Space and time resolved characterization of a He-N2 RF atmospheric pressure plasma jet by E-FISH measurements and PIC/MCC simulations

Abstract

An atmospheric pressure radiofrequency (RF) plasma jet operated in a He/N2 gas mixture is investigated experimentally by electric field induced second harmonic generation measurements of the spatio-temporal electric field and by phase resolved optical emission spectroscopy measurements of the excitation rate, as well as computationally, using the particle-in-cell/Monte Carlo collisions approach. The experimental and computational results show a very good quantitative and qualitative agreement for the electric field and reveal its time-dependent behavior at various locations within the electrode gap. This agreement also validates the simulation model, which allows the computation of several additional discharge characteristics. Some of them, namely the space- and time-resolved electron density, the time-averaged spatial profiles of the electron and ion densities, the electron absorbed power as well as the conduction and displacement current densities, are compared with the values derived from the spatio-temporal electric field measurements. The agreement obtained between these quantities points out the usefulness of laser based methods of electric field measurements that can be accomplished with high spatial and temporal resolution. Last, but not the least, we show experimentally and numerically that the RF jet is non-quasi neutral on time average across the whole discharge gap.