Coupling between the Fokker-Planck code CQL3D and the Monte-Carlo neutral particle code pyFIDASIM

As part of the RF-SciDAC effort, in this contribution we describe recent progress towards the goal of two-way (velocity-space resolved) coupling between the continuum Fokker-Planck (FP) code CQL3D [1] and the Monte-Carlo (MC) neutral particle code pyFIDASIM. CQL3D is a continuum bounce-averaged FP code with a fully non-linear collision operator. CQL3D is typically used in tokamaks to calculate the ion/electron distribution functions in presence of RF heating and neutral beam (NB) injection. pyFIDASIM, the Python implementation of FIDASIM [2], is a 3D MC code used for NB deposition modelling which tracks neutrals/excited states as they cross the plasma and provides means for resolving fast ion (FI) birth points and halo neutral dynamics.



This coupling effort has been motivated by the need to include velocity-space charge-exchange (CX) sources and sinks in FP calculations where non-thermal effects on both ions and neutrals are expected to be significant such as in HHFW heating of beam-produced FIs in tokamaks and CX-dominated NB deposition in mirror devices. In this contribution, we describe the use of pyFIDASIM to provide FI birth points for the CQL3D FP calculation. Results are compared with those provided by CQL3D’s own NBI deposition model NFREYA. Finally, we discuss the impact of the results, propose strategies to implement velocity-space resolved source/sink data exchanges and outline next steps for the project.



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

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