The breakdown process in an atmospheric pressure nanosecond parallel-plate discharge

The breakdown process in an atmospheric pressure nanosecond discharge with parallel-plate electrodes is investigated by temporally and spatially resolved optical emission spectroscopy (OES). The electric field is obtained from the Stark splitting of the He I 492.1 nm line. From the line ratio and a collisional-radiative model, the Te, high and Te, low (representing the effective Te in the high energy and low energy part of the EEDF, respectively) are obtained. It is found that during the breakdown process the electric field is enhanced at the ionization wave front, while it is weakened behind the wave front. This spatial profile of the electric field strongly correlates with that of both the Te, high and Te, low. The Te, high is much larger than the Te, low, which indicates that an elevated high energy tail in the EEDF is being built up under the strong electric field during the breakdown process. This argument is supported by the result from a Monte-Carlo simulation.