  In some inertial confinement fusion hohlraum designs, the inside plasma is
not sufficiently collisional to be satisfactorily described by the Euler
equations implemented in hydrodynamic simulation codes, particularly in
converging regions of the expanding plasma flow. To better treat that
situation, this paper presents an extended hydrodynamics model including higher
moments of the particle velocity distribution function, together with
physically justified closure assumptions and relaxation terms. A preliminary
one-dimensional numerical implementation of the model is shown to give
satisfactory results in a test case involving a high-velocity collision of two
plasma flows. Paths to extend that model to three dimensions as needed for an
actual hohlraum geometry are briefly discussed.
