Plasma and Fusion Research

Volume 3, S1071 (2008)

Regular Articles

Measurements of Micro-Turbulence in High Beta and High Density Regimes of LHD and Comparison with Resistive G-Mode Scaling

Clive MICHAEL, Kenji TANAKA, Leonid VYACHESLAVOV¹⁾, Andrei SANIN¹⁾, Tsuyoshi AKIYAMA, Yoshiro NARUSHIMA, Kiyomasa WATANABE, Hisamichi FUNABA, Sadayoshi MURAKAMI²⁾, Katsumi IDA, Mikiro YOSHINUMA, Ryuichi SAKAMOTO, Kazuo KAWAHATA and Shigeki OKAJIMA³⁾

National Institute of Fusion Science, Toki 509-5292, Japan
1): Budker Institute for Nuclear Physics, Novisibirsk, Russia
2): Department of Nuclear Engineering, Kyoto University, Kyoto 606-8501, Japan
3): Chubu University, Kasugai 487-8501, Japan

(Received 7 December 2007 / Accepted 11 March 2008 / Published 20 August 2008)

Abstract

Density fluctuations are analyzed in high volume average beta and high core density discharges in the Large Helical Device (LHD) using a 2D phase contrast imaging system and far infra-red interferometer. Both these regimes share similarly high beta gradients and evidence of pressure driven MHD modes is presented. In high volume average beta plasmas, both large and ion-gyro scale density fluctuation levels increase with beta and, in the edge, compare favorably with growth rate of resistive interchange modes, showing additional dependence on density at fixed β. In high core density plasmas with internal diffusion barrier, intermittent fluctuation bursts around mid radius are observed which are triggered when the normalized density gradient exceeds a certain threshold. The intermittent character is stronger for outward shifted plasmas and there appears to be a fluctuation suppression mechanism, possibly related to temperature gradient.

Keywords

high beta, density fluctuation, phase contrast imaging, MHD, resistive interchange, super dense core regime, ion temperature gradient turbulence

DOI: 10.1585/pfr.3.S1071

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This paper may be cited as follows:

Clive MICHAEL, Kenji TANAKA, Leonid VYACHESLAVOV, Andrei SANIN, Tsuyoshi AKIYAMA, Yoshiro NARUSHIMA, Kiyomasa WATANABE, Hisamichi FUNABA, Sadayoshi MURAKAMI, Katsumi IDA, Mikiro YOSHINUMA, Ryuichi SAKAMOTO, Kazuo KAWAHATA and Shigeki OKAJIMA, Plasma Fusion Res. 3, S1071 (2008).