Numerical simulation of electric field enhancement at the contact of positive and negative streamers in relation to the problem of runaway electron generation in lightning and in long laboratory sparks

Abstract

The hypothetical mechanism of electric field amplification at contact of positive and negative streamers in a streamer corona up to magnitudes required for a generation of runaway electrons and secondary bremsstrahlung in the x-ray range, observed in long spark discharges in the open atmosphere, is analyzed. Development of two streamers, moving towards each other in interelectrode gaps of the centimetre range, is numerically simulated at applied voltages from 73 to 250 kV. It is shown, that the size of the domain with strong electric field with intensity sufficient for the thermal electron runaway is of 1-2 mm. The mean field intensity in this domain increases up to magnitudes ≈ 250-280 kV/cm. The maximum energy, to which electrons are capable of energizing in such field, is in the range 20-70 keV. However, the electron energy is limited by extremely small life-time of the strong field domain (less than 20 ps).