PPPL-4827
Perturbative Study of Energetic Particle Redistribution by Alfven Eigenmodes in ITER
Authors: N.N. Gorelenkov and R.B. White
Abstract:
The modification of particle distributions by magnetohydrodynamic modes is an important topic
for magnetically confined plasmas. Low amplitude modes are known to be capable of producing
significant modification of injected neutral beam profiles. Flattening of a distribution due to phase
mixing in an island or due to portions of phase space becoming stochastic is a process extremely
rapid on the time scale of an experiment. In this paper we examine the effect of toroidal Alfven
eigenmodes (TAE) and reversed shear Alfven eigenmodes (RSAE) in ITER on alpha particle and
injected beam distributions using theoretically predicted mode amplitudes. It is found that for the
equilibrium of a hybrid scenario even at ten times the predicted saturation level the modes have
negligible effect on these distributions. A strongly reversed shear (or advanced) scenario, having a
spectrum of modes that are much more global, is somewhat more susceptible to induced loss due
to mode resonance, with alpha particle losses of over one percent with predicted amplitudes and
somewhat larger with the assistance of toroidal field ripple. The elevated q profile contributes to
stronger TAE (RSAE) drive and more unstable modes. An analysis of the existing mode-particle
resonances is carried out to determine which modes are responsible for the profile modification
and induced loss. We find that losses are entirely due to resonance with the counter-moving and
trapped particle populations, with co-moving passing particles participating in resonances only
deep within the plasma and not leading to loss.
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Submitted to: Plasma Physics and Controlled Fusion (October 2012)
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Download PPPL-4827 (pdf 2.50 MB 17 pp)
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