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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The kinetic plasma physics of solar wind turbulence

Klein, Kristopher Gregory 01 December 2013 (has links)
As means of investigating the various mechanisms which contribute to the persistence of magnetized turbulence in the solar wind, this dissertation details the development of tools through which turbulence theories can be directly compared to in situ observations. This comparison is achieved though the construction of synthetic spacecraft time series from spectra of randomly phased linear eigenmodes. A broad overview of the current understanding of plasma turbulence through analytic theory, spacecraft observation, and numerical simulation is presented with particular emphasis on previous uses of linear eigenmode characteristics in the literature. An analytic treatment of relevant fluid and kinetic linear waves follows, providing motivation for the choice of three eigenmode characteristics for studying solar wind turbulence in this dissertation. The novel synthetic spacecraft time series method is next detailed and its use in describing magnetized turbulence justified. The three metrics are then individually employed as a means of comparing the turbulence models used to generate synthetic time series with in situ observations. These comparisons provide useful constraints on various proposed mechanisms for sustaining the turbulence cascade and heating the solar wind plasma.
2

Exploring the Alfvén-wave acceleration of auroral electrons in the laboratory

Schroeder, James William Ryan 01 August 2017 (has links)
Inertial Alfvén waves occur in plasmas where the Alfvén speed is greater than the electron thermal speed and the scale of wave field structure across the background magnetic field is comparable to the electron skin depth. Such waves have an electric field aligned with the background magnetic field that can accelerate electrons. It is likely that electrons are accelerated by inertial Alfvén waves in the auroral magnetosphere and contribute to the generation of auroras. While rocket and satellite measurements show a high level of coincidence between inertial Alfvén waves and auroral activity, definitive measurements of electrons being accelerated by inertial Alfvén waves are lacking. Continued uncertainty stems from the difficulty of making a conclusive interpretation of measurements from spacecraft flying through a complex and transient process. A laboratory experiment can avoid some of the ambiguity contained in spacecraft measurements. Experiments have been performed in the Large Plasma Device (LAPD) at UCLA. Inertial Alfvén waves were produced while simultaneously measuring the suprathermal tails of the electron distribution function. Measurements of the distribution function use resonant absorption of whistler mode waves. During a burst of inertial Alfvén waves, the measured portion of the distribution function oscillates at the Alfvén wave frequency. The phase space response of the electrons is well-described by a linear solution to the Boltzmann equation. Experiments have been repeated using electrostatic and inductive Alfvén wave antennas. The oscillation of the distribution function is described by a purely Alfvénic model when the Alfvén wave is produced by the inductive antenna. However, when the electrostatic antenna is used, measured oscillations of the distribution function are described by a model combining Alfvénic and non-Alfvénic effects. Indications of a nonlinear interaction between electrons and inertial Alfvén waves are present in recent data.

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