Searching for Enhanced RF Field Amplitudes 
in the SOL Using a Simplified Cold-Plasma Model

Authors:   R.J. Perkins, J. C. Hosea, N. Bertelli, E.F. Jaeger, 
C. K. Phillips, G. Taylor, J. R. Wilson

Abstract:   NSTX uses a high-harmonic fast-wave (HHFW) antenna for plasma heating and current drive, but a significant amount of the HHFW can be lost along open magnetic fields lines in the SOL to the divertor regions under certain conditions [1,2]. The underlying cause is related to fast-wave propagation in the scrape-off layer (SOL), as the heating efficiency is strongly correlated with the location of the righthand cutoff. Recent results with the full-wave simulation AORSA suggest that the RF electric field amplitude grows to large values in the SOL when the SOL density is large enough that there is no cutoff region in front of the antenna [3]. However, interpretation of the AORSA results have not been straightforward due to the complicated vessel and magnetic geometry [4]. In this paper, we employ a cylindrical cold-plasma model to determine which features of the AORSA results can be reproduced in this simplified geometry. We do indeed find modes that conduct a significant fraction of power in a low density periphery plasma surrounding the dense core plasma, but more work is needed to quantitatively link these results to those from experiments and from AORSA.
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Presented at:  42nd European Physical Society (EPS) Conference on Plasma Physics, Lisbon, Portugal, June 2015
Published as:  Proceedings of 42nd EPS Conference on Plasma Physics
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Download PPPL-5147 (pdf 2.4 MB 7pp)
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