Abstract Details

Add files

Efficient calculation of impurity transport and an improved slowing-down distribution for alpha particles

Author: George J. Wilkie
Requested Type: Consider for Invited
Submitted: 2015-01-19 19:53:12

Co-authors: M. Landreman, I. G. Abel, W. Dorland

Contact Info:
University of Maryland
IREAP, AV Williams Bldg, Paint
College Park, MD   20742
United States

Abstract Text:
Fusion devices can contain a number of high-energy, weakly-collisional species that are non-Maxwellian and are used to heat the plasma and/or drive plasma current. Where and how these particles deposit their energy and momentum is determined by their flux in phase space due to microturbulence, coherent modes, and collisions. Previous work [1], using alpha particles as a prototype of fast ions, demonstrated that the equilibrium energy distribution can have an important effect on the turbulent flux. Furthermore, the resultant transport can compete with collisionality, altering the distribution from the pure slowing-down form. In principle, one can calculate the fully-turbulent flux of a passive species with any non-Maxwellian distribution with any gradient using the results of only one local simulation. We present such a method that takes advantage of the linearity of the gyrokinetic equation in the trace-species limit. As a proof-of-principle, we apply this technique to estimating the flux of alpha particles using several different models of the velocity-space distribution. These models improve on the analytic slowing-down distribution by including: the transition to Maxwellian at low energy, a realistic source of alpha particles, and energy-dependent radial transport effects. The impact of these effects on destabilized Alfven modes are also analyzed.

[1] G. Wilkie, I. Abel, E. Highcock, W. Dorland. "Validating modelling assumptions of alpha particles in electrostatic turbulence." To appear, Journal of Plasma Physics. arXiv:1408.4967

Comments: