Validating modelling assumptions of alpha particles in electrostatic turbulence

摘要

To rigorously model fast ions in fusion plasmas, a non-Maxwellian equilibriumdistribution must be used. In the work, the response of high-energy alphaparticles to electrostatic turbulence has been analyzed for several differenttokamak parameters. Our results are consistent with known scalings andexperimental evidence that alpha particles are generally well-confined: on theorder of several seconds. It is also confirmed that the effect of alphas on theturbulence is negligible at realistically low concentrations, consistent withlinear theory. It is demonstrated that the usual practice of using ahigh-temperature Maxwellian gives incorrect estimates for the radial alphaparticle flux, and a method of correcting it is provided. Furthermore, we seethat the timescales associated with collisions and transport compete atmoderate energies, calling into question the assumption that alpha particlesremain confined to a flux surface that is used in the derivation of theslowing-down distribution.