Oscillations of the collisionless sheath at grazing incidence of the magnetic field

Abstract

An Eulerian Vlasov code is used to study the physics of a collisionless sheath with grazing angles of incidence of the magnetic field. The electrons are treated with a parallel-B kinetic equation. In the case where the ion gyroradius is large compared to the Debye length, the electrons, frozen by the magnetic field line, have to move rapidly along the magnetic field B in their attempt to follow the ions gyrating perpendicular to B. Below a critical angle of incidence of the magnetic field, the large gyroradius ions can be scraped off at the plasma-wall interface of the sheath. The electrons now determine the characteristic time for information propagation, with low frequency oscillations appearing in the system. In the case where the ion gyroradius is reduced to the same order as the Debye length, the results evolve closer to those of the classical sheath, and the amplitude of the low frequency oscillations is reduced.