Optical measurements of the electric field of pulsed streamer discharge in water

Nanosecond and sub-nanosecond high voltage pulses can provide new applications. A cancer treatment by an ultra short pulse high electric field is one of them. High power pulsed electromagnetic wave has been proposed to apply the high electric field for that treatment. This work focuses on the design of a compact high power pulsed electromagnetic wave generator for the cancer treatment. The experimental setup consists from a pulse transformer, a pulse completion circuit and an L-C inversion circuit. We employed the L-C inversion circuit for the pulsed power generator to obtain a voltage waveform with single frequency for applying an antenna. A water gap switch and a water capacitor were used for the L-C inversion circuit to obtain the frequency of hundreds MHz, because the water gap switch has a low inductance property and the loop inductance of the circuit can be made small using the same medium for the capacitor and the switch. Water is a high permittivity of about 80 and a high dielectric strength of more than 1 MV/cm. That allow for energy densities greater than 3J/cm³. By using the water gap switch and the water capacitor for the L-C inversion circuit, the pulsed voltage had the frequency element of 250 MHz. This experiment measured electrical field of between a needle and a plate for the water gap switch for optical system. The optical system was used for detecting the Kerr effect of water.