Formation of the radio frequency sheath of plasma with Cairns–Tsallis electron velocity distribution

Abstract

The effect of the non-Maxwellian plasma with enhanced electron tails on the properties of the radio frequency (RF) sheath is studied with a one-dimensional collisionless model, which consists of the sheath model and the equivalent circuit model. In the sheath model, electrons are assumed to obey the Cairns–Tsallis distribution. For various entropic indices q characterizing the degree of electron nonextensivity and parameter α measuring the electron nonthermality state, the electron nonextensivity and nonthermality are found to modify the potential drop across the sheath and the sheath thickness, as well as the spatiotemporal variations of the potential, the ion and electron densities inside the sheath. With the decrease in q and the increase in α, the potential drop across the sheath and the thickness increase at any time in a RF cycle as a result of the increase in superthermal electrons in the non-Maxwellian tail. The dependence of the potential drop across the sheath on q and α is deeply related to the frequency and amplitude of the disturbance current. When the electron nonextensivity and nonthermality are strengthened, the enhancement of the sheath potential drop can cause a significant increase in the ion bombardment energy on the wall, sheath power dissipation, and plasma energy flux to the wall.