A New Electron Bombardment Type Ion Gun for High Brightness Metal Ion Beam

Abstract

If a metal target is bombarded by the high power density electron beam, the target material are made to evaporate and the evaporated atoms will be ionized by collision with the incident electrons. As these ions have lower energy than several electron volts, the incident electron beam can trap these ions in the potential valley of space charges. The trapped ions are diffused and accelerated toward the electron cathode which have the hole in the centre (in practice the spirally wound tantalum wire was used). And the ions are taken out through this cathode hole.Ion beams got by above process have fine diameter and low aperture angle, then the brightness of ion beam become higher in itself though the total ion current is not so high.Several metals as Cr, Si, Mg-Al alloy and others were used as targets. In the case of Mg-Al target the values of normalized brightness of the ion beam reached the order of 2×10-94.6×1010 A/m2 ·rad2. And the masses of ion beam components were analyzed by using the circular pole magnet.This ion gun will be usable as a fine metal ion source and a mass analyzer of target material.