Beam-bunching in an ECR ion source by the pulsed gating-potential method

A pulsed gating-potential method for millisecond beam-bunching has successfully been applied to a single-stage 6.4 GHz ECR ion source. Depending on the repetition rate of a pulsed alternating potential of a few hundreds volts applied between the ECR chamber of the source and an electrode placed near its exit hole, two different time structures of the bunched beam were observed; exponentially decaying and constant with time at sufficiently low and high repetition rates of the bunching potential, respectively. Discussed are the possible ion source parameters of the ion source that affect the damping time of the bunched ion currents 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 increases with decreasing duty factors.