Effects of a monoenergetic electron beam on the sheath formation in a plasma with a q-nonextensive electron velocity distribution

Abstract

The characteristics of a plasma sheath consisting of nonextensive electrons and thermal ions in the presence of a monoenergetic electron beam is studied in the framework of a one dimensional hydrodynamic model. Because of the electron beam, bulk electron distribution of plasma is assumed to be non-Maxwellian in general. Using the Sagdeev pseudopotential method, a modified Bohm criterion is obtained. It is shown that the criterion is significantly affected by the nonextensivity degree (q) and the beam parameters. The criterion is reduced to the standard form of the Bohm criterion when (i) the electrons have Maxwellian distribution (q→1), and (ii) the beam density is taken to be zero. A small amplitude analytical solution is also given for the potential in the sheath region. Moreover, assuming the total current on the electrode surface to be negligible, the floating potential is derived. The set of nonlinear hydrodynamic equations is solved numerically and the effects of many parameters such as nonextensivity, beam density, and velocity on the electric potential of the sheath region, ion density, and sheath thickness are studied. It is shown that the electron beam can control the potential and ion density of the sheath region.