Comparison of Maxwellian and bi-Maxwellian expansions with Monte Carlo simulations for anisotropic plasmas

The extent to which Maxwellian and bi-Maxwellian series expansions can describe plasma flows characterised by non-Maxwellian velocity distributions has been studied. The problem considered was the steady-state flow of a weakly ionised plasma subjected to homogeneous electric and magnetic fields, and both polarisation and hard-sphere collision models were used. Monte Carlo simulations provided a basis for determining the adequacy of a given series expansion. It was found that, in general, the biMaxwellian-based 16-moment expansion for the velocity distribution function is better suited to describing anisotropic plasmas than the Maxwellian-based 20-moment expansion. It was also found that for large electric fields the distribution function displays toroidal and bean-shaped characteristics, depending on the collision-to-cyclotron frequency ratio. (author)