Development and testing of a prototype long pulse ion source for the KSTAR NBI system

Summary form only given. A prototype long pulse ion source (300 s) has been developed, and beam extraction experiments of the ion source were carried out in the Neutral Beam Test Stand (NBTS) of the KSTAR. The ion source consists of a magnetic bucket plasma generator with multi-pole cusp fields and a set of tetrode accelerator with circular apertures. Arc discharges of plasma generator have been controlled precisely by the emission-limited mode, controlled by the applied heating voltage of cathode filaments. Efficient and stable arc plasmas with a maximum arc power of 100 kW have been produced by the constant power mode operation of arc power supply. A maximum ion density of 8/spl times/10/sup 11/ cm/sup -3/ was obtained by using electrostatic probes, and an optimum arc efficiency of 0.46 A/kW was estimated with arc powers and a total beam area. Optimum beam perveance deduced from the ratio of gradient grid current to total beam current was 0.7 /spl mu/perv. The experimental results of beam extraction obtained at the accelerating voltage of 70 kV appear less than the expected.