The term runaway electrons (RE) is used to denote electrons that undergo free fall acceleration into the realm of relativistic particles. REs may be classified as thermal (lower energy) or relativistic. The study of runaway electrons is thought to be fundamental to our understanding of High-Energy Atmospheric Physics. They are also seen in tokamak fusion devices, where they can damage the reactors.
Runaway electrons are the core element of the runaway breakdown based theory of lightning propagation. Since C.T.R. Wilson's work in 1925, research has been conducted to study the possibility of runaway electrons, cosmic ray based or otherwise, initiating the processes required to generate lightning.
Electron runaway based lightning may be occurring on the four jovian planets in addition to earth. Simulated studies predict runaway breakdown processes are likely to occur on these gaseous planets far more easily on earth, as the threshold for runaway breakdown to begin is far smaller.
High Energy Plasma
The runaway electron phenomenon has been observed in high energy plasmas. They can pose a threat to machines and experiments in which these plasmas exist, including ITER. Several studies exist examining the properties of runaway electrons in these environments (tokamak), searching to better suppress the detrimental effects of these unwanted runaway electrons. Recent measurements reveal higher-than-expected impurity ion diffusion in runaway electron plateaus, possibly due to turbulence. The choice between low and high atomic number (Z) gas injections for disruption mitigation techniques requires a better understanding of the impurity ion transport, as these ions may not completely mix at impact, affecting the prevention of runaway electron wall damage in large tokamak concepts, like ITER.
Computer and Numerical Simulations
This highly complex phenomenon has proved difficult to model with traditional systems, but has been modelled in part with the world's most powerful supercomputer. In addition, aspects of electron runaway have been simulated using the popular particle physics modelling module Geant4.
Space Based Experiments
- Dwyer, Joseph R.; Smith, David M.; Cummer, Steven A. (1 November 2012). "High-Energy Atmospheric Physics: Terrestrial Gamma-Ray Flashes and Related Phenomena". Space Science Reviews. 173 (1–4): 133–196. Bibcode:2012SSRv..173..133D. doi:10.1007/s11214-012-9894-0. ISSN 0038-6308.
- Wilson, C.T.R. (1925). "The acceleration of β-particles in strong electric fields such as those of thunderclouds". Proc. Cambridge Philos. Soc. 22 (4): 534–538. Bibcode:1925PCPS...22..534W. doi:10.1017/s0305004100003236. S2CID 121202128.
- Gurevich, A.v.; Milikh, G.m.; Roussel-Dupre, R. (1992). "Runaway Electron Mechanism of Air Breakdown and Preconditioning during a Thunderstorm". Physics Letters. 165.5 (5–6): 463. Bibcode:1992PhLA..165..463G. doi:10.1016/0375-9601(92)90348-p.
- Dwyer, J; Coleman, L; Lopez, R; Saleh, Z; Concha, D; Brown, M; Rassoul, H (2006). "Runaway Breakdown in the Jovian Atmospheres". Geophysical Research Letters. 33 (22): L22813. Bibcode:2006GeoRL..3322813D. doi:10.1029/2006gl027633.
- Reux, C.; Plyusnin, V.; Alper, B.; Alves, D.; Bazylev, B.; Belonohy, E.; Boboc, A.; Brezinsek, S.; Coffey, I.; Decker, J (2015-09-01). "Runaway electron beam generation and mitigation during disruptions at JET-ILW". Nuclear Fusion. 55 (9): 093013. Bibcode:2015NucFu..55i3013R. doi:10.1088/0029-5515/55/9/093013. hdl:11858/00-001M-0000-0029-04D1-5. ISSN 0029-5515. S2CID 92988022.
- Hollmann, E.M.; Bortolon, A.; Effenberg, F.; Eidietis, N.; Shiraki, D.; Bykov, I.; Chapman, B.E.; Chen, J.; Haskey, S.; Herfindal, J.; Lvovskiy, A.; Marini, C.; McLean, A.; O'Gorman, T.; Pandya, M.D.; Paz-Soldan, C.; Popović, Ž. (2022-02-02). "Dynamic measurement of impurity ion transport in runaway electron plateaus in DIII-D". Nuclear Fusion. 29 (2): 022503. Bibcode:2022PhPl...29b2503H. doi:10.1063/5.0080385. S2CID 246504822.
- Levko; Yatom; Vekselman; Glezier; Gurovich; Krasik (2012). "Numerical Simulations of Runaway Electron Generation in Pressurized Gases". Journal of Applied Physics. 111 (1): 013303–013303–9. arXiv:1109.3537. Bibcode:2012JAP...111a3303L. doi:10.1063/1.3675527. S2CID 119256027.
- Skeltved, Alexander Broberg; Østgaard, Nikolai; Carlson, Brant; Gjesteland, Thomas; Celestin, Sebastien (2014). "Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4". Journal of Geophysical Research: Space Physics. 119 (11): 9174–9191. arXiv:1605.07771. Bibcode:2014JGRA..119.9174S. doi:10.1002/2014JA020504. PMC 4497459. PMID 26167437.