dc.contributor.advisor | Spanier, F.A. | |
dc.contributor.advisor | Bottcher, M. | |
dc.contributor.author | Ivascenko, Alex | |
dc.date.accessioned | 2017-08-23T09:22:50Z | |
dc.date.available | 2017-08-23T09:22:50Z | |
dc.date.issued | 2016 | |
dc.identifier.uri | http://hdl.handle.net/10394/25425 | |
dc.description | PhD (Space Physics), North-West University, Potchefstroom Campus, 2017 | en_US |
dc.description.abstract | The transport of charged particles in turbulent plasma is a crucially important area of
research in astrophysics, since it directly impacts our ability to interpret observations
done with a major group of messenger particles. In order to understand these measurements
of highly energetic charged particles - or cosmic rays - a comprehension of
their interactions with the turbulent magnetic fields, which permeate the heliosphere,
the interstellar and the intergalactic medium, is equally important as the understanding
of their generation and acceleration at the sources, if not more so.
In this work, a numerical approach is taken to derive transport parameters for charged
energetic particles in the heliosphere. A spectral incompressible MHD code is used to
generate realistic turbulence in a self-consistent way. The properties of the turbulence
are then probed by injecting test particles and analysing their propagation. New numerical
analysis methods, that were developed to work especially well in strong turbulence
scenarios, where classical methods and analytical solutions fail, are presented, together
with their validation and transport parameter results obtained for various simulation setups.
In most astrophysical scenarios the magnetic field fluctuations can be assumed to
be much larger than the fluctuating electric fields δB >>δE, consequently the predominant
transport process is the change of the direction of the particle momentum relative
to the magnetic field - or pitch angle - as opposed to the change of the absolute value
of the momentum p, which is suppressed in comparison. Hence, the focus of the analysis
is on the pitch angle diffusion coefficient Dµµ. To demonstrate that the concept can also
be applied to other quantities, results for the perpendicular spacial diffusion coefficient
D┴ are derived and presented as well.
Additionally, an alternative method to generate turbulence in magnetised plasmas using
Perlin gradient noise is described and its characteristics concerning particle transport
are analysed and compared with the self-consistent MHD-turbulence in order to test its
validity. Although the properties of the Perlin noise turbulence are not in complete
agreement with MHD, the deviations can be neglected in specific cases (especially in
strong turbulence) and are offset somewhat by the much lower computational effort. | en_US |
dc.language.iso | en | en_US |
dc.publisher | North-West University (South Africa), Potchefstroom Campus | en_US |
dc.subject | Diffusion | en_US |
dc.subject | Heliosphere | en_US |
dc.subject | Magnetohydrodynamics (MHD) | en_US |
dc.subject | Numerical simulation | en_US |
dc.subject | Particle transport | en_US |
dc.subject | Scattering | en_US |
dc.subject | Turbulence | en_US |
dc.title | The nature of diffusive particle transport in turbulent magnetic fields | en_US |
dc.type | Thesis | en_US |
dc.description.thesistype | Doctoral | en_US |
dc.contributor.researchID | 24420530 - Bottcher, Markus (Supervisor) | |
dc.contributor.researchID | 25161814 - Spanier, Felix Alexander (Supervisor) | |