  In this work we report the results of imaging and spectroscopic measurements
of optical emission spectrum of negative nanosecond-pulsed cryogenic discharge
in liquid nitrogen. With the application of lower electric fields, the
discharge first ignites as a 'faint glow' around the high voltage needle
electrode, while when the applied electric field reaches transition value of
around 5 MV cm-1, the discharge mode switches to negative in-liquid streamer.
Optical emission spectrum of the discharge is populated by the molecular
nitrogen emission bands, and their analysis shows that the pressures and
temperatures of the negative streamers in liquid nitrogen are at least of few
tens of atmospheres and around 140-150 K. The results of the study demonstrate
similarity of positive and negative streamers in the cryogenic in-liquid plasma
conditions.
