Framework of unified nonequilibrium plasma model and collisional-radiative model for characterisation of microdischarges in metal vapours of Cd and Zn

Abstract Direct current microdischarges in metal vapours of cadmium and zinc occurring during contact separation in a test apparatus related to explosion protection were investigated and compared in detail. Their characterisation was done in a framework that combined a unified nonequilibrium plasma model and a collisional-radiative model (CRM). The plasma model provided the basic plasma parameters (number densities of ground state neutral and singly charged species and their energies, electric field, discharge voltage). Number densities of excited atomic states were obtained on a second stage employing a CRM and the already known plasma parameters. This modelling framework allowed one to obtain spatially and temporally resolved plasma parameters and the population of the excited atomic states in the entire discharge gap during the separation of the electric contacts. The modelling work was supported by electrical measurements, high-speed imaging and optical emission spectroscopy. The experimental findings enabled the calibration of the plasma model with respect to the discharge voltage and a qualitative and to some extent quantitative comparison of computed and measured spectral intensities.