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Validating modeling assumptions of alpha particles in electrostatic turbulence

Part of: Focus on Fusion

Published online by Cambridge University Press:  21 January 2015

G. J. Wilkie ,
I. G. Abel ,
E. G. Highcock  and
W. Dorland
G. J. Wilkie*
Affiliation:
University of Maryland, College Park, MD 20742, USA
I. G. Abel
Affiliation:
Princeton University, Princeton, NJ 08544, USA
E. G. Highcock
Affiliation:
University of Oxford, Oxford OX1 3NP, UK
W. Dorland
Affiliation:
University of Maryland, College Park, MD 20742, USA
*
†Email address for correspondence: [email protected]
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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.

Type
Research Article
Information
Journal of Plasma Physics , Volume 81 , Issue 3 , June 2015 , 905810306
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Copyright
Copyright © Cambridge University Press 2015 

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