Free path and scattering probability of ions in a glow discharge sheath

The transport of ions in a dc glow discharge sheath is modeled taking into account the ion energy dependence of ion-molecule collision cross section. The free path and the scattering probability of ions are obtained as a function of two parameters: the ratio of sheath thickness to ion mean free path, d is/l0, and the ion energy dependence of the collision cross section. The effect of ion energy on free path and scattering probability has been calculated for Ar discharge and found to be significant in typical discharge conditions. The probability of multiple scattering of ions in the sheath is formulated and calculated in 3 dimensions. The result shows that the probability of multiple scattering decreases with decreasing d is/l0 and increasing ion energy.