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Highly Temporal Visualization of Generation Process of Underwater Secondary Streamer From Developed Primary Streamer

A series of images of a generation process of an underwater secondary streamer from a developed primary streamer was visualized by an ultrahigh-speed camera with a microscope lens. The secondary streamer with a filamentary structure propagated with an average velocity of 30 km/s from one of the channel tips of the semispherical primary streamer with an average propagation velocity of 1.8 km/s. The synchronized current waveform showed that pulsed currents of about 100 mA were changed into a continuous current of about 300 mA when the secondary streamer started to propagate. This experiment was carried out by the application of a single-shot pulsed positive voltage to a needle-to-wire electrode system with a gap length of 6 mm.