Sheath Formation Criterion and Ion Flux for Non-Maxwellian Plasma

The criterion for the formation of a stable positive ion sheath is calculated for an arbitrary electron velocity distribution function to obtain the ion flux. The cases of Maxwellian and Druyvesteyn distributions are discussed for comparison. A diagnostic method for the positive ion density from the measured kinetic energy distribution by using the positive ion current region in the probe characteristic is suggested. The ion current density extractable from an ion source can also be estimated. Examples based upon experimental data are given to study the effect of non-Maxwellian velocity distribution.