Presheath in Fully Ionized Collisional Plasma in a Magnetic Field

Abstract

The quasineutral presheath layer at the boundary of fully ionized, collisional, and magnetized plasma with an ambipolar flow to an adjacent absorbing wall was analyzed using a two fluid magneto-hydrodynamic model. The plasma is magnetized by a uniform magnetic field B, imposed parallel to the wall. The analysis did not assume that the dependence of the particle density on the electric potential in the presheath is according to the Boltzmann equilibrium, and the dependence of the mean collision time τ on the varying plasma density within the presheath was not neglected. Based on the model equations, algebraic expressions were derived for the dependence of the plasma density, electron and ion velocities, and the electrostatic potential on the position within the presheath. The solutions of the model equations depended on two parameters: Hall parameter (β), and the ratio (γ), where γ = ZTe/(ZTe + Ti), and Te, Ti and Z are the electron and ion temperatures and ionicity, respectively. The characteristic scale of the presheath extension is several times ri/β, where ri is the ion radius at the ion sound velocity. The electric potential could have a non monotonic distribution in the presheath. The ions are accelerated to the Bohm velocity (sound velocity) in the presheath mainly near the presheath-sheath boundary, in a layer of thickness ∼ ri/β. The electric field accelerates the ions in the whole presheath if their velocity in the wall direction exceeds their thermal velocity.

Fluid model of the sheath in front of a floating electrode immersed in a magnetized plasma with oblique magnetic field: Some comments on ion source terms and ion temperature effects

“…The sheath in a magnetized plasma in the presence of negative ions has been studied, [31][32][33][34][35] and even a combination of the presence of two positive and one negative ion species has been taken into account. 36,37 In the majority of the above mentioned papers, fluid models are used, although more sophisticated approaches like two fluid models 38,39 or particle-in-cell computer simulations [40][41][42][43] have also been used. Fluid models are based on the continuity equation and momentum exchange equation for ions-Eqs.…”

Plasma–wall transition in the quasi‐neutral region of collisional and stationary plasmas in a magnetic field enclosed by totally absorbing walls

“…Others can be added easily by following the calculations in this paper straightforwardly. The dependence of the ion-electron collision frequency ie on the ion density n i at a given constant temperature is considered in the following expression [10] with the constant̂i e : ie n i ≔̂i e = const.…”

“…In the case of ≲ e0 ∕Ω e , it additionally depends on the ratio of the convective and the diffusive electron flow. Alterkop et al [10] considered a quasi-neutral two-fluid model of ions and electrons with collisions between both species in a magnetic field parallel to the wall, in which the dependence of the collision frequency on the plasma density was taken into account and the electrons were not assumed to be in Boltzmann equilibrium. They stated that ions are accelerated toward the wall in a layer of thickness ∼ r i ∕ , where r i is the ion Larmor radius and = eB∕(m e ie ) the Hall parameter, both referring to the wall.…”

“…In this paper, basic investigations are carried out in a two-fluid model based on the model of Alterkop et al, [10] which is supplemented here by ionization and arbitrary external magnetic fields. The magnetic field is assumed to be so strong that the magnetic field induced by the charged particles is neglected.…”

Analysis of multi-dimensional techniques for particle modelling in tokamak edge plasma

“…review [1]. Especially there exists a considerable scientific and technological interest in processes taking part during the movement of charged particles in external magnetic fields [2]- [5] in both low-temperature and high-temperature plasmas. As the detailed analysis of experimental data obtained in such plasmas is rather difficult, the computational methods started to be very important.…”