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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

Abstract

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. 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. Though the precise comparison between 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. Our 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 rectification tomore » the heat deposition from the SOL to the divertor.« less

Authors:
 [1];  [1];  [1];  [2];  [1];  [1];  [1];  [1];  [2];  [1];  [1];  [3];  [1];  [1];  [1];  [4]; ORCiD logo [1]; ORCiD logo [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Columbia Univ., New York, NY (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1279419
Alternate Identifier(s):
OSTI ID: 1228291
Grant/Contract Number:
AC05-00OR22725; AC02-09CH11466
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 22; Journal Issue: 4; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Perkins, R. J., Hosea, J. C., Jaworski, M. A., Ahn, J. -W., Diallo, A., Bell, R. E., Bertelli, N., Gerhardt, S., Gray, T. K., Kramer, G. J., LeBlanc, B. P., McLean, A., Phillips, C. K., Podestà, M., Roquemore, L., Sabbagh, S., Taylor, G., and Wilson, J. R. 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. United States: N. p., 2015. Web. doi:10.1063/1.4916034.
Perkins, R. J., Hosea, J. C., Jaworski, M. A., Ahn, J. -W., Diallo, A., Bell, R. E., Bertelli, N., Gerhardt, S., Gray, T. K., Kramer, G. J., LeBlanc, B. P., McLean, A., Phillips, C. K., Podestà, M., Roquemore, L., Sabbagh, S., Taylor, G., & Wilson, J. R. 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. United States. doi:10.1063/1.4916034.
Perkins, R. J., Hosea, J. C., Jaworski, M. A., Ahn, J. -W., Diallo, A., Bell, R. E., Bertelli, N., Gerhardt, S., Gray, T. K., Kramer, G. J., LeBlanc, B. P., McLean, A., Phillips, C. K., Podestà, M., Roquemore, L., Sabbagh, S., Taylor, G., and Wilson, J. R. Mon . "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". United States. doi:10.1063/1.4916034. https://www.osti.gov/servlets/purl/1279419.
@article{osti_1279419,
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},
author = {Perkins, R. J. and Hosea, J. C. and Jaworski, M. A. and Ahn, J. -W. and Diallo, A. and Bell, R. E. and Bertelli, N. and Gerhardt, S. and Gray, T. K. and Kramer, G. J. and LeBlanc, B. P. and McLean, A. and Phillips, C. K. and Podestà, M. and Roquemore, L. and Sabbagh, S. and Taylor, G. and Wilson, J. R.},
abstractNote = {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. 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. Though the precise comparison between 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. Our 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 rectification to the heat deposition from the SOL to the divertor.},
doi = {10.1063/1.4916034},
journal = {Physics of Plasmas},
number = 4,
volume = 22,
place = {United States},
year = {Mon Apr 13 00:00:00 EDT 2015},
month = {Mon Apr 13 00:00:00 EDT 2015}
}

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