Investigation of Three-Dimensional Characteristics of Underwater Streamer Discharges

We have developed a new three-dimensional (3D) observation method suitable for studying the structure of streamer discharges. Using this method we investigated the propagation of underwater streamer discharges generated in a nozzle-plate electrode system. As a result, the streamer branching angle was found to take a bell-shaped distribution having a mean value in the range of 65--75° with a standard deviation of about 20°. Moreover, we confirmed that the mean branching angle is a physical quantity that increases with water conductivity. The propagation velocity of the underwater streamer was estimated to be $(2{\mbox{--}}3) \times 10^{4}$ m/s.