[Table of Contents]

Plasma and Fusion Research

Volume 5, S2077 (2010)

Regular Articles

Measurement of Blob-Like Structures in Plasma with a Langmuir Probe and Fast Camera on QUEST
Haiqing LIU, Kazuaki HANADA1), Nobuhiro NISHINO2), Ryota OGATA, Masaki ISHIGURO, Hideki ZUSHI1), Kazuo NAKAMURA1), Mizuki SAKAMOTO1), Hiroshi IDEI1), Makoto HASEGAWA1), Yuta HIGASHIZONO1), Shoji KAWASAKI1), Hisatoshi NAKASHIMA1), Aki HIGASHIJIMA1) and QUEST GROUP
IGSES, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan
1)
RIAM, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan
2)
Department of Mechanical System Engineering, Graduate School of Engineering, Hiroshima University, Japan
(Received 9 December 2009 / Accepted 9 April 2010 / Published 10 December 2010)

Abstract

This paper presents a scheme for combining a Langmuir probe with a fast camera for measurement of the behavior of blob-like structures in the boundary region of an electron cyclotron resonance (ECR) heating plasma in Q-shu University Experiment with a Steady-State Spherical Tokamak (QUEST, major radius, R = 0.68 m, minor radius, a = 0.40 m, and toroidal magnetic field, Bt = 0.25 T at R = 0.64 m). The frame rate of the camera was typically set to 40,000 frames per second (FPS) with 192 × 144 pixels per frame. Radial motion of blob-like structures was observed in the half of the plasma space where the probe head was located. A radially movable and rotatable probe system was used to measure the floating potential from single unbiased tips, the potential of the positively biased tip, and the ion saturation current in two orthogonal directions in the outboard midplane region. Time series of the ion saturation current measured by the Langmuir probe and of pixels in a 40,000 FPS movie were compared and cross-correlated. The results of the two diagnostics agreed well, and the spatial scale was found to be of the same as the size of the probe head. The ion saturation current was asymmetric in terms of the time the blob-like structure was passing; fast camera imaging also clearly demonstrated the blobs' filamentary structures and radial motion at the edge of QUEST. This means that plasma in the blob-like structure hunches over, like blobs in other devices. The typical radial velocity of the structures is ∼1 km/s, and the structures were accelerated along their path of radial motion from the inner to the outer parts of the vacuum vessel.

Keywords

fast camera, Langmuir probe, combined, blob-like structure, QUEST

DOI: 10.1585/pfr.5.S2077

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This paper may be cited as follows:

Haiqing LIU, Kazuaki HANADA, Nobuhiro NISHINO, Ryota OGATA, Masaki ISHIGURO, Hideki ZUSHI, Kazuo NAKAMURA, Mizuki SAKAMOTO, Hiroshi IDEI, Makoto HASEGAWA, Yuta HIGASHIZONO, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA and QUEST GROUP, Plasma Fusion Res. 5, S2077 (2010).