Ionization Mechanism in a Thermal Spark Discharge

Abstract

The formation of thermal sparks generated by nanosecond pulses is studied experimentally and numerically. The increase of the electron number density, up to 10 19 cm -3 , is measured with sub-nanosecond resolution using Stark broadening of N + , Stark broadening of Hα, continuum emission of the electron, and the intensity of N + lines. Our experimental results are then compared to 0-D kinetic simulations including the electron-impact ionization of excited electronic states of N and O. The electron temperature, in equilibrium with the gas temperature, reaches 42,000K, which agrees with our experimental findings and the literature on the thermal spark.

Simulation of ionization-wave discharges: a direct comparison between the fluid model and E-FISH measurements

“…Once the streamer approaches the ground, there is a very strong field between the ionization head and the cathode. Once the ionization head touches the end, the repulsion of the electric field leads to a further increase in the electron density, and if the electric field in the channel is strong enough to ionize the gas, the electron density grows sharply and a non-equilibrium discharge may even transform into a thermal spark [9,10].…”

“…A simple way of generating low-temperature plasmas at moderate and high pressures is to use high-voltage electrodes separated by a gaseous gap. However, the original cold plasma could rapidly become a strongly conducting junction that evolves into a thermal spark [9,10], where heavy species tend to be in equilibrium with electrons at a few tens of thousands degrees Kelvin, leading to a huge amount of energy consumption and the destruction of chemical species. One way to prevent this temperature equilibrium between heavy species and electrons is to use nanosecond pulsed discharges (NPD), which are usually produced by a short-duration, high peak voltage at the electrodes.…”