ИСТИНА

Formation of voids (micro-pores) in a vicinity of a pin electrode in a highly non-uniform electric field applied within a few nanoseconds was proposed recently as a main mechanism of electrical breakdown of liquid dielectrics1. We solve the problem of fluid dynamics when voltage pulse duration of 7 ns with a peak value of 300 kV was applied to a spherical electrode - plane setup. Motion of liquid (water) is described by the system of equations of hydrodynamics written in general terms in the spherical coordinates and the Tait equation of state. Electrostrictive force is taken in a form proposed for polar dielectrics2. Action of electrostrictive forces results in the formation of a shock wave, which propagates from the spherical electrode. The speed of the shock front reaches 3 Mach numbers. The rarefaction region is formed before the shock front, duration and peak value of which increases in a few nanoseconds. At some point, the negative pressure reaches a value at which liquid is ruptured and microcavity can be formed. The size of the cavities is determined by the rate a shock front growth. It is demonstrated that the size of cavities is sufficient to accelerate electrons to the energies of ionization of molecules of water vapor in the cavity.