Validating predictive models for fast ion profile 
relaxation in burning plasmas

Authors:  N. N. Gorelenkov, W. W. Heidbrink, G.J. Kramer, 
J.B. Lestz, M. Podesta, M. A. Van Zeeland, R. B. White

Abstract:  The redistribution and potential loss of energetic particles due to MHD modes can limit the performance of fusion plasmas by reducing the plasma heating rate. In this work, we present validation studies of the 1.5D Critical Gradient Model (CGM) for Alfven eigenmode induced EP transport in NSTX and DIII-D neutral beam heated plasmas. In previous comparisons with a single DIII-D L-mode case, the CGM model was found to be in surprisingly good agreement with measured AE induced neutron deficits [1]. A fully kinetic HINST is used to compute mode stability for the non-perturbative version of CGM (or nCGM). We have found that AEs show strong local instability drive up to
/ ∼ 20% violating assumptions of perturbative approaches used in NOVA-K code. We demonstrate that both models agree with each other and both underestimate the neutron deficit measured in DIII-D shot by approximately a factor of 2.  On the other hand in NSTX the application of CGM shows good agreement for the measured flux deficit predictions. We attempt to understand these results with the help of the so-called kick model which is based on the guiding center code ORBIT. The kick model comparison gives important insight into the underlying velocity space dependence of the AE induced EP transport as well as it allows the estimate of the neutron deficit in the presence of the low frequency Alfvenic modes.
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Submitted to:  Nuclear Fusion
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Download PPPL-5227 (pdf 2.2 MB 22 pp)
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