Fast Breakdown Phenomena in Condensed Dielectrics under Pulsed Voltage Conditions

We proposed the model of anode-initiated electrical breakdown in water based on the concept of cascade Auger transitions of electrons in the valence band of the dielectric. We consider this model considering the conservation of short-range order in dielectric. The model explains how the process of the generation of free carriers in a strong electric field may result in the high velocities of propagation of the breakdown channels initiated from the anode. The estimation of change in conductivity of the breakdown channel is made using the data obtained in experiments carried out under high voltage (∼105 V) nanosecond pulsed conditions (pulse duration ≤10–8 ns, rise times <5 × 10–10 s) within time intervals from 1 to 8 ns. We obtained the dependence of the breakdown channel propagation velocity on gap distance using several dielectric liquids (distilled water, perfluoroeicosane, transformer oil). The experiments show that conductivity of the channel starts to rise 2–4 ns after the initiation of the breakdown. Also, the experiments show that by the moment the channel spans the gap, the conductivity increases by ∼10–30% of the initial value, i.e., when the channel starts to grow. The observed rise in conductivity is probably associated with the destruction of the channel walls caused by the ion bombardment in a strong electric field and the following impact multiplication of ions during the collisions with aggregates of atoms in the region with the gas phase.