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Title: Diagnosis of fast ions produced by negative-ion neutral-beam injection with fast-ion deuterium-alpha spectroscopy

Abstract

Negative neutral-beam injection (NNBI) is an important source of heating and current drive for next-step devices like JT-60SA and ITER 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 feasibility study of using fast-ion deuterium-alpha (FIDA) spectroscopy to diagnose the high-energy ions produced by NNBI in a fusion plasma is presented. Two case studies with the Large Helical Device (LHD) and JT-60SA illustrate possible solutions for the measurement. The steady-state slowing-down 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 typical time resolution of ~10 ms achieved with existing FIDA systems can be obtained with NNBI FIDA on LHD. The measurement is more challenging with the 500-keV NNBI in JT-60SA. In this case, simulations predict the FIDA intensity to be about 1% of the background bremsstrahlung, which is small compared to existing FIDA implementationsmore » 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, depending on the FIDA and background variance, are needed to resolve the FIDA signal in JT-60SA. These long averaging times are suitable in long-pulse (~ 100s), steady-state devices like JT-60SA where an important measurement objective is the spatial profile of the slowing-down distribution of fast ions.« less

Authors:
ORCiD logo [1];  [2];  [1]; ORCiD logo [1];  [1];  [3];  [3]
  1. General Atomics, San Diego, CA (United States)
  2. Univ. of California-Irvine, Irvine, CA (United States). Dept. of Physics and Astronomy
  3. National Inst. for Fusion Science, Toki, Gifu (Japan)
Publication Date:
Research Org.:
U.S. Dept. of Energy (USDOE), Washington D.C. (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1568811
Alternate Identifier(s):
OSTI ID: 1544449
Grant/Contract Number:  
FC02-04ER54698; SC0018107
Resource Type:
Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 90; Journal Issue: 7; Journal ID: ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English

Citation Formats

Muscatello, C. M., Heidbrink, W. W., Boivin, R. L., Chrystal, C., Collins, C. S., Fujiwara, Y., and Yamaguchi, H. Diagnosis of fast ions produced by negative-ion neutral-beam injection with fast-ion deuterium-alpha spectroscopy. United States: N. p., 2019. Web. doi:10.1063/1.5099491.
Muscatello, C. M., Heidbrink, W. W., Boivin, R. L., Chrystal, C., Collins, C. S., Fujiwara, Y., & Yamaguchi, H. Diagnosis of fast ions produced by negative-ion neutral-beam injection with fast-ion deuterium-alpha spectroscopy. United States. doi:10.1063/1.5099491.
Muscatello, C. M., Heidbrink, W. W., Boivin, R. L., Chrystal, C., Collins, C. S., Fujiwara, Y., and Yamaguchi, H. Tue . "Diagnosis of fast ions produced by negative-ion neutral-beam injection with fast-ion deuterium-alpha spectroscopy". United States. doi:10.1063/1.5099491.
@article{osti_1568811,
title = {Diagnosis of fast ions produced by negative-ion neutral-beam injection with fast-ion deuterium-alpha spectroscopy},
author = {Muscatello, C. M. and Heidbrink, W. W. and Boivin, R. L. and Chrystal, C. and Collins, C. S. and Fujiwara, Y. and Yamaguchi, H.},
abstractNote = {Negative neutral-beam injection (NNBI) is an important source of heating and current drive for next-step devices like JT-60SA and ITER 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 feasibility study of using fast-ion deuterium-alpha (FIDA) spectroscopy to diagnose the high-energy ions produced by NNBI in a fusion plasma is presented. Two case studies with the Large Helical Device (LHD) and JT-60SA illustrate possible solutions for the measurement. The steady-state slowing-down 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 typical time resolution of ~10 ms achieved with existing FIDA systems can be obtained with NNBI FIDA on LHD. The measurement is more challenging with the 500-keV NNBI in JT-60SA. In this case, 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, depending on the FIDA and background variance, are needed to resolve the FIDA signal in JT-60SA. These long averaging times are suitable in long-pulse (~ 100s), steady-state devices like JT-60SA where an important measurement objective is the spatial profile of the slowing-down distribution of fast ions.},
doi = {10.1063/1.5099491},
journal = {Review of Scientific Instruments},
number = 7,
volume = 90,
place = {United States},
year = {2019},
month = {7}
}

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This content will become publicly available on July 23, 2020
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