9:45 AM–12:15 PM, Tuesday, November 18, 2008
- Landmark A
Chair: William Heidbrink, University of California, Irvine
Abstract ID: BAPS.2008.DPP.GI1.1
9:45 AM–10:15 AM
Mario Podesta
(UC Irvine)
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{\_}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 \textit{avalanches}. n{\_}f(R) decreases, but remains peaked at the magnetic axis. A depletion of the energy range $>$20keV, leading to drops of up to $\sim $20{\%} in the neutron rate over $<$500us, is observed. Good agreement is found between the radial profile and frequency of TAEs, measured by reflectometers and Mirnov coils, and the eigenmode structures calculated by the NOVA-k code. The latter are combined with the measured amplitude and frequency evolution to simulate the effect of TAEs on fast ion transport. Prompt fast-ion losses are also observed during EPMs. Slower time-scales ($\sim $10ms) are observed during CAE activity, which appears to be correlated with low-frequency kink modes. A depletion of the energy spectra above 20keV is observed for 100$<$R$<$130cm. Measurements of n{\_}f(R,t) by Fast-Ion D-Alpha (FIDA) spectroscopy are complemented by data from neutral particle analyzers, a scintillator-based fast-ion loss diagnostic and neutron detectors. Data are validated from studies of MHD quiescent discharges, and benchmarked against the results of simulation codes.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2008.DPP.GI1.1