A comparison of source term estimators in coupled finite-volume/Monte-Carlo methods for plasma edge simulations innuclear fusion

In plasma edge simulation of a nuclear fusion reactor, a coupled PDE/kinetic description is required, which is usually solved with a coupled finite-volume/Monte-Carlo method. Different procedures have been proposed to estimate the source terms in the finite volume part that appear from the Monte Carlo part of the simulation. In this paper, we present a systematic (analytical and numerical) comparison of the variance and computational cost of a coherent set of such estimation procedures. We perform a study of the expected statistical error and computational cost of these estimation procedures as a function of the model parameters, revealing a non- trivial dependence of the optimal choice of estimator on these parameters. We consider a simulation with realistic scattering and also show the dependence of the optimal estimator on the problem parameters in this case. We furthermore extend our analysis from mass source estimation to momentum source estimation, showing different estimation procedures prevail for both quantities of interest.