Algebraic electron beam operations for reconstructing runaway electron energy spectrum

Abstract:

Runaway electrons are the essential building blocks in the emerging field of high-energy atmospheric physics. Electrons can be accelerated into the runaway mode through the strong electric fields that exist around the tip of lightning channels. Due to the probabilistic and dangerous character of lightning it is difficult to evaluate this process in nature. For this reason, we investigate results of laboratory experiments where the source location of runaway electrons, their subsequent X-ray emissions, and the electrical discharge properties can be easily pinpointed. In this work, we use Geant4 Monte Carlo simulations to characterize the X-ray emissions associated with runaway electrons in centimeter-long laboratory discharges, mirroring the setup in a previous experimental investigation [da Silva et al., GRL, 44, 11174, 2017]. We perform a series of simulations with monoenergetic electron beams varying their initial kinetic energy and number of electrons in the beam, allowing us to determine the fundamental response of the system. Furthermore, we introduce a methodology to perform algebraic operations with electron beams to allow one to reconstruct any desired electron energy spectrum. Finally, we reconstruct the energy spectrum of runaway electrons from measurements of their X-ray emissions in centimeter-long streamer discharges.