The critical avalanche of runaway electrons

Abstract

The x-ray and gamma-ray flashes observed in the Earth atmosphere during a thunderstorm are usually associated with the generation of runaway electrons (RE) in atmospheric electric fields. It is supposed that runaway electron avalanches initiated by cosmic rays play the main role in high-altitude discharges observed in a thunderstorm atmosphere. We have performed three-dimensional numerical calculations to investigate the mechanism of the development of a critical avalanche and to determine its parameters. It has been shown that the number of electrons in a critical avalanche occurring in air under conditions characteristic of thunderstorm discharges can reach a value of the order of 10 18 .

Estimation of number of runaway electrons per avalanche in Earth's atmosphere

“…A recent paper [7] presents the results of the 3D Monte-Carlo simulation of runaway avalanche development. The paper is focused on the avalanche-to-streamer transition.…”

“…The paper is focused on the avalanche-to-streamer transition. One of the main results of [7] is the estimation of the (a) E-mail: timuruh@mail.ru (b) E-mail: nozik.aa@mipt.ru (c) E-mail: egrstadnichuk@yandex.ru (d) E-mail: svechnikova@ipfran.ru (e) E-mail: mihail.zelenyy@phystech.edu number of electrons in one avalanche: 10 17 -10 18 . The value is significantly larger than values presented in other simulations [8][9][10], which show about 10 6 fast electrons and 10 10 slow electrons per avalanche in normal conditions (air pressure, gas composition, etc.).…”

“…-A more accurate estimation of characteristic length of runaway electron avalanche could be obtained using GEANT4 transport code [12][13][14], a standard tool for Monte-Carlo simulation in high energy physics (in this work we use version 4.10.05). The particle propagation mechanism used in GEANT4 is quite different from the one used in [7]. GEANT4 uses particle tracks describing trajectories each particle and its descendants.…”

“…GEANT4 uses particle tracks describing trajectories each particle and its descendants. The simulation in [7] uses particle population evolution in time. The evolutionary approach is useful for low-energy particle and plasma dynamics but usually is not used for precise simulation of high energy particles.…”

“…2. One of the main reasons behind the simulation approach in [7] is to limit otherwise very large simulation time and memory footprint. GEANT4 in general shares the same problem, but allows us to set an upper limit by calculating only multiplication length in Gurevich model.…”