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:

Muscatello, C. M.  ^[1];

• Search DOE PAGES for author "Muscatello, C. M."
• Search DOE PAGES for ORCID "0000-0003-3424-0419"

Heidbrink, W. W. ^[2]; Boivin, R. L. ^[1]; Chrystal, C.  ^[1];

• Search DOE PAGES for author "Chrystal, C."
• Search DOE PAGES for ORCID "0000-0003-3049-8658"

Collins, C. S. ^[1]; Fujiwara, Y. ^[3]; Yamaguchi, H. ^[3]

---

+ Show Author Affiliations

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:

Tue Jul 23 00:00:00 EDT 2019

Research Org.:

General Atomics, San Diego, CA (United States); Univ. of California, Irvine, CA (United States); National Inst. for Fusion Science (NIFS) (Japan)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1568811

Alternate Identifier(s):

OSTI ID: 1544449; OSTI ID: 1595475

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

Subject:

47 OTHER INSTRUMENTATION; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamak, fusion, magnetic confinement, energetic particles, fast ions, spectroscopy, neutral beam injection, fusion diagnostic