Kinetic Modeling of Neutral Beam and Edge Neutrals in Plasma Confinement Devices Using FIDASIM and CQL3D-M

We present recent developments in the FIDASIM Monte-Carlo code and the bounce-averaged Fokker-Planck code CQL3D-M for modeling beam and edge neutral fueling with realistic vacuum vessel geometries. By recasting FIDASIM as an iterative solver to the Linear Boltzmann Transport Equation (LBTE), we enable self-consistent computation of the steady-state atomic hydrogen neutral gas distribution across the entire plasma–vessel volume consistent with wall boundary conditions and the plasma state from CQL3D-M.



A two-way coupling scheme enables the time-dependent evolution of the kinetic neutral and plasma distributions, allowing for realistic modeling of experimental conditions. We apply this framework to the WHAM mirror device, analyzing the effects of vacuum vessel geometry, pumping scenarios, and getter surfaces on the neutral-plasma interaction. When charge exchange reactions dominate, modeling beam transport using an LBTE approach produces a non-negligible enhancement in the neutral beam assimilation. We also present results using non-thermal ion distributions for beam stopping and outline future extensions to incorporate more realistic wall interaction models and molecular hydrogen physics.



This work was supported by Realta Fusion, the DOE Milestones program award number DE-SC0024887 and RF SciDAC Partnership DE-SC0024369