Particle trajectories in a sheath in a strongly tilted magnetic field

In this paper we provide a systematic analysis of particle motion in a sheath under the condition that the magnetic field intersects the wall at a small angle. A general qualitative classification of particle trajectories is presented. It is shown that the ion motion in the ion subsheath can be described in terms of an adiabatic invariant, despite the fact that the electrostatic potential varies on a scale comparable with the ion gyroradius. Trajectories of heavy impurity ions for the cases of both low and high ionization states have been found. Electron motion is considered, and it is shown that, if the electron gyroradius is much less than the electron Debye radius, electrons hit the wall at shallow angles. The possible role of an electrostatic field directed along the wall is briefly discussed. The results obtained in the paper can be used for evaluating the sputtering rate and the secondary emission coefficient, as well as for analyzing sheath stability and for formulating the boundary conditions for the bulk of the plasma. (C) 1998 American Institute of Physics.