Measurement of electron density in transient spark discharge by simple interferometry

Abstract In this work, the electron density in an atmospheric-pressure Ar transient spark (TS) discharge was measured using an interferometric method. The discharge was operated in a pin-to-plate electrode configuration by applying DC voltages of 7–10 kV. The TS discharge current occurred within a short duration of less than 100 ns, and the peak current was as high as ~ 3 A. Below 8 kV, the TS discharge had weak, irregular emission, making it difficult to measure the electron density using Stark broadening. Here, we developed a simple He–Ne laser Michelson interferogram method for estimating the electron density of unstable TS discharge. Above 8 kV, the electron density values obtained from Stark broadening and the Michelson interferogram were similar and proportional to the dissipated energy. This interferogram method could be adopted to measure the electron density of unstable discharge plasmas, which was measured to be 1 × 1016 cm−3 at 7.0 kV in this experiment.