Moment models for neutral particles in high-collisional regimes for plasma edge simulations

Neutral particles play an important role in the plasma edge of a fusion machine, protecting the power exhaust against excessive heat loads due to the incoming plasma. The neutral particles in the plasma edge are described by a high-dimensional kinetic equation that captures their movement and interactions with the plasma. In the high-collisional limit of this kinetic equation, the classical solution procedure of using a Monte Carlo method becomes intractable. This paper investigates the use of so-called moment models, which already have proven their value in rarefied gas dynamics, as a low-dimensional and cheap substitute for the kinetic equation. Three hyperbolic moment models are derived: a linear one which incorporates information about the given plasma particle distribution in the ansatz, and two non-linear ones which incorporate information about the neutral particle distribution itself. The accuracy of these moment models is assessed in two numerical experiments.