RESISTIVE PHASE OF A HIGH-VOLTAGE WATER SPARK

The resistive phase of self-breaking water-dielectric spark gaps in a high-current relativistic electron-beam accelerator is investigated experimentally. For gaps that withstand voltages V?1.8 MV and mean electric fields between 2×107 and 5×107 V/m, both the current rise time and the energy dissipated in the discharge are adequately described by the semiempirical relations of Martin. In contrast to the results reported in lower-energy experiments, no evidence was found of a slowly varying resistive phase with a gap resistance comparable to the circuit impedance after t=2.5τr. Approximately 8±3% of the energy dissipated in the gap is coupled into a shock wave generated by the discharge. Light emission from the arc channels indicated that the light was strongly filtered by the highly excited water surrounding the channel, and the light emission cannot be analyzed to determine the plasma properties of the arc channel unambiguously.