https://doi.org/10.1088/1361-6463/aa8519 https://doi.org/10.34657/9829 spatio temporal evolution charge carrier avalanches he singlet transitions secondary electron emission coefficients mass flow controllers gas gap width positive space charge formation collision radiation model electro optic pockels effect total flow rate discharge current maximum optical emission spectroscopy negatively charged cathodic dielectric cathodic di electric surface charge population Low Temperature Plasma Research