Plasmas in quasi-static external electric fields

摘要

This work develops some practical approximations needed to simulate a high plasma density volume bounded by walls made of dielectrics or metals which may be either biased or floating in potential. Solving Poisson's equation in both the high-density bulk and the sheath region poses a difficult computational problem due to the large electron plasma frequency. A common approximation is to assume the electric field is computed in the ambipolar approximation in the bulk and to couple this to a sheath model at the boundaries. Unfortunately, this treatment is not appropriate when some surfaces are biased with respect to others and a net current is present within the plasma. This report develops some ideas on the application of quasi-static external electric fields to plasmas and the self-consistent treatment of boundary conditions at the surfaces. These constitute a generalization of Ohm's law for a plasma body that entails solving for the internal fields within the plasma and the potential drop and currents through the sheaths surrounding the plasma.