Theory of an Electrostatic Probe in a Strong Magnetic Field. II

Abstract

A probe is considered in a magnetic field so strong as to impair collective transverse drifts. Then the charges supplied to the probe come mainly from a long tube of force, whose radius is about one Larmor radius larger than the probe. Assume that there is acting a diffusion process, more efficient than ordinary drifts, which continuously exchanges particles between the inside of the tube of force and the rest of the plasma. In a previous paper we have proposed a one‐dimensional model of this process, leading to an integro‐differential Poisson's equation, which has now been fully investigated in the case of slow diffusion. The solution consists of a chargeless, slowly decaying potential which describes the geometrical screening effect of the probe; while in the sheath an approximate boundary‐layer solution matches with the probe's potential V_P. The asymptotic relation between the current collected and V_P is computed. This model may be suited to the case of diffusion due to random wave fields.