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

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Abstract
The authors studied the extent to which Maxwellian and bi-Maxwellian series expansions can describe plasma flows characterised by non-Maxwellian velocity distributions. The problem they 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. They found that, in general, the bi-Maxwellian-based 16-moment expansion for the velocity distribution function is better suited to describing anisotropic plasmas than the Maxwellian-based 20-moment expansion. They also found that for large electric fields the distribution function displays toroidal and bean-shaped characteristics, depending on the collision-to-cyclotron frequency ratio.