Electric field measurements in a He:N2 nanosecond pulsed discharge with sub-ns time resolution

Abstract

The electric field in the He:N2 nanosecond atmospheric pressure plasma jet is studied using the electric-field induced second harmonic generation technique. It is shown that the calibration obtained with a DC voltage applied to the discharge cell may lead to incorrect results in the electric field measurements. It is proposed to use nanosecond high voltage pulses at low repetition rates for the calibration instead of a DC voltage. The temporal development of the electric field in the discharge at different distances from the cathode is measured with high temporal (100 ps) and spatial (50 µm) resolution. An electric field profile structure similar to the one in streamers or ionization fronts is observed. The velocity of the propagation of the falling edge of the ionization front is determined to be 0.85 × 106 m s−1. The validity of the local field approximation, important for modeling of these kind of discharges, is confirmed for the present conditions based on time and space derivatives of the measured electric field. The temporal evolution of the electron density is obtained by the measured electrical current and the time resolved electric field measurement combined with the electron mobility calculated with BOLSIG+.