Physics – Plasma Physics
Scientific paper
Nov 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aps..dppgi1001p&link_type=abstract
American Physical Society, 50th Annual Meeting of the Division of Plasma Physics, November 17-21, 2008, abstract #GI1.001
Physics
Plasma Physics
Scientific paper
Interaction of fast ions with Alfv'{e}n eigenmodes (AEs) may redistribute fast ions in phase and real space, and degrade fusion and current drive efficiencies in devices such as ITER. A plethora of AEs naturally occurs in beam-heated NSTX plasmas, making it a suitable environment for fast-ion studies. Space and energy resolved measurements of fast-ion dynamics during AE activity are presented. The effects of toroidicity-induced AEs (TAE), energetic-particle modes (EPM) and compressional AEs (CAE) are discussed. Modest changes in the fast-ion profile, n&_slash;f(R), correlate with TAEs for multiple, non-interacting modes. As the beam beta is increased above a critical threshold, TAEs interact non-linearly and disrupt in {avalanches}. n&_slash;f(R) decreases, but remains peaked at the magnetic axis. A depletion of the energy range >20keV, leading to drops of up to ˜ 20&%slash; in the neutron rate over <500us, is observed. Good agreement is found between the radial profile and frequency of TAEs, measured by reflectometers and Mirnov coils, and the eigenmode structures calculated by the NOVA-k code. The latter are combined with the measured amplitude and frequency evolution to simulate the effect of TAEs on fast ion transport. Prompt fast-ion losses are also observed during EPMs. Slower time-scales ( ˜ 10ms) are observed during CAE activity, which appears to be correlated with low-frequency kink modes. A depletion of the energy spectra above 20keV is observed for 100
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