Ignition and propagation of nanosecond pulsed plasmas in distilled water—Negative vs positive polarity applied to a pin electrode

Nanosecond plasmas in liquids are being used for water treatment, electrolysis or biomedical applications. The exact nature of these very dynamic and most important their ignition physics strongly debated. itself may be explained by two competing hypothesis: (i) via field effects (ii) electron multiplication nanovoids. Both hypothesis supported theory, but experimental data sparse due to the difficulty monitor fast processes space time. In this paper, we using camera measurements emission spectroscopy nanosecond applying a positive negative polarity sharp tungsten electrode. It is shown that plasma dominated at electrode-liquid interface either as ionization polarity. This leads hot surface temperature 7000 K polarity, whereas much lower At ignition, density reaches 4 $\cdot$ 10$^{25}$ m$^{-3}$ only 2 same time, \Ha~light times higher than During propagation, densities almost identical order 1 decay after end pulse over 15 ns. concluded propagation governed low region created nanovoids fluctuation super critical surrounding electrode pressure moment ignition.