Nanosecond High Voltage Pulse Generator using Water Gap Switch for Compact High Power Pulsed Microwave Generator

Abstract

Nanosecond and subnanosecond high voltage pulses can provide new applications. A cancer treatment by ultra-short pulse high electric field is one of them. High power pulsed microwave has been proposed to apply the high electric field for that treatment. This work focuses on the design of a compact high power pulsed microwave generator using nanosecond pulse power generator for the cancer treatment. To obtain fast rise time of voltage and current for nanosecond pulse, a switch has to have low inductance. A water gap switch has this property. As water has a dielectric strength exceeding 1 MV/cm, gap distances for switching can be reduced to several hundreds of micrometers, and still allow switching of tens of kV. The small gaps allow us to reduce the switch inductance. In this study, the water gap switch was built in a Blumlein pulse forming line. The Blumlein line was designed an impedance of 16 Omega for matching to an antenna and to provide 1 ns pulse. By using the water gap switch in the Blumlein line, the voltage rise time was obtained approximately 750 ps at 13 kV of peak pulse voltage. Electromagnetic wave was radiated in water by a loop antenna. A measuring antenna at 0.15 m and 0.4 m from the radiating antenna caught, respectively, electric field intensities of 116 kV/m and 32 kV/m. A frequency element of 250 MHz had highest intensity