[Table of Contents]

Plasma and Fusion Research

Volume 2, S1109 (2007)

Regular Articles

Laser Scattering Measurement of the Electron Density Fluctuations in CHS
Yoshifumi AZUMA, Shunji TSUJI-IIO, Tsuyoshi AKIYAMA1), Kazuo KAWAHATA1), Shoichi OKAMURA1), Shigeki OKAJIMA2), Kazuya NAKAYAMA2), Ryuichi SHIMADA, Hiroaki TSUTSUI, Kenji HIGUCHI and CHS experimental group1)
Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
1)
National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
2)
Chubu University, Matsumoto-cho, Kasugai-shi, Aichi 487-8501, Japan
(Received 4 December 2006 / Accepted 21 May 2007 / Published 20 November 2007)

Abstract

For measurement of electron density fluctuations (up to 1 MHz), an HCN laser scattering measurement system with a super rotating grating was developed on CHS. When we measured electron density fluctuations with kr = 5.4 cm-1 in a plasma edge region at the outer side of torus, fluctuation spectra which have harmonic components up to the fifth were observed. The fundamental frequency was less than about 60 kHz, which changed during the discharge. The change in frequency correlated best with the plasma stored energy divided by the line averaged density. An edge transport barrier (ETB), which can improve particle transport in the edge region, has been observed in CHS and the measured fluctuation amplitude also decreases. The fluctuations decreased in about 5 ms, and the decrease of the fluctuations preceded by 3 ms to the drop of Hα emission signal.

Keywords

compact helical system, electron density fluctuation, laser scattering measurement, heterodyne technique, HCN laser, harmonic components of fluctuation spectra, ETB formation

DOI: 10.1585/pfr.2.S1109

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This paper may be cited as follows:

Yoshifumi AZUMA, Shunji TSUJI-IIO, Tsuyoshi AKIYAMA, Kazuo KAWAHATA, Shoichi OKAMURA, Shigeki OKAJIMA, Kazuya NAKAYAMA, Ryuichi SHIMADA, Hiroaki TSUTSUI, Kenji HIGUCHI and CHS experimental group, Plasma Fusion Res. 2, S1109 (2007).