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Time Evolution of the Spatial Structure of the Radial Electric Field in the Tohoku University Heliac

Hiroshi AOYAMA, Sumio KITAJIMA, Mamiko SASAO, Atsushi OKAMOTO, Takashi KOBUCHI, Yutaka TANAKA, Hiroyasu UTOH, Hajime UMETSU, Keiichi ISHII and Hiromi TAKAHASHI¹⁾

Department of Quantum Science and Energy Engineering, Tohoku University, Sendai 980-8579, Japan

1)

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan

(Received 16 November 2007 / Accepted 17 March 2008 / Published 20 August 2008)

Abstract

Radial electric fields are closely related to the confinement of plasma. Electrode biasing experiments were conducted to actively control the radial electric field by ramping up/down the electrode current in the Tohoku University Heliac (TU-Heliac). An emissive probe array consisting of three filaments was designed as a new type of measurement equipment. Using this probe, time evolutions of the spatial structure of the radial electric field were measured in the biasing experiments. The radial electric field tended to extend from the inner region to the outer region, while ramping up the electrode current. In the plasma inner region, the radial electric field was maintained for a longer time than in the outer region, while ramping down the electrode current. The radial electric field, poloidal flow of plasma, and fluctuation level of the ion saturation current changed appreciably in the period when the electrode voltage showed negative resistance against the electrode current. Therefore, the period when the plasma shows negative resistance agreed with the transition region to the improved confinement mode.

Copyright (c) 2008 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

radial electric field, emissive probe, electrode biasing experiment, LH transition, fluctuation

DOI: 10.1585/pfr.3.S1026

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This paper may be cited as follows:

Hiroshi AOYAMA, Sumio KITAJIMA, Mamiko SASAO, Atsushi OKAMOTO, Takashi KOBUCHI, Yutaka TANAKA, Hiroyasu UTOH, Hajime UMETSU, Keiichi ISHII and Hiromi TAKAHASHI, Plasma Fusion Res. 3, S1026 (2008).