Experimental Study of the Electric Pulse-Width Effect on the Acoustic Pulse of a Plasma Sparker

All types of seismic sources have a common feature in which large energy is released into water in a short time to produce an intense acoustic pulse. For plasma sparker, the discharge time is mainly determined by the discharge circuit parameters. Providing an accurate prediction of the acoustic pulse is difficult because of the complex plasma discharge process and unclear initial bubble condition. This paper presents the first experimental study on the influence of electric pulse width on acoustic pulses, especially the expansion pulse. Three comparative experiments are conducted to investigate the effect of electric pulse and to determine the minimum acoustic pulse width produced by a plasma sparker. One of the main results is that only the amplitude of the expansion pulse can obviously be changed if the electric circuit parameters are fixed, especially the capacitance of the energy storage capacitor. Meanwhile, the smaller the energy storage capacitor is, the shorter is the electric pulse and the narrower is the expansion pulse. The maximum pressure of an expansion pulse generated by a small capacitor is larger than that generated by a large capacitor under the same energy. The expansion pulse width decreases quickly when the energy dissipation on the load speeds up, and approaches the minimum value around several microseconds when the energy dissipation rate on the load is over 2 J/ μs, and the corresponding electric pulse width is on the order of hundreds of nanoseconds.