Fully implicit coupling of fluid plasma and kinetic neutral models using differentiable Monte-Carlo methods

The use of coupled continuum and kinetic simulations is ubiquitous in modeling various tokamak operation scenarios. Most often, continuum models employ finite-volume or similar methods, while kinetic simulations rely on Monte-Carlo methods. The statistical nature of Monte-Carlo codes, however, generally forces the use of explicit coupling methods, which can suffer from classic numerical instabilities and require huge computational resources. It has been suspected for some time that correlated Monte-Carlo methods should allow the use of fully implicit coupling methods, which enjoy much more robust stability properties and allow large time-steps to resolve long-timescale phenomena with minimal runtimes. I will show results realizing a fully-implicit coupling scheme in one spatial dimension relying on a homemade ``differentiable'' correlated Monte-Carlo code coupled to the UEDGE plasma code, and discuss progress towards the two-dimensional case. This poster is based on joint work with Maxim Umansky and Ben Dudson.