Influence of the angular scattering of electrons on the runaway threshold in air

O. Chanrion, Z. Bonaventura, A. Bourdon, T. Neubert

Research output: Contribution to journalJournal articleResearchpeer-review

228 Downloads (Pure)

Abstract

The runaway electron mechanism is of great importance for the understanding of the generation of x- and gamma rays in atmospheric discharges. In 1991, terrestrial gamma-ray flashes (TGFs) were discovered by the Compton Gamma-Ray Observatory. Those emissions are bremsstrahlung from high energy electrons that run away in electric fields associated with thunderstorms. In this paper, we discuss the runaway threshold definition with a particular interest in the influence of the angular scattering for electron energy close to the threshold. In order to understand the mechanism of runaway, we compare the outcome of different Fokker–Planck and Monte Carlo models with increasing complexity in the description of the scattering. The results show that the inclusion of the stochastic nature of collisions smooths the probability to run away around the threshold. Furthermore, we observe that a significant number of electrons diffuse out of the runaway regime when we take into account the diffusion in angle due to the scattering. Those results suggest using a runaway threshold energy based on the Fokker–Planck model assuming the angular equilibrium that is 1.6 to 1.8 times higher than the one proposed by [1, 2], depending on the magnitude of the ambient electric field. The threshold also is found to be 5 to 26 times higher than the one assuming forward scattering. We give a fitted formula for the threshold field valid over a large range of electric fields. Furthermore, we have shown that the assumption of forward scattering is not valid below 1 MeV where the runaway threshold usually is defined. These results are important for the thermal runaway and the runaway electron avalanche discharge mechanisms suggested to participate in the TGF generation.
Original languageEnglish
Article number044001
JournalPlasma Physics and Controlled Fusion
Volume58
Issue number4
Number of pages9
ISSN0741-3335
DOIs
Publication statusPublished - 2016

Bibliographical note

Original content from this work may be used under the terms of the Creative commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Keywords

  • Terrestrial gamma-ray flashes
  • Runaway electrons
  • Streamers
  • Thunderstorms
  • Angular scattering
  • Lightning
  • Thermal runaway

Fingerprint

Dive into the research topics of 'Influence of the angular scattering of electrons on the runaway threshold in air'. Together they form a unique fingerprint.

Cite this