Development of a spark sustained by charging the stray capacitance of the external circuit in atmospheric-pressure nitrogen

Results are presented from experimental studies and numerical simulations of a spark discharge excited in a short point-plane gap filled with atmospheric-pressure nitrogen. The discharge was powered from a high-voltage source connected to the discharge gap through a large ballast resistance. In this case, a short-term spark develops only due to the charging of the stray capacitance of the external circuit; therefore, the energy released by the spark and its intensity are both low. Rapid current growth in a weak spark is accompanied by the contraction of the current channel rather than by its gasdynamic expansion, as it occurs in long-duration kiloampere sparks. Simulations show that, because of the very short spark lifetime, the plasma in a weak spark is substantially nonequilibrium and the gas temperature is fairly high.