Assessment of a fractal model for corona discharges in salt water

The prebreakdown corona phase of a spark discharge in salt water produces a measurable acoustic pulse. This pulse is produced by the formation and collapse of a vapor bubble. The plasma has a multiply fingered shape, and it creates a bubble with a corresponding acoustic pulse. The rate of formation of plasma fingers may be a fractal dimension of the size of the discharge. A fractal model of the growth of the corona discharge can be used to connect the variables of voltage, current, and bubble wall acceleration. The dependence of the acoustic and electrical response and thus the fractal dimension of the corona growth on liquid conductivity, and applied voltage are investigated. The acoustic data are used to infer the bubble wall acceleration while the current-voltage data are measured directly and used to determine the total resistance of the plasma. The corona is formed by the application of high-amplitude electric fields to a set of electrodes that are immersed in the liquid. [Work supported by the Office of Naval Research under Grant No. N00014-94-1-0150.]