Experimental and numerical investigation of nanosecond discharges in air gap with hemispherical dielectric layer

Electrical discharges are transient phenomena highly sensitive to the geometric and dielectric properties of their surrounding environment. Such a dependence directly influences plasma-surface interactions and the efficiency of the application. This study investigates experimentally and by simulation the propagation dynamics of nanosecond discharge in air gap with the presence of a hemispherical dielectric layer (HDL). Experimentally, the HDL was fabricated using 3D printing of opaque resin that has a dielectric permittivity ε_r = 3. Its diameter and thickness can be finely adjusted during printing. Herein, we investigate the influence of HDL’s thickness (100-1000 µm) on the dynamics of the discharge generated inside and outside of the HDL using an ICCD camera. To further determine the spatial and temporal properties of the discharge, numerical simulations are performed by adapting a 2D fluid model [1]. The simulation predicts the spatial evolution of electrons density and electric field inside and outside of the HDL. After being validated for the experimental cases, the model is employed to investigate the role of ε_r (3, 40, 80) on the discharge properties. The results offer new insights for understanding plasma-surface interactions which is highly needed for many applications.