GB1172159A - Improvements in Low Voltage Electron Beam Apparatus - Google Patents

Abstract

1,172,159. Electron guns. GENERAL ELECTRIC CO. 23 March, 1967 [31 May, 1966], No. 13849/67. Heading H1D. A hollow cathode electron beam source, e.g. in apparatus for welding, heating or processing materials, comprises a perforated or solid wall cathode structure 7 divided by a partition 27 into at least two cathode chambers interconnected through an aperture 28 in the partition. With suitable gases, e.g. He, A, N or H, gas pressures, voltages and dimensions, a plasma body is formed in each cathode chamber, the plasma bodies being coupled together through the aperture. Insulation may be interposed between the two cathode chambers and the chambers biased to different voltages (Figs. 4 and 5). In one variation, Fig. 6, the insulation 40, e.g. of ceramic, also envelops the side walls of the cathode structure. The ceramic sheath may comprise secondary electron emissive material such as magnesium oxide to act as a further source of electrons for the plasmas due to ion bombardment. The cathode structure may be surrounded by a metal shield (Fig. 3). In other variations the partition 27 need not be perpendicular to the side walls, Fig. 7, or two or more partitions may be provided to form a three- or multiple-stage cathode, Fig. 8. In a further embodiment six or more cathode chambers are interconnected in a series-parallel arrangement (Figs. 9a, 9b). The cathode chambers may be cylindrical, rectangular or square in shape and the beam exit aperture circular or rectangular. The source may be operated with D.C. or A.C. voltages and may produce a pulsating beam.