A compact, nanosecond pulse generator with water as dielectric and as switch medium

A pulse charged 10 ns Blumlein type pulse generator with distilled water as dielectric in the pulse-forming network (PFN), and as switch medium was built and tested. The use of water with its large relative dielectric constant, and consequently high-energy storage density allows us to reduce the size of the PFN considerably, compared to PFNs using solid dielectrics. The impedance of the PFN, a strip line consisting of two aluminum bars was 10 /spl Omega/, but can easily be varied by changing the distance of the metal lines. With an electrode separation of as small as 200 /spl mu/m of the water spark gap, maximum voltages of 15 kV could be applied. In order to determine the limitations of the water switch in a repetitively operated system, switch delay, jitter and recovery time were measured. The delay and jitter were found to be both in the range of a few microseconds for an electric field of 700 kV/cm in the water gap, but were reduced to a few hundred nanoseconds when the electric field was increased to 850 kV/cm. The recovery time was found to vary from 1 ms to 6 ms. Consequently, the maximum reliable repetition rate for switch using static water is 150 Hz. However, because of the extremely small size of the active switch volume, use of flowing water promises to allow higher repetition rate operation.