ICRF-enhanced plasma potentials in the SOL of Alcator C-Mod

被引：39

作者：

Ochoukov, R. ^{[1
]}

Whyte, D. G. ^{[1
]}

Brunner, D. ^{[1
]}

D'Ippolito, D. A. ^{[2
]}

LaBombard, B. ^{[1
]}

Lipschultz, B. ^{[1
]}

Myra, J. R. ^{[2
]}

Terry, J. L. ^{[1
]}

Wukitch, S. J. ^{[1
]}

机构：

[1] PSFC MIT, Cambridge, MA 02139 USA

[2] Lodestar Res Corp, Boulder, CO 80301 USA

来源：

PLASMA PHYSICS AND CONTROLLED FUSION | 2014年 / 56卷 / 01期

关键词：

plasma potential; ICRF sheath rectification; Alcator C-Mod tokamak; FARADAY SCREEN; SHEATH; TRANSPORT; TOKAMAK; ANTENNA; VOLTAGE; WALL;

D O I：

10.1088/0741-3335/56/1/015004

中图分类号：

O35 [流体力学]; O53 [等离子体物理学];

学科分类号：

070204 ; 080103 ; 080704 ;

摘要：

An extensive experimental survey of plasma potentials induced by ion cyclotron range-of frequency (ICRF) heating was carried out in the scrape-off layer (SOL) plasmas on the Alcator C-Mod tokamak. Enhanced plasma potentials > 100V are observed at locations where local magnetic fields map to active ICRF antennas. In these cases, the enhanced potential appears only when a local plasma density threshold is surpassed-a threshold that is quantitatively consistent with slow wave (SW) RF rectification theory. However, in many cases large potential enhancements are found in locations that do not map along magnetic field lines to active antennas without obstruction, i.e. locations that are inaccessible to SWs launched by the active antennas. Enhanced potentials in these 'unmapped' locations are correlated with local plasma parameters, ICRF electromagnetic fields associated with the fast wave (FW) and SW, launched wave spectra, and the boundary surface geometry. It is found that enhanced plasma potentials in unmapped locations correlate with the FW field strength. These observations are qualitatively consistent with a model that accounts for the conversion of FWs to SWs at conducting surfaces oriented at an oblique angle with respect to the magnetic field, with the SW leading to sheath rectification. In addition, enhanced plasma potentials are found far into the shadow of passive limiter structures. These are correlated with the magnitude of the local FW field strength, yet the effect does not follow any present model. Overall, ICRF-induced plasma potentials may appear in regions far removed from the active antennas, yet due to the complex response of the SOL potentials at a variety of boundary surfaces, it remains unclear what part of the plasma-facing wall should be targeted to mitigate ICRF-induced impurities. The results also suggest that operating active ICRF antennas in a high single pass absorption regime is crucial in minimizing the effects of the FW fields on plasma-material interactions.

引用

页数：13

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