Abstract
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.
| Original language | English |
|---|---|
| Article number | 073504 |
| Journal | Review of Scientific Instruments |
| Volume | 90 |
| Issue number | 7 |
| DOIs | |
| State | Published - Jul 1 2019 |
| Externally published | Yes |
Funding
The authors gratefully acknowledge the JT-60SA Integrated Project Team and LHD Experiment Group for data exchange and fruitful discussions. This research was supported by the NINS program of Promoting Research by Networking among Institutions (Grant No. 01411702), the NIFS International Collaboration Research programs (Grant Nos. NIFS18/KLPR047 and NIFS07/KLPH004), and the LHD project budget (Nos. ULRR006, ULRR035, ULRR036, and ULRR702). A part of this work was performed on “Plasma Simulator” (No. FUJITSU FX100) of NIFS with the support and under the auspices of the NIFS Collaboration Research program Grant No. NIFS18KNST135. This material is also based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award Nos. DE-SC0018107 and DE-FC02-04ER54698. The authors gratefully acknowledge the JT-60SA Integrated Project Team and LHD Experiment Group for data exchange and fruitful discussions. This research was supported by the NINS program of Promoting Research by Networking among Institutions (Grant No. 01411702), the NIFS International Collaboration Research programs (Grant Nos. NIFS18/KLPR047 and NIFS07/KLPH004), and the LHD project budget (Nos. ULRR006, ULRR035, ULRR036, and ULRR702). A part of this work was performed on Plasma Simulator (No. FUJITSU FX100) of NIFS with the support and under the auspices of the NIFS Collaboration Research program Grant No. NIFS18KNST135. This material is also based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award Nos. DE-SC0018107 and DE-FC02-04ER54698.
