Diagnosing hydrogen plasma in a high power helicon device

Neutral Beam Injector systems (NBIs) will provide beam energies up to 1 MeV as part of the heating systems required for future fusion reactors. Positive ion neutralisation efficiency becomes prohibitively low above 100 keV whereas negative ions are capable of maintaining nearly 60% efficiency up to 1 MeV. RF Inductively Coupled Plasmas (ICPs) with powers up to 100 KW are currently used to generate high atomic and positive ion flux onto ceasiated surfaces to achieve sufficient negative ion densities. Helicon Coupled Plasmas (HCPs) can generate comparable plasma densities at lower applied power, however, few studies on HCPs have been conducted at low pressures less than 10 mTorr and high powers greater than a few kW for application as NBI sources. In this study we characterise a high-power HCP operating with hydrogen up to 20 kW between 2.5 and 10 mTorr in the MAGPIE device at the Australian National University. This includes power coupling measurements, electron densities and temperatures, atomic and molecular temperatures in the source and diverging magnetic field regions. Compared with the inductive mode, higher plasma densities and dissociation fractions are observed when operating in the helicon mode. Experimental measurements are compared with results from a 0-dimensional model.