Plasma autobiasing during Ohmic H‐mode in the STOR‐M tokamak
作者:
W. Zhang,
C. Xiao,
A. Hirose,
期刊:
Physics of Fluids B: Plasma Physics
(AIP Available online 1993)
卷期:
Volume 5,
issue 11
页码: 3961-3968
ISSN:0899-8221
年代: 1993
DOI:10.1063/1.860616
出版商: AIP
数据来源: AIP
摘要:
Application of a short current pulse on a nominal Ohmic discharge in the STOR‐M tokamak (Saskatchewan Torus‐Modified) [Phys. Fluids B4, 3277 (1992)] triggers the Ohmic H‐mode characterized by reduced H&agr;radiation, increased electron density, and reduced edge density/magnetic fluctuations. Measurements of plasma floating potential at the plasma edge and in the scrape‐off layer indicate that the Ohmic H‐mode is accompanied by negative plasma autobiasing, which leads to a steeper radial electric field profile at the edge. Since the duration of the current pulse (≤20 kA, 100 &mgr;sec) is shorter than the resistive skin time (&bartil;1 msec), preferential edge heating is expected, which is believed to be responsible for changes in the edge discharge condition favorable for inducing the Ohmic H‐mode. The electron density profile becomes steeper at the edge during the H‐mode, and clear formation of a density pedestal has been seen. The evolution of the density profile suggests the presence of particle pinch. An improved confinement phase (ICP) is induced by external negative electrode biasing. The ICP reveals some similarities as compared to the current pulse induced H‐mode. It is found that the electrostatic modes are dominant in the scrape‐off layer while electromagnetic modes dominate in the plasma edge during the normal Ohmic discharges.
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