BEAM-BUNCHING IN AN ECR ION-SOURCE BY THE PULSED GATING-POTENTIAL METHOD

A pulsed gating-potential method for millisecond beam-bunching has suc cessfully been applied to a single-stage 6.4 GHz ECR ion source. Depen ding on the repetition rate of a pulsed alternating potential of a few hundreds volts applied between the ECR chamber of the source and an e lectrode placed near its exit hole, two different time structures of t he bunched beam were observed; exponentially decaying and constant wit h time at sufficiently low and high repetition rates of the bunching p otential, respectively. Discussed are the possible ion source paramete rs of the ion source that affect the damping time of the bunched ion c urrents observed at low repetition rates of the bunching potential. At a high repetition rate of the potential, the magnitude of the bunched beam currents depends only on the length of the duty-off period; it i ncreases with decreasing duty factors.