Plasma and Fusion Research

Volume 1, 032 (2006)

Regular Articles

Study of Edge Transport Barrier Formation on CHS Plasma

Takashi MINAMI, Shoichi OKAMURA, Tsuyoshi AKIYAMA, Mitsutaka ISOBE, Tetsutaro OHISHI¹⁾, Haruhisa NAKANO²⁾, Katsumi IDA, Akihide FUJISAWA, Kiichiro NAKAMURA, Kenichi NAGAOKA, Mikiro YOSHINUMA, Chihiro SUZUKI, Yasuo YOSHIMURA, Kazuo TOI, Masaki NISHIURA, Shinsuke OHSHIMA³⁾, Zenzo NARUHIRO, Harukazu IGUCHI, Shin NISHIMURA, Akihiro SHIMIZU, Keisuke MATSUOKA and Chihiro TAKAHASHI

National Institute for Fusion Science
1): Department of Quantum Engineering and System Science, Tokyo University
2): Department of Fusion Science, The Graduate University for Advanced Studies
3): Department of Energy Engineering and Science, Nagoya University

(Received 16 June 2005 / Accepted 20 April 2006 / Published 22 June 2006)

Abstract

An edge transport barrier (ETB) similar to the tokamak H-mode has been observed for beam-heated plasma with two co-injected Neutral Beam Injectors (NBIs) in CHS. The Hα emission showed a clear spontaneous drop followed by an increase of line-averaged electron density at the L-H transition. Stored energy increased by ˜ 40% with H-factor improvement up to ˜ 30% compared to the international stellarator scaling (ISS04v03). A rapid density increase in the edge region to two-times level of the L-mode was observed to accompany a ˜ 15% increase in the density gradient. An ETB was formed when the plasma density exceeded the lower density limit by ˜ 1.5 × 10¹³ cm^-3 and the total NBI power exceeds the threshold level (P_deposit / n_e ˜ 200 × 10^-13 kW/cm^-3 at B_T = 0.95 T, R_ax = 92.1 cm, where P_deposit is the deposited NBI power, n_e is electron density, B_T is troidal magnetic field strength and R_ax is location of magnetic axis). The power threshold increased with the magnetic field strength, as in tokamak scaling, and depends on the magnetic field configuration of the helical plasma.

Keywords

edge transport barrier, helical plasma, H-mode, plasma confinement, improved confinement, threshold power, H-mode scaling, CHS

DOI: 10.1585/pfr.1.032

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This paper may be cited as follows:

Takashi MINAMI, Shoichi OKAMURA, Tsuyoshi AKIYAMA, Mitsutaka ISOBE, Tetsutaro OHISHI, Haruhisa NAKANO, Katsumi IDA, Akihide FUJISAWA, Kiichiro NAKAMURA, Kenichi NAGAOKA, Mikiro YOSHINUMA, Chihiro SUZUKI, Yasuo YOSHIMURA, Kazuo TOI, Masaki NISHIURA, Shinsuke OHSHIMA, Zenzo NARUHIRO, Harukazu IGUCHI, Shin NISHIMURA, Akihiro SHIMIZU, Keisuke MATSUOKA and Chihiro TAKAHASHI, Plasma Fusion Res. 1, 032 (2006).