Relativistic runaway electron avalanche

[4] RREA is unique as it can occur at electric fields an order of magnitude lower than the dielectric strength of the material.

For low-energy electrons, faster drift velocities result in more interactions with surrounding particles.

At higher energies, above about 100 keV, these collisional events become less common as the mean free path of the electron rises.

This result approximately agrees with numbers obtained from Monte Carlo simulations, of ~284 keV/cm [6] and 10 MeV,[7] respectively.

As such, after the avalanches leave the electric field region, frictional forces dominate, the electrons lose energy, and the process stops.

[10] The American physicist Joseph Dwyer coined the term "dark lightning" for this phenomenon,[11] which is still the subject of research.