Optical diagnostics of shock waves generated by a pulsed streamer discharge in water

The use of a pulsed streamer discharge in water to kill algae has led to investigations to determine the degree of influence of potentially lethal byproducts of a streamer discharge. The primary byproducts that may influence the lethality of a streamer discharge on algae cells include the localized electric field, shock wave production, OH and O/sub 3/ radical production, and ultraviolet light production. In the studies reported here, the shock waves generated by a pulsed streamer in distilled and tap water are optically imaged to characterize their temporal history. The streamer discharge was produced in a thin sheet of water using a stainless steel needle and wire geometry with a 2 cm gap between electrodes. This allowed a two dimensional view of the generated shock waves propagating away from the streamer discharge region. A 600 ns pulse with amplitudes of up to 60 kV was applied to the electrodes utilizing a 360 /spl Omega/ Blumlein generator and transformer. A laser schlieren imaging setup combined with a high speed CCD camera with 1.5 ns gating capability captured the temporal history of the shock waves over a series of reproducible discharges. Streamer discharges were observed producing a series of shock waves as they propagated from the needle tip. These shock waves would combine by interference producing a distinct shock wave pattern propagating radially outward at 1.45 km/sec. A second shock wave generating event is observed up to 150 /spl mu/sec after the streamer discharge dissipates. Generation of a single uniform shock wave was also observed at voltage levels associated with the minimum amplitude required for streamer production.