Transient current and sheath motion following the photoelectron-initiated avalanche in dc glow discharges

Abstract

We have performed time-resolved observations of the current, optical emission, and electric field profiles in an Ar +2% K dc glow discharge, following the pulsed-laser-induced photoelectron emission on the cathode. These observations indicate that (1) The photoelectron-initiated avalanche results in a strong perturbation of the charge distribution in the discharge. This can be observed as a considerable shortening of the sheath length. (2) This leaves the discharge in a nonstationary regime, with a highly enhanced conductance. It then relaxes to the initial, steady-state regime in a time which is about 100 \ensuremath{\mu}s in our conditions. This time is both considerably larger than the ion transit time in the sheath and shorter than the ambipolar diffusion time. Self-consistent macroscopic simulations have been done and found to be in excellent qualitative agreement with the observations. Monte Carlo microscopic simulations of the ionization in the sheath have also been performed to point out some shortcomings of the ``beam model'' used in the self-consistent simulations.