Numerical Examination of the Effects of Ion Thermal Flow on Plasma Sheath Characteristics

The effects of ion thermal flow on the electric and hydrodynamic characteristics of a plasma sheath are examined using a multi-fluid model. In comparison with cold plasma, ion pressure is modeled by a power law dependence on the ion density in warm plasma. The pressure force on the ion depends on the ion density, ion temperature, and a nearly constant parameter called the ion polytropic coefficient. Two well-known quantities for this coefficient, γ_i =1 and 3, are considered, corresponding to isothermal and adiabatic flows, respectively. The numerical calculations show that increasing the ion temperature decreases the sheath thickness and increases the ion impact energy and ion saturation current at the wall. The ion polytropic coefficient has the same effect as the ion temperature and intensifies the ion temperature effects.