Post-streamer laser-perturbation of a positive corona discharge in ambient air

Abstract

A laser perturbation of a positive corona discharge is performed in ambient air. This latter is a self-sustained discharge composed of recurring current pulses resulting from propagation of an ionizing potential wave through a streamer process. The period T of the regime is about 100-120 mu s. The laser shot occurs between two successive recurring pulses at a given time tau , referred to the first recurring pulse, and at a given position X on the gap axis, referred to the plane. The laser is an excimer one (XeCl at 308 nm). The power density at the focal point is about 2.4*103 MW cm-2, so that no optical breakdown occurs. Nevertheless, we observe that the laser shot induces a streamer type pulse: depending on values of both tau and X, this streamer travels through the whole gap or only part of it, and the next recurring current pulses of the discharge occur later, their regime being undisturbed. Then, critical values tau c and Xc are defined. We observe that laser perturbation first propagates from X towards the rod, and then the cathode-directed streamer develops from the rod. Assuming that the laser shot creates primary electrons through a multiphoton effect, these photoelectrons drift from the X position towards the anode until their density is sufficient to allow propagation of the streamer.