Physics of Negative Ions and Helicon Waves in a Resonant Antenna Plasma Source for Neutral Beams

Present activities on the Resonant Antenna Ion Device (RAID) [1] at the Swiss Plasma Center aim at broadening the current knowledge of volume production of negative ions as well as the physics of helicon wave propagation in hydrogen and deuterium plasmas for neutral beam injectors (NBIs) for fusion. In RAID, H2/D2 plasmas are produced and sustained using a steady-state, 10 kW birdcage resonant network at 13.56 MHz with typical electron densities ne?1018 m-3 and temperatures Te?5 eV. We demonstrate the existence of an edge plasma region where H-/D- ions are produced by dissociative attachment with significant absolute densities and in volume production mode with a few kW RF power, without using cesium, and at 0.3 Pa, as required by NBIs to minimize stripping losses. Furthermore, we provide first measurements of the wave-field of the helicon wave, which determines the wave power deposition. Combining the full set of plasma and helicon wave diagnostics with numerical modeling, we approach a level where quantitative comparison between theory and experiments is possible. These results are promising for the application of helicon plasmas as sources of negative ions for future NBIs.