Two-way, velocity-space resolved coupling between Fokker-Planck code CQL3D and the Monte-Carlo neutral particle code FIDASIM

In this contribution we present results on the two-way coupling between the continuum Fokker-Planck (FP) code CQL3D [1] and the Monte-Carlo (MC) neutral particle code FIDASIM [2]. CQL3D is a continuum bounce-averaged FP code with a fully non-linear collision operator. In this work, we aim to self-consistently calculate neutral beam attenuation, ion sources, ion sinks and halo neutral production using non-thermal ion and electron distribution functions calculated with CQL3D. This setup has been applied to tokamaks and also magnetic mirror plasmas.



Application to the tokamak includes an ITER case where FIDASIM is used to develop a simplified model for the cold neutral gas source from the 1^st wall. This cold gas penetrates the main plasma and becomes a source for Charge-Exchange (CX) with confined fast ions. When these fast neutrals aren’t lost to the 1^st wall, they penetrate the plasma and can experience multi-step CX events and effectively result in radial transport of fast ions. We discuss how this simplified model could be coupled to more sophisticated neutral gas codes which specify the characteristics of the 1^st wall neutral gas source.



Application to the mirror concept includes the Wisconsin High field Axisymmetric mirror (WHAM) to model neutral beam attenuation and fueling in a CX-dominated plasma using non-thermal distribution functions for both electrons and ions. We describe the calculation of the ion sink term which originates from the neutralization of fast ions and the associated replacement by warm ions (ion source) sampled from the halo and beam neutral population.



[1] R. W. Harvey, Nucl. Fusion 59 106046 (2019)

[2] B. Geiger et al., Plasma Phys. Control. Fusion, 62 105008 (2020)