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Title:
Validating modeling assumptions of alpha particles in electrostatic turbulence
Authors:
Wilkie, G. J.; Abel, I. G.; Highcock, E. G.; Dorland, W.
Affiliation:
AA(University of Maryland, College Park, MD 20742, USA), AB(Princeton University, Princeton, NJ 08544, USA), AC(University of Oxford, Oxford OX1 3NP, UK), AD(University of Maryland, College Park, MD 20742, USA)
Publication:
Journal of Plasma Physics, Volume 81, Issue 3, article id. 905810306, 24 pp.
Publication Date:
06/2015
Origin:
CUP
Abstract Copyright:
(c) 2015: Copyright © Cambridge University Press 2015
DOI:
10.1017/S002237781400124X
Bibliographic Code:
2015JPlPh..81c9006W

Abstract

To rigorously model fast ions in fusion plasmas, a non-Maxwellian equilibrium distribution must be used. In this work, the response of high-energy alpha particles to electrostatic turbulence has been analyzed for several different tokamak parameters. Our results are consistent with known scalings and experimental evidence that alpha particles are generally well confined: on the order of several seconds. It is also confirmed that the effect of alphas on the turbulence is negligible at realistically low concentrations, consistent with linear theory. It is demonstrated that the usual practice of using a high-temperature Maxwellian, while previously shown to give an adequate order-of-magnitude estimate of the diffusion coefficient, gives incorrect estimates for the radial alpha particle flux, and a method of correcting it in general is provided. Furthermore, we see that the timescales associated with collisions and transport compete at moderate energies, calling into question the assumption that alpha particles remain confined to a flux surface that is used in the derivation of the slowing-down distribution.
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