Effect of constant collision mean free time on the boundary layer of the active collisional warm plasma

Mansour Khoram,S Farhad Masoudi

doi:10.1038/s41598-021-97750-1

Abstract

The plasma boundary layer is analyzed for a plasma in contact with a conducting plain surface where the ion temperature is comparable with the electron temperature and the plasma pressure is sufficiently high. The variations of electrical potential from the plasma-presheath boundary to the wall is studied using the fluidal formalism of plasma in three approaches; plasma and sheath asymptotic solutions and full solution. In the full solution approach, fluidal equations lead to a singularity when the ion velocity reaches the ion thermal speed. It is shown that removing the singularity causes a well-defined eigenvalue problem and leads to smooth solutions for the model equations. Some of the applicable aspects such as the floating velocity and density of ions, the floating electrical potential and an estimation of the floating thickness of the boundary layer are obtained. The dependency of these quantities on the ionization degree, the ion temperature and ion-neutral collision is examined too.

Highlights

Ions are created by electron impact ionization in the active plasma that allows the plasma boundary layer to be formed
Considering the effects of space-charge, the mathematical description of plasmas boundary layer by means of the hydrodynamic or √fluidal equ√ations leads to a singular point when the mean velocity of ions reaches the ion thermal speedUr = τ
By removing the singularity and finding smooth solutions, the essential smoothing conditions around the singular point within the boundary layer of plasma is investigated which leads to a well-defined eigenvalue problem

Summary

Introduction

The present paper investigates the boundary layer of thermal electropositive plasma from the presheath edge, with quasi-neutrality condition, to the floating wall, when the ions temperature is comparable to the electrons temperature and there is an elastic ion-neutral collision with constant ion mean free time. By receding from the floating wall, the normalized electrical potential is reduced and saturated to the constant potential φb at the plasma-sheath border which is an increasing function of the collision parameter in accordance with Eq (21-a).

Results

Conclusion