Influence of the inaccuracy of the plasma potential on the shape of the electron distribution function obtained from the probe characteristic

摘要

Peculiarities of the recovery of the electron distribution function (EDF) from the voltage–current characteristic (VCC) of a probe by solving an integral equation for the probe in the kinetic regime (electron energy relaxation length much larger than the dimensions of the probe and of the region disturbed by the probe) are considered. When the gas pressure is not smaller than several Torr, the inaccuracy of the plasma potential results not only in a shift of the EDF along the energy axis (as at low pressures when the probe is in the collision-less regime) but also in the considerable deformation of the EDF recovered from the VCC. In this paper, a detailed analysis of this effect is carried out. The character of the deformation is demonstrated in the results of the model calculations at different plasma potential shifts, at different pressures, for monotonic EDFs and for EDFs with maxima. The integral equation (ill-posed problem) is solved by the Tikhonov regularization method. Probe measurements of the EDF are performed in a stratified discharge when the plasma potential oscillates and its error is larger than in the case of the homogeneous discharge. The influence of the inaccuracy of the plasma potential on the shape of the EDF obtained in experiment is investigated.