Mechanism Relativistic runaway electron avalanche

dynamic friction of free electrons in air compared applied electric field showing runaway electron energy range.

when electric field applied material, free electrons drift through material described electron mobility. low-energy electrons, faster drift implies higher friction drift speed tends stabilize. electrons energy above 100 kev, however, higher speeds imply lower friction. electron sufficiently high energy therefore may accelerated electric field higher , higher energies, encountering less , less friction accelerates. such electron described runaway.

as runaway electrons gain energy electric field, collide atoms in material, knocking off secondary electrons. if secondary electrons have high enough energy run away, accelerate high energies, produce further secondary electrons, etc. such, total number of energetic electrons grows exponentially in avalanche.