Structure of the plasma-wall interaction in an oblique magnetic field

Abstract

The influence of the magnetic field strength B and angle of incidence ψ on the one-dimensional (1-D) structure of a weakly collisional plasma near a charged wall is investigated. The models of Chodura [Phys. Fluids 25, 1628 (1982)] and Riemann [Phys. Plasmas 1, 552 (1994)] are recovered as particular cases: intermediate-B and weak-B cases, respectively, of the model presented here, and are compared with a third, strong-B case, where the space-charge sheath is partially magnetized. A triple structure comprising (collisional) presheath, Chodura layer, and sheath, exists only for the intermediate-B case. For weaker and stronger ranges of B, the Chodura layer disappears immersed into the presheath and the sheath, respectively, recovering a classical double-structure. In the Chodura model the importance of the collisional presheath to characterize completely the perturbation region is discussed. For the weak-B case: results for the whole range of angles of incidence are presented and compared; for grazing incidence and a near-collisionless plasma, an approximate analytical solution is derived; and, the asymptotic convergence to the triple-structure is shown. For the strong-B case, the analysis includes: (i) an involved derivation of the local behavior around the entrance point to the sheath, and (ii), for a certain range of ψ, to cross, with a regular solution, an internal singular point of the sheath equations. The similarities between the entrance conditions to the different plasma regions are pointed out.