Nanosecond pulsed discharge in high density polymer liquid (PDMS)

Summary form only given. Generation of discharges in water has been previously investigated, with formation mechanisms being attributed to ionization of vapour within bubbles formed through localized heating or cavitation, and within which plasma is sustained¹. More recently, the possibility of plasma formation in liquid phase in the absence of bubble formation has been reported, with experiments performed in liquid water². This work reports the generation of non-equilibrium nanosecond discharges in liquid phase without bubbles. We studied the effects of dielectric properties of the liquid, discharge gap, and electrode size. In our experiments we compared discharges ignited in liquid water and PDMS, a comparatively non-polar liquid with dielectric constant of 2.3 and three orders of magnitude higher viscosity than water. Nanosecond high voltage pulses (+15.5 kV) with ∼2 ns rise times and 12 ns duration are applied to submerged electrodes arranged in a pin-to-plate geometry, with the positive potential applied to the pin with radius of curvature of 5 um and 20 um. The positive polarity of the pin rules out electron emission as a mechanism for plasma formation. Time resolved images of the plasma discharge are achieved down to 2 ns exposure resolution using the 4picos high-speed camera, demonstrating the filamentary structure of the plasma. The effects of dielectric properties of liquid and electrode diameter on plasma discharge size and lifetime are demonstrated to be negligible. Shadowgraphy and spectroscopy studies are also performed and reported.