The impact of angular scattering on the runaway threshold definition, consequences on the thermal runaway acceleration mechanism.

Abstract:

The discovery of Terrestrial Gamma-ray Flashes (TGFs) by the Compton Gamma-ray Observatory in 1991 is now understood as X- and Gamma-rays emissions associated with thunderstorms. This interest led to a better understanding of the emissions, now explained by bremsstrahlung from high energy electrons which run away in electric fields associated with thunderstorms. In this presentation we discuss the influence of the scattering for the runaway mechanism and the runaway threshold. We compare the outcome of different models with increasing complexity in the description of the scattering. The results show that the inclusion of the scattering in the model firstly reduces the runaway production by allowing some electrons to diffuse out of the runaway regime before they reach energy high enough to justify a forward scattering model. Secondly they affect the definition of the runaway threshold itself. We purpose a alternative definition applicable for sub-MeV electrons and discuss the impact on runaway rates.