Helicon Volume Production of H- and D- Using a Resonant Birdcage Antenna on RAID

Negative ion production by volumetric processes is investigated in the RAID linear device using experiments and modeling. Measurements by optical emission spectroscopy, cavity ring-down spectroscopy, and Langmuir probe assisted laser photodetachment are combined and reveal that H- and D- ions are distributed in a halo around the plasma column with densities of 2 × 1016 m-3 for only a few kilowatts of RF power in a Cs-free plasma. A hydrogen transport fluid code shows that RAID plasmas have a hot electron core favorable to ro-vibrational excitation and dissociation of H2 molecules. Dissociative attachment to ro-vibrationally excited H2 molecules is the only significant source of H- anywhere in the RAID volume.