Recent Studies of Hydrogen Negativ e Ion Source and Beam Production for NBI in Large Helical Device

Neutral beam injector (NBI) is an indispensable device to produce high-density and hot plasmas in fusion development machine. We have developed negative-ion-based NBI (N- NBI) in LHD, that have been operated continuously since 1998. Three N-NBIs are arranged tangentially, and was equipped with a negative hydrogen ion (H-) source which enabled high energy and high power beam injection. The nominal specication of beam energy and beam power for each N-NBI was 180 keV and 5 MW, respectively. We had achieved 16 MW beam injection by three N-NBIs in LHD experiment. Moreover, we installed two positive-ion-based neutral beam injector (P-NBI) arranged perpendicularly to the LHD. High-power (12 MW) with lower energy (40~60 keV) beam injection allowed effective ion heating and profile measurement of ion temperature by charge exchange recombination spectroscopy. A hydrogen negative ion source is a key component in N-NBI system, that will also use future NBI in ITER. Understanding of H- behavior from cesiated metal production surface to extraction aperture is an important issue to maintain high power negative ion beam. We have researched distribution of H- ions and its extraction behavior by cavity ring-down spectroscopy and a spectrally-selective imaging system, respectively, in the 1/3 scaled ion source (NIFS-RNIS). We found that H- ions widely distributed in the extraction region, and these ions constituted H- beam. Recently, we have a lot of domestic and international collaboration program for H- source. We applied a spectrally-selective imaging system in RF hydrogen negative on source in ELISE test facility in Max-Planck-Institut fur Plasmaphysik (IPP) Garching (Germany). We found clear signal response on H? emission during beam extraction. This observation will contribute to obtain behavior of H- ions in RF source which is variable output for production high power beam and optimization of beam shape in ITER source. We also observed an extracted H- beam shape in NIFS-RNIS used the mini-STRIKE system which consists of a carbon- fibre-carbon-composite (CFC) tiles and an infrared camera collaborated with Consorzio RFX (Italy). We found the clear dependence between the beam shape and operating parameters. These findings have contributed to the high performance and safety NBI operation in the LHD.