Plasma-wall transition in two ion species plasma with bi-Maxwellian electrons

Abstract

Presheath and sheath structures of collisional two ion species (helium and argon) plasma in the presence of bi-Maxwellian electrons have been investigated by using a fluid model. As the thermal energy of hot electrons is higher than cold electrons, the electron impact ionization process is governed by the concentration of hot electrons. The velocity of positive ions at the sheath boundary, i.e., the Bohm criterion, gets modified in the presence of ion-neutral drag force, source term, and bi-Maxwellian electrons. It is found that the ion-neutral drag force, ionization rates, and volumetric composition of electrons affect the characteristics of the presheath and sheath. The scale length of the sheath region widens from about 1.09 mm to 5.80 mm with the increase in the concentration of hot electrons. The acoustic speed of helium ions at the sheath boundary is higher than its common speed, whereas the acoustic speed of argon ions is lower than its common speed. The common speed of positive ions at the sheath boundary is slower by 13% in magnitude than in the collisionless case. Furthermore, the effect of ion-neutral drag force on streaming instability for two ion species plasma has been systematically presented.