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Determination of the Major Impurity Radiators in the Reheat Mode Discharges in the Compact Helical System

Chihiro SUZUKI, Tsuyoshi AKIYAMA, Akihide FUJISAWA, Katsumi IDA, Mitsutaka ISOBE, Keisuke MATSUOKA, Takashi MINAMI, Kenichi NAGAOKA, Shin NISHIMURA, Shoichi OKAMURA, Byron J. PETERSON, Akihiro SHIMIZU, Chihiro TAKAHASHI, Kazuo TOI and Yasuo YOSHIMURA

National Institute for Fusion Science, Toki, Gifu 509-5292, Japan

(Received 4 December 2006 / Accepted 12 March 2007 / Published 20 November 2007)

Abstract

Radiation brightness and impurity behaviors have been studied for reheat mode discharges in the Compact Helical System (CHS) by three different types of impurity diagnostics. Total radiation power measured by a pyroelectric detector significantly reduces after entering the reheat mode, whereas the line-averaged radiation brightness measured by an absolute extreme ultraviolet (AXUV) photodiode array increases especially for a center viewing chord due to the impurity accumulation in the plasma core. One possible reason for this opposite behavior between the two bolometric detectors is the reduced sensitivity of the AXUV photodiode for lower energy photons in vacuum ultraviolet (VUV) region. This speculation is supported by temporal evolutions of VUV spectra measured by a grazing incidence spectrometer. These results demonstrate that the comparison of three impurity diagnostics would be beneficial to the determination of the major impurity radiators and a comprehensive understanding of impurity behaviors in the reheat mode discharges.

Copyright (c) 2007 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

CHS, reheat mode, impurity, bolometer, pyroelectric detector, AXUV photodiode, VUV spectrometer, spectral sensitivity

DOI: 10.1585/pfr.2.S1062

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This paper may be cited as follows:

Chihiro SUZUKI, Tsuyoshi AKIYAMA, Akihide FUJISAWA, Katsumi IDA, Mitsutaka ISOBE, Keisuke MATSUOKA, Takashi MINAMI, Kenichi NAGAOKA, Shin NISHIMURA, Shoichi OKAMURA, Byron J. PETERSON, Akihiro SHIMIZU, Chihiro TAKAHASHI, Kazuo TOI and Yasuo YOSHIMURA, Plasma Fusion Res. 2, S1062 (2007).