| Summary: | We have developed an empirical electrical-breakdown relation that can be used to design large-area water-insulated pulsed-power systems. Such systems often form an integral part of multiterawatt pulsed-power accelerators, and may be incorporated in future petawatt-class machines. We find that complete dielectric failure is likely to occur in water between a significantly field-enhanced anode and a less-enhanced cathode when E_{p}τ_{eff}^{0.330±0.026}=0.135±0.009. In this expression E_{p}≡V_{p}/d is the peak value in time of the spatially averaged electric field between the anode and cathode (in MV/cm), V_{p} is the peak voltage across the electrodes, d is the distance between the anode and cathode, and τ_{eff} is the temporal width (in μs) of the voltage pulse at 63% of peak. This relation is based on 25 measurements for which 1≤V_{p}≤4.10 MV, 1.25≤d≤22 cm, and 0.011≤τ_{eff}≤0.6 μs. The normalized standard deviation of the differences between these measurements and the associated predictions of the relation is 12%.
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