Predictions of VRF on a Langmuir Probe under the RF Heating Spiral on the Divertor Floor on NSTX-U
Authors: J.C. Hosea, R.J. Perkins, M.A. Jaworski, G.J. Kramer, J-W Ahn, et al.
Abstract: RF heating deposition spirals are observed on the divertor plates on NSTX as shown in for a NB plus RF heating case. It has been shown that the RF spiral is tracked quite well by the spiral mapping of the strike points on the divertor plate of magnetic field lines passing in front of the high harmonic fast wave (HHFW) antenna on NSTX. Indeed, both current instrumented tiles and Langmuir probes respond to the spiral when it is positioned over them. In particular, a positive increment in tile current (collection of electrons) is obtained when the spiral is over the tile. This current can be due to RF rectification and/or RF heating of the scrape off layer (SOL) plasma along the magnetic field lines passing in front of the the HHFW antenna. It is important to determine quantitatively the relative contributions of these processes. Here we explore the properties of the characteristics of probes on the lower divertor plate to determine the likelyhood that the primary cause of the RF heat deposition is RF rectification.
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Presented at: 41st European Physical Society (EPS) Conference on Plasma Physics, Berlin, June 23 27, 2014.
Published on-line in conference procedings: http://ocs.ciemat.es/EPS2014PAP/html/
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Download PPPL-5036 (pdf 8.4 MB 4pp)
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