Kinetic analysis of the plasma boundary layer in an oblique magnetic field

A kinetic analysis is presented to study the influence of a strong oblique magnetic field on the plasma boundary layer in front of an absorbing wall. The ion transport is provided by (a) magnetic field lines intersecting the wall and (b) by charge exchange collisions with neutrals. The Debye length λD is small compared with the ion gyroradius ρi and the electrons are Boltzmann distributed. For the limiting case λD→0 and cold neutrals, an efficient method is developed to calculate the self-consistent stationary solution of the ion Boltzmann equation. The resulting ion distribution functions exhibit an involved structure. The kinetic Bohm-criterion is found to be fulfilled marginally. To investigate the stability of the solution, the analysis is supplemented by a particle simulation. It is shown that the involved structure of the stationary ion velocity distribution is smeared out (a) by an ion cyclotron instability (cold gas) and (b) by a finite gas temperature. The potential profiles and ion distributions resulting from the self-consistent kinetic analysis are compared with expectations based on a previous hydrodynamic model.