Nanosecond-pulsed discharge in cryogenic liquids

In this work we report the results of imaging and spectroscopic measurements of the optical emission spectra of nanosecond-pulsed cryogenic discharge ignited in liquid nitrogen and argon. We studied both polarities of the discharge and demonstrate that while with the application of a relatively low electric fields the negative polarity discharge appears as a faint glow around the high-voltage needle electrode, application of the electric fields above transition values results in the discharge mode switch to a negative in-liquid streamer which closely resembles the positive streamers. The structures of both positive and negative streamers, their sizes (~1-3 mm), and the propagation velocities (∼500 km s⁻¹) exhibit remarkable similarity.

Broadened argon lines allow estimations of the densities of the neutrals in the main body of the discharge with corresponding values on the order of few tens of atmospheres, which in conjunction with the reduced electric field evaluations performed in liquid nitrogen suggests electric field values of around 6-8 MV/cm. Overall, our experimental results indicate that both positive and negative discharges in liquid argon develop via streamer mechanism directly in the liquid phase.