The effect of photoemission on nanosecond helium microdischarges at atmospheric pressure

TL;DR

This study uses particle-based simulations to explore how VUV resonance radiation influences helium microdischarges at atmospheric pressure, revealing photon-induced electron emission effects that alter discharge behavior.

Contribution

It introduces a detailed simulation approach including VUV photon transport and resonance effects, highlighting their impact on microdischarge characteristics at atmospheric pressure.

Findings

VUV photons significantly modify discharge characteristics.

Photon trapping and escape times are longer than pulse durations.

Electron emission from cathode due to VUV photons enhances plasma density.

Abstract

Atmospheric-pressure microdischarges excited by nanosecond high-voltage pulses are investigated in helium-nitrogen mixtures by first-principles particle-based simulations that include VUV resonance radiation transport via tracing photon trajectories. The VUV photons, of which the frequency redistribution in emission processes is included in some detail, are found to modify remarkably the computed discharge characteristics due to their ability to induce electron emission from the cathode surface. The electrons created this way enhance the plasma density and a significant increase of the transient current pulse amplitude is observed. The simulations allow the computation of the density of helium atoms in the 2$^1$P resonant state, as well as the density of photons in the plasma and the line shape of the resonant VUV radiation reaching the electrodes. These indicate the presence of significant radiation trapping in the plasma and photon escape times longer than the duration of the excitation pulses are found.