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Evolution of solar wind electrons in the inner heliosphere

Baby Abraham, Joel; (2023) Evolution of solar wind electrons in the inner heliosphere. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

In the first study, we develop and apply a novel and bespoke fitting routine to a large volume of solar wind electron distribution data collected by Parker Solar Probe (PSP) over its first five orbits, covering radial distances from 0.13 to 0.5 au. We use this database to characterize the radial evolution of the electron core, halo and strahl populations in the slow solar wind during these orbits. For the first time, we provide evidence for the growth of the combined suprathermal halo and strahl populations over the heliospheric distance range from 0.13 to 0.2 au. We find that in the inner heliosphere the formation of the halo is not solely due to the transfer of strahl electrons into the halo, which has also been previously suggested as a source mechanism for the halo at greater heliospheric distances. We find that the strahl preserves the thermal signature of the coronal origins. We discover the halo strahl cross over point. In the second study of this thesis, we develop for the first time a framework which is based on the second moment of the Boltzmann equation to evaluate the complete electron thermal energy budget. In this study, we find that there is an irreversible thermal energy source for electrons in the inner heliosphere, but the magnitude of the thermal energy source decreases with radial distance. The divergence of heat flux changes sign from positive to negative at 0.33 au. This finding indicates that there is a fundamental change in processes that define the shape of the electron distribution function at around 0.33 au. In this third study, we undertake a case study to examine the structure of the deficit signature which arises due to the ambipolar electric potential field and find that the signature is heavily processes. We find whistler driven instability is insufficient to erase the deficit signature.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Evolution of solar wind electrons in the inner heliosphere
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2023. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10184325
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