Initial experiments with a versatile multi-aperture negative-ion source and related improvements

摘要

A relatively compact ion source, named NIO1 (Negative-Ion Optimization 1), with 9 beam apertures for H~? extraction is under commissioning, in collaboration between Consorzio RFX and INFN, to provide a test bench for source optimizations, for innovations, and for simulation code validations in support of Neutral Beam Injectors (NBI) optimization. NIO1 installation includes a 60 kV high-voltage deck, power supplies for a 130mA ion nominal current, an X-ray shield, and beam diagnostics. Plasma is heated with a tunable 2MHz radiofrequency (rf) generator. Physical aspects of source operation and rf-plasma coupling are discussed. NIO1 tuning procedures and plasma experiments both with air and with hydrogen as filling gas are described, up to a 1.7 kW rf power. Transitions to inductively coupled plasma are reported in the case of air (for a rf power of about 0.5 kW and a gas pressure below 2Pa), discussing their robust signature in optical emission, and briefly summarized for hydrogen, where more than 1 kW rf power is needed.