Dynamics of positrons during relativistic electron runaway

O. Embréus, L. Hesslow, M. Hoppe, G. Papp, K. Richards, T. Fülöp

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Sufficiently strong electric fields in plasmas can accelerate charged particles to relativistic energies. In this paper we describe the dynamics of positrons accelerated in such electric fields, and calculate the fraction of created positrons that become runaway accelerated, along with the amount of radiation that they emit. We derive an analytical formula that shows the relative importance of the different positron production processes, and show that, above a certain threshold electric field, the pair production by photons is lower than that by collisions. We furthermore present analytical and numerical solutions to the positron kinetic equation; these are applied to calculate the fraction of positrons that become accelerated or thermalized, which enters into rate equations that describe the evolution of the density of the slow and fast positron populations. Finally, to indicate operational parameters required for positron detection during runaway in tokamak discharges, we give expressions for the parameter dependencies of detected annihilation radiation compared to bremsstrahlung detected at an angle perpendicular to the direction of runaway acceleration. Using the full leading-order pair-production cross-section, we demonstrate that previous related work has overestimated the collisional pair production by at least a factor of four.

Original languageEnglish
Article number905840506
JournalJournal of Plasma Physics
Volume84
Issue number5
DOIs
Publication statusPublished - Oct 1 2018

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positrons
pair production
electric fields
radiation
kinetic equations
bremsstrahlung
charged particles
collisions
thresholds
cross sections
photons

Keywords

  • Runaway electrons

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Embréus, O., Hesslow, L., Hoppe, M., Papp, G., Richards, K., & Fülöp, T. (2018). Dynamics of positrons during relativistic electron runaway. Journal of Plasma Physics, 84(5), [905840506]. https://doi.org/10.1017/S0022377818001010

Dynamics of positrons during relativistic electron runaway. / Embréus, O.; Hesslow, L.; Hoppe, M.; Papp, G.; Richards, K.; Fülöp, T.

In: Journal of Plasma Physics, Vol. 84, No. 5, 905840506, 01.10.2018.

Research output: Contribution to journalArticle

Embréus, O, Hesslow, L, Hoppe, M, Papp, G, Richards, K & Fülöp, T 2018, 'Dynamics of positrons during relativistic electron runaway', Journal of Plasma Physics, vol. 84, no. 5, 905840506. https://doi.org/10.1017/S0022377818001010
Embréus O, Hesslow L, Hoppe M, Papp G, Richards K, Fülöp T. Dynamics of positrons during relativistic electron runaway. Journal of Plasma Physics. 2018 Oct 1;84(5). 905840506. https://doi.org/10.1017/S0022377818001010
Embréus, O. ; Hesslow, L. ; Hoppe, M. ; Papp, G. ; Richards, K. ; Fülöp, T. / Dynamics of positrons during relativistic electron runaway. In: Journal of Plasma Physics. 2018 ; Vol. 84, No. 5.
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