Two-fluid simulation of expansion and confinement of pellet-produced hydrogen clouds in hot magnetized plasmas

The structure of dense particle clouds surrounding ablating hydrogen isotope pellets is investigated with primary attention to the B-perpendicular expansion and deceleration dynamics. In order to distinguish between the cross-field (radial) motion of charged particles and that of neutrals, the model is based on a two-fluid approximation. A 1.5-D Lagrangian numerical method is used for solving the system of MHD equations. The characteristic cloud radius and radial distributions of temperature, particle densities, and other flow properties are calculated by means of this two-fluid - single-temperature model. The results show that collisional coupling between the neutral and ionized components is strong enough to change the initially spherically symmetric expansion of the neutral particles to a field-aligned flow pattern, in agreement with the experimentally observed elongated radiation emission patterns of the excited neutral atoms. Calculated clouds parameters are compared with measured data and with results stemming from comparative calculations. (orig.)