Experimental evidence of bubble model of discharge initiation

Bubble model of pulse discharge initiation is based on the next suppositions. Bubbles of micron sizes exists on electrodes or can emerges during pulse duration. Electrical stress can lead to gas discharges in bubbles. After discharge in bubble its´ surface is supplied by charge carriers. Coulomb force leads to bubble deformation. Field increase near bubble poles up to some level E_m can be sufficient for discharge propagation in liquid. The computation of this model performs to explanation of a lot of breakdown dependencies such as volt-time characteristics, pressure dependencies, temperature dependence, area effect and so on. Nevertheless there is no the experimental basement of the model. It is due to the experimental troubles that consist of very small bubble sizes and very short pulses. The analyze of own experimental data and the data of our colleagues was performed with the purpose to find the evidence of the bubble role. One managed to find optical data concerning the initiation of discharge by bubble on electrode in hexane and in nitrobenzene. In last case was used electrooptical Kerr effect that give the possibility to visualize the electric field after partial discharges and during discharge tree propagation. Several pictures shows the space charge and its´ motion away from electrode with electrohydrodynamical mobility