Development of radio frequency induction plasma generators for neutral beams

The techniques, operational aspects, and experimental results of a radio frequency induction plasma generator, with an internal rf power coupler, intended for intense neutral beam applications are described. One of the development sources suitable for 10×10-cm2 extraction optics was operated to a deuterium ion current density of 250 mA/cm2, uniform to 5%, over a circular extraction area 15 cm in diameter with a coupled rf power of 20 kW. Temporal fluctuation levels in the extracted ion current were measured to be typically 1% of the dc level. A second developmental source suitable for 10×40-cm2 grid sets was operated to 200 mA/cm2, uniform to ±8% over a 10×40 cm2 area, with 40-kW coupled rf power.