A collisional model of the plasma presheath

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Abstract
The problem of a collisional plasma flowing into a perfectly absorbing wall has been investigated using a kinetic approach. The plasma is assumed to have a nonzero ion temperature and a Boltzmann distribution of electrons. Ion collisions are included in the analysis through a Bhatnagar–Gross–Krook (BGK) collision term. An equation describing the electrostatic potential variation in the presheath region is derived. This equation is solved numerically for a range of collisionalities. In addition to the potential variation in the presheath, the ion distribution function, the wall potential, and the ion particle and energy fluxes into the sheath are also calculated. The calculation is repeated for three different cases. In the first case ion–neutral collisions are modeled by conserving only particles in the BGK operator. Ion–ion collisions are modeled by conserving particles and momentum in the second case, and by conserving particles, momentum, and energy in the third case. These results give insight into the role of collision conservation laws in describing the plasma flow.

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