Release conditions of dust particle from plasma-facing wall in oblique magnetic field

Abstract

Release conditions of a spherical dust particle from a plasma-facing vertical wall immersed in an oblique magnetic field are studied analytically. The Poisson′s equation is solved in the magnetic pre-sheath and electrostatic Debye sheath to obtain the electric field at the wall, which repels the dust particle from the wall. The electric field decreases as the direction of the magnetic field approaches parallel to the wall. On the other hand the ion flow velocity becomes larger at moderate oblique angle than that without magnetic field. It is clarified that in the case of the strong magnetic field or the low plasma density the critical dust radius for the release of the dust increases as magnetic field becomes more acute. In the case of the weak magnetic field or the high plasma density, the critical radius disappears at the moderate angles of the oblique magnetic field. The surface roughness widely changes the angle between the magnetic field lines and the surface normal.