Spectroscopic investigation of prebreakdown phenomena in liquid nitrogen under impulse voltage

This paper reports the results of experimental investigations about prebreakdown phenomena in liquid nitrogen, in point-plane electrode geometry (gap distance: 2 mm) under impulse voltage (up to 30 kV). As in hydrocarbon liquids, slow “bush like” streamers and fast filamentary streamers are observed in positive polarity. The spectral analysis of the emitted light during the propagation of filamentary streamers shows the second positive band emission system of nitrogen (C³II_u→B³II_g) in the region 330 nm to 400 nm. The rotational and vibrational temperature T_r and T_v can be evaluated from a comparison of experimental and simulated spectra of vibrational bands for the transition Δv=-2 of the second positive system. From these measurements, we can conclude that the temperature of gaseous filaments is about 540 K, i.e. a quite cold plasma