Initial beam extraction results of a prototype long pulse ion source for the KSTAR NBI heating system

Abstract

Summary form only given, as follows. Beam extraction experiments of a long pulse ion source (300 sec) were initiated in the NBI (neutral beam injection) heating system of the KSTAR (Korea Superconducting Tokamak Advanced Research) tokamak. The prototype ion source (beam power of 120 kV/65 A with deuterium, beam area of 13 /spl times/ 45 cm/sup 2/, 4 circular aperture grids made of copper) was designed to provide a high power arc discharge (120 V, 1200 A) in a magnetic bucket chamber with multi-pole cusp fields. Arc discharges were controlled precisely for the beam extraction by the emission-limited mode with control of filament heating voltage. A maximum ion density was measured by using a Langmuir probe, with the arc voltage range of 80-100 V. An optimum arc efficiency, 0.33 A/kW, of plasma generator was reached semi-empirically with the arc discharge power of 40-50 kW. An extractible maximum beam current was analytically about 35 A, when the accelerating voltage was 80 kV with a perveance of 9.5 microperv. Optimum perveance according to the minimum gradient grid current was obtained experimentally by the perveance scan at a fixed accelerating voltage. Finally, the results of optical diagnostics from an OMA (optical multi-channel analyzer) system were presented.