| Autor: |
Muscatello CM; General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA., Heidbrink WW; Department of Physics and Astronomy, University of California-Irvine, Irvine, California 92697, USA., Boivin RL; General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA., Chrystal C; General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA., Collins CS; General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA., Fujiwara Y; National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan., Yamaguchi H; National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan. |
| Abstrakt: |
Negative-ion neutral-beam injection (NNBI) is an important source of heating and current drive for next-step fusion devices where the injected energy can range from hundreds of keV to 1 MeV. Few diagnostics are suitable for phase-space resolved measurements of fast ions with energy in excess of 100 keV. A study to assess the feasibility of fast-ion deuterium-alpha (FIDA) spectroscopy to diagnose high-energy ions produced by NNBI is presented. Case studies with the Large Helical Device (LHD) and JT-60SA illustrate possible solutions for the measurement. The distribution function of fast ions produced by NNBI is calculated for both devices, and the FIDA spectrum is predicted by synthetic diagnostic simulation. Results with 180 keV NNBI in LHD show that, with a judicious choice of viewing geometry, the FIDA intensity is comparable to that obtained with the existing FIDA system. The measurement is more challenging with the 500 keV NNBI in JT-60SA. Simulations predict the FIDA intensity to be about 1% of the background bremsstrahlung, which is small compared to existing FIDA implementations with positive neutral-beam injection where signal levels are an order of magnitude larger. The sampling time required to extract the small FIDA signal is determined using a probabilistic approach. Results indicate that long averaging periods, from ones to tens of seconds, are needed to resolve the FIDA signal in JT-60SA. These long averaging times are suitable in long-pulse (∼100 s), steady-state devices like JT-60SA where an important measurement objective is the spatial profile of the slowing-down distribution of fast ions. |
