A fluid treatment of the plasma presheath for collisionless and collisional plasmas

Abstract

The presheath region of an unmagnetized plasma is treated using ion fluid equations in the collisional and collisionless regimes. Effects of neutral gas–plasma interactions are included through source terms in the fluid equations. Ion–ion collisional effects are included through the closure conditions of the fluid equations. In the collisionless regime, the perpendicular ion temperature is assumed constant and independent of the parallel ion temperature. In the collisional limit, the parallel and perpendicular temperatures are assumed equal throughout the presheath. Profiles of ion density, flow velocity, parallel temperature, and energy flux obtained by integrating the fluid equations compare well to previously published kinetic results in the collisionless case. Ion–ion Coulomb collisions are shown to have a negligible effect on the ion particle and energy flux into the sheath.