Physics of negative ions and helicon waves in a resonant antenna plasma source for neutral beams

-- Helicon sources for NBIs -- - Helicon plasmas as negative ion sources could have advantages over traditional ICPs: - 1) reduced RF power; - 2) stable operation at low pressure (< 0.3 Pa) resulting in low electron stripping losses; - 3) higher efficiency of negative ion production in volume production mode, and a high degree of molecular dissociation, which would be favorable in a caesiated source; - 4) by producing a magnetized plasma column, they are well-adapted to a blade-shape geometry, such as those required for photo-neutralizer-based NBIs. -- RAID [1] is a high-power (up to 20kW) helicon source equipped with resonant antennas [2]-- - Helicon plasmas in hydrogen and deuterium can be produced and sustained in steady-state; - RAID plasmas exhibit a negative ion-rich shell; - The maximum negative ion density increases with injected RF power; -- A 1.5 D fluid model coupled to experimental Te and ne profiles reproduces many observed features -- - Negative ions are generated by dissociative attachment on ro-vibrationally excited H2 molecules; - In the plasma column center, hot electrons destroy H- by electron detachment and mutual neutralization. At the edge of the plasma column, atomic detachment destroys H-; -- Extraction of negative ions -- - A radial extractor has been developed; - First experiments demonstrated negative ion extraction.