Dynamics of a self-sustained volume discharge in laser-shock-disturbed SF6-based mixtures

This paper reports on first systematic investigations into the dynamics of a self-sustained volume discharge (SSVD) in SF6-based mixtures pre-irradiated by a pulse CO2 laser. Two different illumination geometries are considered, one with a diaphragm slit arranged normal to the central electric field line of the discharge gap and the other with the discharge gap being wholly irradiated. The pattern of a laser-induced gas dynamic disturbance has been theoretically drawn starting from a shock wave theory and visualized by taking SSVD photographs. The delay times between the laser and voltage applications were varied from a few to several tens of microseconds. It has allowed us for the first time to obtain information, based on measuring the discharge voltage, about how long the mixtures considered are capable of being exposed to high temperature with no dissociation. The dynamic barrier effect found in our previous works is thoroughly investigated in both illumination geometries and the observed discharge patterns are qualitatively treated in terms of the electric field distortion by the surface charges at the shock wave fronts. The corresponding surface charge density is numerically estimated. The concept of controlling the electric field distribution over the discharge gap using the dynamic barrier effect is put forward.