Suppression of Radial Divergence of Extremely Low Energy Ion Beam by an Electron Beam Injection to a Grounded Electrode

Transition to a highly focused state is observed in a hydrogen ion beam extracted from an ion source using concave-shaped electrodes. The beam has a low energy (similar to 95 eV) and a high current (similar to 60 mA) with a similar to 60mm diameter. The transition is induced by electron beam injection (1 keV and up to 50 mA) to a grounded electrode of an ion source from a direction obliquely opposite to the ion beam velocity. Probably, secondary electrons emitted from the electrode play an effective role in cancelling the beam ion space charge, since they are produced in the core region of ion beam immediately after the extraction. Comparison between the cases with and without an electron beam exhibits great improvements not only in a total ion beam current reaching a target, but also in the focusing of ion beam. The sudden transition to this highly focused state, which is triggered by a low electron beam current (similar to 9 mA), suggests that some kind of a nonlinear process plays an essential role in this focusing. (C) 2013 The Japan Society of Applied Physics