Description
Fast ions accelerated by ion-cyclotron resonance frequency (ICRF) waves tend to form highly anisotropic distribution functions. These distributions play an important role in the collisional redistribution of the absorbed power to the thermal background ions and electrons, stabilising or destabilising both MHD eigenmodes and plasma turbulence. Modelling the distribution functions, however, presents a computational challenge, typically requiring the solution of 2D or 3D kinetic equations.
This work advances two distinct modelling approaches to this problem. First, we have extended the LUKE code [1], which is widely used for modelling electron cyclotron resonance heating (ECRH) and lower hybrid current drive (LHCD) as well as runaway electrons. The code solves the linearized bounce-averaged relativistic Fokker-Planck equation for electrons. We have extended LUKE with an ion collision operator and the quasi-linear operator of Eriksson and Helander [2], enabling its application to ions. Second, we employ the recently developed Foppler code [3], which efficiently calculates a 2D distribution function by solving a 1D equation. Foppler combines a pitch-angle averaged Fokker-Planck equation with a model for the pitch angle distribution, presently based on the Dendy model [4].
We present the first results of ICRF-generated fast ion distributions from the extended LUKE code and compare them with calculations from Foppler, with both codes utilizing wave-fields from the full-wave solver FEMIC [5]. Furthermore, we show results obtained using different models for the pitch angle distribution, including the Dendy model [4] and the PION model [6].
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