Influence of Scattering and Ionization on RF Impedance in Glow Discharge Sheaths

The effects of scattering and ionization on the rf impedance of a glow discharge sheath are calculated using an equivalent dc sheath model. The effects of scattering are treated in terms of a drag force; equilibrium between the ion drift velocity and field is not required. The ratio of first ionization coefficient to pressure, α/p, is assumed to be constant, and the ion energy and ion current injected from the glow are assumed as initial parameters. In the limit of low pressures, the calculation agrees with the Child-Langmuir law. At intermediate pressures, the results agree with the mobility limited solution. At high pressures, the product of pressure and sheath dimension, pd, becomes constant because of ionization effects. The results of this calculation, obtained by numeric integration, can be accurately approximated by an interpolation formula. This formula provides a simple means for calculating the rf impedance of a sheath.