Plasma autobiasing during Ohmic H-mode in the STOR-M tokamak

Journal Article · Mon Nov 01 04:00:00 EST 1993 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860616· OSTI ID:5945293

Zhang, W; Xiao, C; Hirose, A ^[1]

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1. Plasma Physics Laboratory, Department of Physics, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 0W0 (Canada)

Application of a short current pulse on a nominal Ohmic discharge in the STOR-M tokamak (Saskatchewan Torus-Modified) [Phys. Fluids B [bold 4], 3277 (1992)] triggers the Ohmic H-mode characterized by reduced H[sub [alpha]] 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 ([le]20 kA, 100 [mu]sec) is shorter than the resistive skin time ([congruent]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.

• OSTI ID: 5945293
• Journal Information: Physics of Fluids B; (United States), Journal Name: Physics of Fluids B; (United States) Vol. 5:11; ISSN PFBPEI; ISSN 0899-8221
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700310* -- Plasma Confinement-- (1992-)
700340 -- Plasma Waves
Oscillations
& Instabilities-- (1992-)
CLOSED PLASMA DEVICES
CONFINEMENT
ELECTRODES
ELECTRON DENSITY
ELECTRON TEMPERATURE
FLUCTUATIONS
HEATING
PINCH EFFECT
PLASMA CONFINEMENT
PLASMA DIAGNOSTICS
PLASMA HEATING
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
VARIATIONS