Dc point-to-plane discharge in pure oxygen in the 50-760 Torr pressure range

The present work is a part of a general study dealing with pure gases at pressures in the 50-760 Torr range. This experimental study concerns discharges occurring in oxygen, between a curvature radius rhodium point and a stainless steel plane 1 cm distant. A positive dc high voltage is applied to the point using a 0-30 kV, 0-10 mA power supply. Electrical measurements are performed so that voltage-current characteristic curves can be drawn for the whole pressure range. Current impulses are recorded at the earthed plane in each typical regime of the discharge. These electrical impulses are compared with the simultaneous optical signals obtained from a photomultiplier. A focalization on the photomultiplier of various precise spots in the interelectrode gap allows one to get some information about the propagation of an ionizing front from the high-voltage electrode to the grounded plane. From comparison with previous studies, it may be inferred that the glow regime is more difficult to visualize on the characteristic curves than it is in the case of nitrogen. However, `streamer-like' impulses are observed for oxygen in the whole pressure range, which is not the case for nitrogen. The continuity between these streamer-like impulses and the `classical' streamers observed at atmospheric pressure seems to be established and confirms the important role played by electronegativity in the inception of ionizing fronts.