Breakdown Initiation in Water with the Aid of Bubbles

The breakdown initiation in water is investigated using artificially produced long-lived microbubbles $40$–$100$ $\mu$m in size obtained with the aid of a pulse-heated wire electrode. In all cases, the discharge is initiated in a bubble, with the prebreakdown time in the presence of a bubble being much shorter than in its absence. In the case of a discharge from the anode, three series of shock waves are observed in the electrode region, associated with the ignition of the discharge, the propagation of a supersonic streamer, and the release of energy when the streamer closes the interelectrode gap. In the case of cathode breakdown initiation, disturbances develop on the bubble surface in the form of a "bush" propagating at a subsonic speed in the direction of the opposite electrode. The possibilities of streamer and multiavalanche mechanisms of the breakdown of microbubbles are discussed.