Electric field measurements on plasma bullets in N2 using four-wave mixing

Atmospheric pressure plasma jets generated by kHz nanosecond voltage pulses typically consist of guided streamer discharges called plasma bullets. In this work, plasma bullets are generated in a pulsed plasma jet using N-2 as feed gas and their electric field distribution is investigated by polarization-resolved four-wave mixing. The method and its analysis have been extended to resolve radial profiles of non-uniform, but radially symmetric, electric field distributions. In addition, a calibration procedure using an electrode geometry different from the discharge geometry has been developed. A radially resolved profile of the axial electric field component of a plasma bullet in N-2 is presented, as well as the temporal development of the (line-integrated) radial and axial components of the electric field. To verify the results, they are compared to a streamer model adapted to the conditions of the experiment. The peak values obtained from the experiment are in the range expected from streamer literature. However, there are some quantitative differences with the model, which predicts values approximately a factor two lower than those found in the experiment, as well as a faster radial decay. The temporal development shows similar features in both the experiment and the model. Explanations for these differences are provided and further improvements for the method are outlined.