Dissertation
Characterizing the signatures of electron Landau damping throughout the inner heliosphere
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2023
DOI: 10.25820/etd.007283
Abstract
A long-standing goal in the heliophysics community is to understand the mechanisms of particle energization that dissipate turbulent energy in the weakly collisional plasma of the solar wind. One mechanism that is thought to play a major role is Landau damping, though the extent to which it contributes to turbulence dissipation in the solar wind remains unclear. Despite decades of study, the small length scales and fast time scales at which these mechanisms operate make them difficult to simulate or observe \emph{in situ}. Recently, however, Landau damping by electrons became the first of the many proposed turbulence dissipation mechanisms to be observed using the field-particle correlation technique. This recently developed method uses single-point observations of electromagnetic fields and particle velocity distribution functions to reveal velocity-space signatures of particle energization that are distinct to the various dissipation mechanisms. Motivated by the first \emph{in situ} observation of Landau damping in Earth's magnetosheath, the goal of this thesis is to characterize signatures of particle energization via electron Landau damping under solar wind conditions in order to develop a more complete understanding of how this mechanism may be observed. We do this by generating high-resolution, gyrokinetic simulations of plasma turbulence and applying the field-particle correlation technique to the simulation data. First, we perform a case-study analysis to corroborate the observed field-particle correlation signature of electron Landau damping by generating a simulation of magnetosheath plasma turbulence. Next, we consider how signatures of electron Landau damping vary throughout the inner heliosphere by using a suite of four gyrokinetic turbulence simulations with varying plasma-$\beta$. Finally, we demonstrate the ability of the field-particle correlation technique to recover velocity-space signatures of resonant Landau damping when the frequency of the damped \Alfven wave is above the Nyquist frequency of the spacecraft. Since this occurs even for modern spacecraft like the \emph{Magnetospheric Multiscale Mission} and \emph{Parker Solar Probe}, we develop a rule-of-thumb model for using field-particle correlations to recover \emph{in situ} signatures in under-sampled conditions. Our results expand existing theory on identifying electron Landau damping in the heliosphere and create context for future applications of the field-particle correlation technique to spacecraft data.
Details
- Title: Subtitle
- Characterizing the signatures of electron Landau damping throughout the inner heliosphere
- Creators
- Sarah A. Conley
- Contributors
- Gregory G Howes (Advisor)Jasper S Halekas (Committee Member)Allison N Jaynes (Committee Member)Frederick Norman Skiff (Committee Member)Kristopher Klein (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Spring 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007283
- Number of pages
- xv, 154 pages
- Copyright
- Copyright 2023 Sarah A. Conley
- Language
- English
- Date submitted
- 04/24/2023
- Date approved
- 04/27/2023
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (pages 136-154).
- Public Abstract (ETD)
The observed temperatures in the plasma of the Sun’s atmosphere (the corona) and in the tenuous stream of supersonic particles that flow from the Sun through the solar system (the solar wind) are hotter than expected. One source of this unexplained energy is turbulence in the solar wind flow. When the turbulent eddies are dissipated at small scales, the energy they contain is transferred to particles as heat or acceleration. Though the physical mechanisms responsible for this transfer are not pinned down, one option involves resonant particles ‘surfing’ on the turbulent eddies in a process is known as Landau damping. Recently, by using a method called the field-particle correlation technique that can distinguish between dissipation mechanisms by revealing their unique, mechanism-specific signatures, Landau damping became the first turbulence dissipation mechanism to be observed in space. Motivated by this discovery, we perform high-resolution simulations of solar wind plasmas in order to characterize the field-particle correlation signature of electron Landau damping and how it changes throughout the solar system. Additionally, because electron Landau damping occurs in the solar wind for high frequency waves, we explore the ability of the field-particle correlation technique to reveal energization signatures in data with low time resolution compared with the wave frequencies. Our results will help identify electron Landau damping in current and future spacecraft missions, which will clarify the role of this mechanism in dissipating turbulent energy and heating the solar wind.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984424790802771
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