 in the anode 4 and between the anode and outer grid 3 respectively, and having a voltage negative relative to the cathode for the collection of positive ions, the rate of ion-collection being used as a measure of the pressure in the ionisation chamber, a switch interrupting the cathode current when the pressure is excessive. In addition to the constant bias an alternating voltage may be applied to the grid 3 and the electrodes 9 and 10 may have A.C. amplifiers connected to them.