On the Ring-Shaped Structure of Helium Plasma Jets

The results of simulation of positive streamers propagating along plasma jets formed in pure helium and in helium with 3% of air and emerged into ambient air are presented. It is shown, in agreement with the experimental data, that the addition of air leads to disappearance of ring-shaped structure of plasma jet radiation typical to jets of pure helium. The calculated radial profiles of the electron density in channels of streamers propagating in air at nonuniform radial distributions of the gas density are also given. Like in plasma jets, these profiles can have a ring-shaped structure. In both cases, the reason for the formation of ring-shaped structure is radial nonuniformity of the rate of ionization of gas species by electron impact.