High-current metal ion beam extraction from a multicusp ion source

Abstract

Improvements have been made in a multicusp ion source, which made it possible to produce metal–vapor plasma and extract a high-current metal ion beam. In the discharge chamber, double radiation shields were set and the inner shields were heated to 1860 K. Therefore, it became possible to maintain enough metal–vapor density to produce plasma without the use of support gas. For the extraction of a high-current metal ion beam, we used multislit electrodes in the accel–decel electrode structure. Experiments of the metal ion beam extraction were performed with several kinds of metals (Al, Cr, Si). For example, the extracted Al ion beam current reached 65 mA. As a result of mass analysis, it was found that more than 90% of an Al ion beam is Al+. Furthermore, stable operation could be achieved. For Al (58 mA) and Si (28 mA) ion beam extraction, the temporal drift of each ion beam current was within ±5% for 3 h.