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Title: Characterization and performance of a field aligned ion cyclotron range of frequency antenna in Alcator C-Mod

Abstract

Ion cyclotron range of frequency (ICRF) heating is expected to provide auxiliary heating for ITER and future fusion reactors where high Z metallic plasma facing components (PFCs) are being considered. Impurity contamination linked to ICRF antenna operation remains a major challenge particularly for devices with high Z metallic PFCs. Here, we report on an experimental investigation to test whether a field aligned (FA) antenna can reduce impurity contamination and impurity sources. We compare the modification of the scrape of layer (SOL) plasma potential of the FA antenna to a conventional, toroidally aligned (TA) antenna, in order to explore the underlying physics governing impurity contamination linked to ICRF heating. The FA antenna is a 4-strap ICRF antenna where the current straps and antenna enclosure sides are perpendicular to the total magnetic field while the Faraday screen rods are parallel to the total magnetic field. In principle, alignment with respect to the total magnetic field minimizes integrated E|| (electric field along a magnetic field line) via symmetry. A finite element method RF antenna model coupled to a cold plasma model verifies that the integrated E|| should be reduced for all antenna phases. Monopole phasing in particular is expected to have the lowestmore » integrated E||. Consistent with expectations, we observed that the impurity contamination and impurity source at the FA antenna are reduced compared to the TA antenna. In both L and H-mode discharges, the radiated power is 20%–30% lower for a FA-antenna heated discharge than a discharge heated with the TA-antennas. However, inconsistent with expectations, we observe RF induced plasma potentials (via gas-puff imaging and emissive probes to be nearly identical for FA and TA antennas when operated in dipole phasing). Moreover, the highest levels of RF-induced plasma potentials are observed using monopole phasing with the FA antenna. Thus, while impurity contamination and sources are indeed reduced with the FA antenna configuration, the mechanism determining the SOL plasma potential in the presence of ICRF and its impact on impurity contamination and sources remains to be understood.« less

Authors:
; ; ; ; ; ; ; ; ; ; ;  [1]
  1. MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States)
Publication Date:
OSTI Identifier:
22228089
Resource Type:
Journal Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 20; Journal Issue: 5; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1070-664X
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALCATOR DEVICE; ANTENNAS; AUXILIARY HEATING; COLD PLASMA; COMPARATIVE EVALUATIONS; ELECTRIC FIELDS; FINITE ELEMENT METHOD; FIRST WALL; H-MODE PLASMA CONFINEMENT; ICR HEATING; ITER TOKAMAK; MAGNETIC FIELDS; PLASMA IMPURITIES; PLASMA POTENTIAL; PLASMA SCRAPE-OFF LAYER; PLASMA SIMULATION; PROBES; RF SYSTEMS; THERMONUCLEAR REACTOR MATERIALS

Citation Formats

Wukitch, S. J., Garrett, M. L., Ochoukov, R., Terry, J. L., Hubbard, A., Labombard, B., Lau, C., Lin, Y., Lipschultz, B., Miller, D., Reinke, M. L., Whyte, D., and Collaboration: Alcator C-Mod Team. Characterization and performance of a field aligned ion cyclotron range of frequency antenna in Alcator C-Mod. United States: N. p., 2013. Web. doi:10.1063/1.4803882.
Wukitch, S. J., Garrett, M. L., Ochoukov, R., Terry, J. L., Hubbard, A., Labombard, B., Lau, C., Lin, Y., Lipschultz, B., Miller, D., Reinke, M. L., Whyte, D., & Collaboration: Alcator C-Mod Team. Characterization and performance of a field aligned ion cyclotron range of frequency antenna in Alcator C-Mod. United States. doi:10.1063/1.4803882.
Wukitch, S. J., Garrett, M. L., Ochoukov, R., Terry, J. L., Hubbard, A., Labombard, B., Lau, C., Lin, Y., Lipschultz, B., Miller, D., Reinke, M. L., Whyte, D., and Collaboration: Alcator C-Mod Team. Wed . "Characterization and performance of a field aligned ion cyclotron range of frequency antenna in Alcator C-Mod". United States. doi:10.1063/1.4803882.
@article{osti_22228089,
title = {Characterization and performance of a field aligned ion cyclotron range of frequency antenna in Alcator C-Mod},
author = {Wukitch, S. J. and Garrett, M. L. and Ochoukov, R. and Terry, J. L. and Hubbard, A. and Labombard, B. and Lau, C. and Lin, Y. and Lipschultz, B. and Miller, D. and Reinke, M. L. and Whyte, D. and Collaboration: Alcator C-Mod Team},
abstractNote = {Ion cyclotron range of frequency (ICRF) heating is expected to provide auxiliary heating for ITER and future fusion reactors where high Z metallic plasma facing components (PFCs) are being considered. Impurity contamination linked to ICRF antenna operation remains a major challenge particularly for devices with high Z metallic PFCs. Here, we report on an experimental investigation to test whether a field aligned (FA) antenna can reduce impurity contamination and impurity sources. We compare the modification of the scrape of layer (SOL) plasma potential of the FA antenna to a conventional, toroidally aligned (TA) antenna, in order to explore the underlying physics governing impurity contamination linked to ICRF heating. The FA antenna is a 4-strap ICRF antenna where the current straps and antenna enclosure sides are perpendicular to the total magnetic field while the Faraday screen rods are parallel to the total magnetic field. In principle, alignment with respect to the total magnetic field minimizes integrated E|| (electric field along a magnetic field line) via symmetry. A finite element method RF antenna model coupled to a cold plasma model verifies that the integrated E|| should be reduced for all antenna phases. Monopole phasing in particular is expected to have the lowest integrated E||. Consistent with expectations, we observed that the impurity contamination and impurity source at the FA antenna are reduced compared to the TA antenna. In both L and H-mode discharges, the radiated power is 20%–30% lower for a FA-antenna heated discharge than a discharge heated with the TA-antennas. However, inconsistent with expectations, we observe RF induced plasma potentials (via gas-puff imaging and emissive probes to be nearly identical for FA and TA antennas when operated in dipole phasing). Moreover, the highest levels of RF-induced plasma potentials are observed using monopole phasing with the FA antenna. Thus, while impurity contamination and sources are indeed reduced with the FA antenna configuration, the mechanism determining the SOL plasma potential in the presence of ICRF and its impact on impurity contamination and sources remains to be understood.},
doi = {10.1063/1.4803882},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 5,
volume = 20,
place = {United States},
year = {2013},
month = {5}
}