Fast-wave Power Flow Along SOL Field Lines In NSTX nd The Associated Power Deposition Profile Across The SOL In Front Of The Antenna
Authors: Rory Perkins, et. al.
Abstract:
Fast-wave heating and current drive efficiencies can be reduced by a number of
processes in the vicinity of the antenna and in the scrape off layer (SOL). On NSTX from
around 25% to more than 60% of the high-harmonic fast-wave power can be lost to the SOL
regions, and a large part of this lost power flows along SOL magnetic field lines and is
deposited in bright spirals on the divertor floor and ceiling. We show that field-line mapping
matches the location of heat deposition on the lower divertor, albeit with a portion of the heat
outside of the predictions. The field-line mapping can then be used to partially reconstruct the
profile of lost fast-wave power at the midplane in front of the antenna, and the losses peak close
to the last closed flux surface (LCFS) as well as the antenna. This profile suggests a radial
standing-wave pattern formed by fast-wave propagation in the SOL, and this hypothesis will be
tested on NSTX-U. Advanced RF codes must reproduce these results so that such codes can be
used to understand this edge loss and to minimize RF heat deposition and erosion in the divertor
region on ITER.
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Submitted to: Nuclear Fusion (December 2012)
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Download PPPL-4918 (pdf 275 KB 10 pp)
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