Fast-ion Energy Loss During TAE Avalanches in the National Spherical Torus Experiment
Authors: E.D. Fredrickson, N.A. Crocker, D.S. Darrow, N.N. Gorelenkov, G.J. Kramer, S. Kubota, M. Podesta, R.B. White, A. Bortolon, S.P. Gerhardt, R.E. Bell, A. Diallo, B. LeBlanc, F.M. Levinton, H. Yuh
Abstract: Strong TAE avalanches on NSTX, the National Spherical Torus Experiment
[M. Ono, et al., Nucl. Fusion 40 (2000) 557] are typically correlated with
drops in the neutron rate in the range of 5% - 15%. In previous studies of
avalanches in L-mode plasmas, these neutron drops were found to be
consistent with modeled losses of fast ions. Here we expand the study to TAE
avalanches in NSTX H-mode plasmas with improved analysis techniques. At
the measured TAE mode amplitudes, simulations with the ORBIT code predict
that fast ion losses are negligible. However, the simulations predict that the
TAE scatter the fast ions in energy, resulting in a small (≈ 6%) drop in fast ion
β. The net decrease in energy of the fast ions is sufficient to account for the
bulk of the drop in neutron rate, even in the absence of fast ion losses. This
loss of energy from the fast ion population is comparable to the estimated
energy lost by damping from the Alfven wave during the burst. The
previously studied TAE avalanches in L-mode are re-evaluated using an
improved calculation of the potential fluctuations in the ORBIT code.
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2013 Nucl. Fusion 53 013006 doi:10.1088/0029-5515/53/1/013006
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