Численное исследование возможности генерации убегающих электронов в формирующемся катодном слое самостоятельного объемного разряда высокого давления

Calculations of the formation of the cathode layer of an self-sustained high-pressure volume discharge with pre-ionization of the gas medium excited by nano-and subnanosecond voltage pulses are carried out. It is shown that at pressures of ~ 1 atm at the final stage of the cathode layer formation, conditions for the generation of escaping electrons arise. We also considered the transition of electrons into runaway mode from the area of electric field amplification in front of the plasma (streamer) channel, which originates from the top of the micro-spike on the cathode. It is shown that at pressures of ~ 10 atm, electrons can transfer into runaway mode immediately after emission from the top of micro-spike in amplified electric field. Thus obtained runaway electrons can create pre-ionization of the gaseous medium and provide the formation of the initial phase of the discharge in volume form in the system without external pre-ionization.

On Refining the Criterion for a Single Avalanche-tо-Streamer Transition in Air in Strong Uniform Electric Fields

The article presents the results from mathematical modeling of avalanche-to-streamer transitions in an air discharge gap. The electric field is uniform with the strength E0=50--70 kV/cm, and the atmospheric conditions are standard. The consideration is limited to single avalanche-to-streamer (SATS) transitions. The moment of time corresponding to the plasma streamer channel incipience is taken as the transition moment. As a result of the SATS transition, a two-headed streamer is generated. First, its negative anode-directed head is formed from the avalanche. After that, its positive cathode-directed head emerges from the avalanche track. Behind it, the field strength decreases to a critical value at which effective impact ionization is impossible. The streamer plasma channel occurs earlier, in the negative head incipience process. When it appears, effective ionization still continues between the avalanche and its track. The critical number of electrons in the avalanche, which is determined by the time the channel appears, depends weakly on the E0 value if the avalanche-streamer transition occurs far from the electrodes. In this case, it is about 30 million. If the transition occurs near the electrodes, this number lies in the range from 40 to 50 million particles.

SURFACE DISCHARGE SIMULATION IN SF6 AND N2 MIXTURES WITH A PLASMACHEMICAL MODEL

SF 6– N 2 mixtures are becoming the best alternative for SF 6 in electrical systems. Plasmachemical modeling and the results of a positive surface streamer are reported in this paper. The model exhibits excellent streamer transition from the gas gap to the insulator surface. The surface charge accumulations on the dielectric insulators are compared and discussed. Results showed that the density of negative ions is much larger than that of electrons in the surface streamer channel. The dominant [Formula: see text] and less pronounced [Formula: see text] constitute the main negative ions in the electronegative surface streamer because of the strong electron attachments to SF 6 molecules.

Ozone Production by Primary and Secondary Streamers in Pulsed Positive Corona Discharge

The energy efficiencies of ozone production by the primary and secondary streamers are studied in pulsed positive corona discharge. In a 20-kV dry air discharge, the two-dimensional distribution of ozone density shows that most of ozone is distributed in the secondary streamer channel, not in the primary one. It demonstrates that most of ozone is produced by the secondary streamer. However, the energies consumed by the primary and secondary streamers are estimated to be approximately equal in the 20-kV discharge. This result indicates that the energy efficiency of ozone production by the secondary streamer is much higher than that by the primary one. It is shown that high voltage operation is favorable for ozone production because the rise in voltage increases the ratio of energy consumed by the secondary streamer to that consumed by the primary one.