Nanosecond discharge in atmospheric air in submillimeter gaps in a uniform electric field

Abstract

A nanosecond electric discharge in air in submillimeter gaps at the overvoltages up to 15-fold is under investigation. The initial electric field in such discharges is up to 106 V/cm. This field is sufficient for the electrons that initiate the discharge, as well as those obtained during the discharge, to go into the runaway mode. These electrons are called runaway electrons (RE). REs create plasma in the period 10-9 s. When the plasma density is reached of 104 cm-3, a glow discharge (GD) is initiated. The process of transition of the discharge to the GD mode lasts 10-11 s. During this time, about 5·1010 pieces of runaway electrons are formed, which, falling on the anode, lead to the formation of an X-ray beam. This beam is due to a rapid increase in the plasma density during the discharge. In the GD stage, the electric field between the cathode and the anode is divided into two parts: the cathode layer (CL) and the plasma column. The electric field in the CL exceeds 106 V/cm. At such a field, field emission (FE) from microprotrusions on the cathode surface takes place on the cathode. It leads to the explosive emission of electrons and the formation of a cathode spot and the transition of the discharge to the arc mode.