Analysis of ion orbits in front of a negative planar electrode immersed in an oblique magnetic field

Abstract

The orbital motion approach is used to analyze the ion impact on a negatively biased planar wall immersed in a strongly magnetized plasma. It is assumed that the given homogeneous magnetic field forms a small angle with a planar negatively biased electrode, while the inhomogeneous electric field is perpendicular to the electrode. Spatial dependence of the electric field is modeled in such a way that the electric field exhibits two-scale behavior, which is characteristic of plasma sheath problems. The equation of motion of a singly charged deuterium ion is solved for a large variety of parameters and initial conditions. The effects of electrode bias, magnetic flux density, magnetic field angle, initial velocity, electric field scaling, and electrode bias are investigated. It is found that the impact angles of ions are distributed over a surprisingly wide range, and in a vast majority of cases, the angle of impact is several times larger than the magnetic field angle. The study is relevant for the analysis of ion flow to the electrodes in fusion plasmas, i.e., divertors of tokamaks.

Two-dimensional collisional particle model of the divertor sheath with electron emissive walls

“…More recently, Khaziev and Curreli [6] have studied the plasma-wall transition at arbitrary angles between the magnetic field and the material surface with both a 1D fluid model and a 1D PIC code, showing that a correct quantitative prediction of the ion energy and impact angle distributions at the wall requires a kinetic treatment. Such distributions are particularly relevant for the induced wall sputtering and can deviate significantly from the optical (impact along the magnetic field direction) or fluid (impact along the average ion velocity) approximations, even in collisionless scenarios, as also predicted by ion orbit studies [7]. A recent work by Thompson et al [8] includes the effects of ion/neutral collisions in a similar 1D PIC code.…”