PhD thesis

High-energy phenomena in laboratory and thunderstorm discharges PhD thesis

Abstract: Above thunderstorms and in laboratory discharges X- and gamma-rays with energies up to tens of MeV are detected. Additionally electron beams, electron-positron beams and neutron beams are emitted from a thundercloud. We model the generation and propagation of these species using a three dimensional relativistic Monte Carlo code tracing individual particles.
In the first part of the thesis, we investigate how gamma-rays, positrons and hadrons are produced in a thundercloud from an upwards directed negative leader as a part of intracloud lightning. To relate the photon energy and direction, we integrate the Bethe - Heitler cross section for electron-nucleus Bremsstrahlung. We compare our results with cross sections used by other scientists and show that other cross sections lead to unphysically high photon energies. We model the acceleration of electrons in the leader field from some sub-eV to tens of MeV where we also include electron-electron Bremsstrahlung. We calculate the photon distribution and see that electron-electron Bremsstrahlung leads to an enrichment of electrons with energies above 100 keV and consequently to a larger number of high-energy photons. We calculate the energy distribution of positrons and hadrons. We show that a significant number of positrons with energies of up to several MeV is produced and can be detected several kilometers above their source.
The second part is motivated by work of P. Kochkin who studies the emission of X-rays from a discharge of 1 m length and 1 MV voltage. We model the motion of preaccelerated, monoenergetic electron beams with energies from 100 keV up to 1 MeV in air at standard temperature and pressure (300 K and 1 bar) and calculate the spatial and energy distribution of photons. This gives an insight into how the electron energy is transformed into photon energies.
In the third part we aim towards the understanding how high-energy cosmic rays up to 1020 eV influence lightning inception and how lightning influences measurements of cosmic rays. For such a problem, a model to trace particles from 1020 eV to sub-eV is needed. However, the range of validity of the high-energy models stops at 1 MeV when pair production does not occur anymore. Therefore we model the motion of electrons with energies from 1 keV up to 1 GeV in air at 10, 100 and 1000 mbar with and without a constant ambient electric field. We calculate the number of electrons and ions as a function of time and present the energy and spatial distribution of electrons after different time steps. We calculate that the average ionization energy per ion pair is 33 eV for 250 MeV and above. For smaller incident electron energies, however, this energy tends to 20 eV.
In the end this thesis contributes to the understanding of the generation and propagation of different high-energy species at different pressures. We give a new analysis of the production mechanisms and of the observation of beams of electrons, photons, positrons and hadrons in the atmosphere.