Transient energetic charge exchange flux enhancement observed in NSTX neutral-beam-heated H-mode discharges
Abstract
Large increases in the E | | B Neutral Particle Analyzer (NPA) charge exchange neutral flux localized at the Neutral Beam Injection (NBI) full energy are observed in the National Spherical Torus Experiment (NSTX). Termed the High-Energy Feature (HEF), it appears only at the NBI full energy, exhibits growth times ~ 20-80 ms, seldom develops a slowing down distribution and arises only in discharges where NTM modes (f < 30 kHz) are absent, TAE activity (f ~ 30-150 kHz) is weak and GAE/CAE activity (f ~ 400-1200 kHz) is robust. The HEF occurs only in H-mode discharges with Pb >= 3 MW and v||/v ~ 0.7-0.9; i.e. only for passing ions. The HEF appears to be caused by a GAE wave-particle interaction that modifies of the NB fast ion distribution, fi(E,v||/v,r). This proposed mechanism was studied using the SPIRAL code that imports a TRANSP-calculated fi(E,v||/v,r) distribution and evolves it under drive from GAE wave-particle resonances.
Supported by U.S. DoE Contract Nos. DE-AC02-09CH11466, DE-FG02-99ER54527.- Publication:
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APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- October 2011
- Bibcode:
- 2011APS..DPPPP9058M