The term runaway electrons (RE) is used to denote

electrons The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

that undergo free fall acceleration into the realm of

relativistic particle A relativistic particle is a particle which moves with a relativistic speed; that is, a speed comparable to the speed of light. This is achieved by photons to the extent that effects described by special relativity are able to describe those of su ...

s. 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 A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being ...

fusion devices, where they can damage the reactors.

Lightning

Runaway electrons are the core element of the

runaway breakdown Runaway breakdown is a theory of lightning initiation proposed by Alex Gurevich in 1992. Electrons in air have a mean free path of ~1 cm. Fast electrons which move at a large fraction of the speed of light have a mean free path up to 100 tim ...

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.

Extraterrestrial Occurrence

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 (

), searching to better suppress the detrimental effects of these unwanted runaway electrons.

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 Geant4 (for GEometry ANd Tracking) is a platform for "the simulation of the passage of particles through matter" using Monte Carlo methods. It is the successor of the GEANT series of software toolkits developed bThe Geant4 Collaboration and t ...

.{{Cite journal, last1=Skeltved, first1=Alexander Broberg, last2=Østgaard, first2=Nikolai, last3=Carlson, first3=Brant, last4=Gjesteland, first4=Thomas, last5=Celestin, first5=Sebastien, date=2014, title=Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4, journal=Journal of Geophysical Research: Space Physics, language=en, volume=119, issue=11, pages=9174–9191, doi=10.1002/2014JA020504, pmc=4497459, pmid=26167437, arxiv=1605.07771 , bibcode=2014JGRA..119.9174S

Space Based Experiments

TARANIS
(CNES)
ASIM
(ESA)

References

Particle physics