Commissioning and first results of the DIII-D helicon system

A 1 MW-level helicon launcher system at DIII-D is being commissioned to demonstrate efficient off-axis current drive in high- plasmas, where full single-pass absorption is expected. A 30-module traveling wave antenna of the comb-line type can be fed from either side to allow co- or counter- current drive. A klystron at 476 MHz has been commissioned into a test load at 1 MW forward power. During antenna conditioning ~0.3 MW of helicon power was coupled successfully to a highly reproducible L-mode target plasma, in quasi-steady RF pulses as long as 0.5 s. Clear conditioning progress was observed in repeated discharges. Several dedicated helicon diagnostics obtained data for the first time: Langmuir probes adjacent to the antenna observed changes to the SOL density; High-Frequency Ion Cyclotron Emissions (HICE) and Doppler Back Scattering (DBS) observed magnetic and density fluctuations near 476 MHz and nearby sidebands. Additional diagnostics to measure wave propagation and antenna-region density profiles will be installed this year.