Electric field in APTD in nitrogen determined by EFISH, FNS/SPS ratio, α-fitting and electrical equivalent circuit model

Abstract

We investigate the electric field development in weak microseconds-lasting atmospheric pressure Townsend discharge operated in a barrier discharge arrangement in pure nitrogen. The electric field is determined using four different methods: laser-aided electric field induced second harmonics (EFISH), optical emission-based first negative/second positive systems (FNS/SPSs of molecular nitrogen) intensity ratio, electrical equivalent circuit approach and via determination of the Townsend first coefficient from the spatial optical emission profile. The resulting values of the electric field obtained by these respective methods, regardless of the differences in absolute values, lie within a reasonable range. The limitations and advantages of all methods are discussed in detail for the investigated discharge. The EFISH measurements are supported by re-computation of the effective interaction-path of the laser using an electrostatic model. The FNS/SPS method provides systematically higher values compared to other methods. We discuss in detail the potential origin of this discrepancy, as this method is at the limit of its applicability due to the low E/N values and we also consider the impossibility of full verification of the underlying assumptions. The focused discussion addresses best-practice issues and identifies possible future steps to improve each of the four methods under given conditions.