LAUSR

The discharge of a charged dielectric in low pressure air has characteristics that resemble some of the features of mesospheric discharges. The dielectric discharges in steps when the pressure of the surrounding air is gradually reduced from nearly atmospheric to ~0.01 torr. The set-up employed here decouples the discharge from the power supply and, thanks to that, unique properties of the discharge manifest themselves. For example: in the pressure interval ~10-100 torr streamers are emitted from the surface of the dielectric but when the pressure decreases to 2-16 torr these are replaced by spherically symmetrical discharges that we call peonies. These have interesting properties, like: a) they do not produce electrical field, b) they remain static and c) their size increases with decreasing pressure. The peonies are a type of discharge that has not been reported before. They resemble sprite beads and are assumed to consist of large avalanches that do not lead to the formation of a streamer. At further lower pressures, in the interval 0.01-0.1 torr, diffuse volume discharges were observed that have some morphological similarities with sprite halos and the top of columnar sprites. The spectrographic measurements carried out show that the discharges have bands from the first and second positive system in N2 as well as lines of N2+. Quenching of the first negative system of N2 was observed at 3 torr. In this work it was also observed how a cosmic ray can go on to trigger a discharge inside the experimentation chamber.