PPPS-2013: Analysis of secondary electron emission of dielectric materials using a direct kinetic simulation

Abstract

Secondary electron emission (SEE) plays an important role in the interaction of a plasma and dielectric materials which are used in electric propulsion devices. It has been proposed by Hobbs and Wesson that the near-wall sheath becomes space charge limited for an SEE coefficient larger than a critical value <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> . In their analysis, the SEE coefficient is assumed to be the ratio of currents of cold secondary and warm primary electrons, and the material dependence of the SEE coefficient is not taken into account. The purpose of this investigation is to understand the SEE effects on the collisionless sheath structure near a dielectric material. A direct kinetic simulation <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , in which the Vlasov equation is solved to directly obtain the velocity distributions of the plasma components, is used to model the collisionless sheath in the presence of SEE. The numerical results which assume cold secondary electrons are in good agreement with Hobbs and Wesson's exact and approximate solutions. We also investigate the sheath structure accounting for a velocity distribution of electrons that are reflected and emitted from the dielectric material. The SEE effects on the near-wall sheath of dielectric materials are discussed.