Modeling helps fill knowledge gap in plasma-in-liquid streamer physics

Plasmas in liquids are used for water treatment, plasma medicine, and plasma-supported electrolysis, among other applications. Usually, they are generated by high voltage metal electrodes inside the liquid, with the applied voltage pulsed to prevent its constant boiling. When ignited, the plasma propagates like a lightning strike through the medium. In plasma physics, these structures are called streamers if they do not reach the grounded electrode. For nanosecond voltage pulses, the exact physical processes of streamer ignition and propagation are not yet fully understood.

To address this knowledge gap, Jüngling et al. compared velocity and dynamics of plasma propagation with modeling to analyze individual mechanisms and transport coefficients. Their research employed intensified charge-coupled device (ICCD) imaging to investigate the time dependence of streamer dynamics compared to a 1D fluid code for negative voltages.

“Due to the short time scales, it’s challenging to gain information on the physics from experiments, so modeling approaches are necessary,” said co-author Katharina Grosse. “Our paper presents experimental results on streamer velocities and lengths, from which we deduce physical processes relevant to streamer propagation.”

The researchers found streamers can be characterized best by the balance between ionization and recombination at the so-called streamer head. They concluded that other mechanisms, such as advection and diffusion, can be neglected, and that the streamer dynamics are independent of the sign of the electric field, which differs from streamers in gases.

“The exact ignition and propagation mechanisms also tune the chemistry in the liquid. Therefore, it is important that we understand the streamer physics better,” said Grosse.

Source: “Propagation of nanosecond plasmas in liquids - streamer velocities and streamer lengths,” by E. Jüngling, K. Grosse, and A. von Keudell, Journal of Vacuum Science & Technology A (2022). The article can be accessed at http://doi.org/10.1116/6.0001669 .

This paper is part of the Atmospheric Plasma-Liquid Interfaces, learn more here .