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 10^{20} eV influence lightning inception and how lightning influences measurements of
cosmic rays. For such a problem, a model to trace particles from 10^{20} 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.