  In many applications, such as 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 comparison of the variance and computational cost of a coherent set
of such estimation procedures. We compare the different estimation procedures
for mass in a simplified forward-backward scattering model problem, where an
analytical comparison is possible, and for mass and momentum in a model problem
with realistic scattering. Our results reveal a non-trivial dependence of the
optimal choice of estimator on the model parameters and show that different
estimation procedures prevail for different quantities of interest.
