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

Abstract

Water, with its dielectric constant of epsiv=80, allows the design and construction of more compact pulse forming lines (PFLs) compared to PFLs where 'classical' dielectrics such as PTFE or other common insulators are used. With a dielectric strength exceeding 1 MV/cm gap distances can be reduced to several hundreds of micrometers, and still allow the switching of tens of kV. The small gaps allow us also to reduce the switch inductance and, consequently, to obtain high values of voltage and current rate of rise. Flowing the water through the switch at high speed allows us to remove debris and vapor bubbles left from previous shots, and to operate the switch at a high repetition rate. This work focuses on the design and operation of a compact pulsed power system with a water-filled Blumlein pulse forming line and a water switch integrated into the PFL. The pulse length of 40 ns is determined by the length of the Blumlein line, and the 10 Omega impedance by the PFL geometry and the dielectric (water). The holdoff voltage is 20 kV, and the voltage rise time is in the ns range. The pressurized water flow system used to clear the switch gap is expected to allow kHz repetition rate operation in a burst mode for several seconds