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Title: The contribution of radio-frequency rectification to field-aligned losses of high-harmonic fast wave power to the divertor in the National Spherical Torus eXperiment

The National Spherical Torus eXperiment (NSTX) can exhibit a major loss of high-harmonic fast wave (HHFW) power along scrape-off layer (SOL) field lines passing in front of the antenna, resulting in bright and hot spirals on both the upper and lower divertor regions. One possible mechanism for this loss is RF sheaths forming at the divertors. Here, we demonstrate that swept-voltage Langmuir probe characteristics for probes under the spiral are shifted relative to those not under the spiral in a manner consistent with RF rectification. We estimate both the magnitude of the RF voltage across the sheath and the sheath heat flux transmission coefficient in the presence of the RF field. Although precise comparison between the computed heat flux and infrared (IR) thermography cannot yet be made, the computed heat deposition compares favorably with the projections from IR camera measurements. The RF sheath losses are significant and contribute substantially to the total SOL losses of HHFW power to the divertor for the cases studied. This work will guide future experimentation on NSTX-U, where a wide-angle IR camera and a dedicated set of coaxial Langmuir probes for measuring the RF sheath voltage directly will quantify the contribution of RF sheath rectificationmore » to the heat deposition from the SOL to the divertor.« less
Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;  [1] ; ;  [2] ;  [3] ;  [4]
  1. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
  2. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
  3. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
  4. Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)
Publication Date:
OSTI Identifier:
22408315
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 4; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANTENNAS; CAMERAS; DIVERTORS; ELECTRIC POTENTIAL; HEAT FLUX; INFRARED SURVEYS; LANGMUIR PROBE; NSTX DEVICE; PLASMA SCRAPE-OFF LAYER; RADIOWAVE RADIATION; THERMOGRAPHY; WAVE POWER