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Thesis (Ph.D.) - University of St Andrews, May 2010.

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Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

The upper atmosphere of the sun, the solar corona, is approximately 1,000,000K hotter than the surface of the Sun, a property which cannot be explained by the normal processes of heat conduction and radiation. It is now commonly believed that the magnetic fields which fill the solar atmosphere, and propagate down into the interior of the Sun, are important for transferring and transforming energy from the strong plasma flows inside the Sun into the corona as heat. I have investigated an elementary flux interaction which forms a fundamental building block of the coronal heating process. This interaction involves two opposite polarity sources on the Sun's surface in the presence of an overlying magnetic field. To fully understand how this interaction transfers heat into the solar corona, the magnetic skeleton is required, which shows possible sites of heating that are due to magnetic reconnection. A magnetic field is best described by its magnetic skeleton. The most important parts of the magnetic skeleton to find are the null points, from which separatrix surfaces extend that divide magnetic flux of different topology. Part of this thesis proposes a new method of finding null points, for which the accuracy is shown and then compared with another commonly used method (which gave false results). Using these techniques for finding the magnetic skeleton in the magnetic interaction above, the evolution of the skeleton was found to head through seven distinct states, some of which were far more complicated than expected. This included a high number of separators (the intersection of two separatrix surfaces), which are a known location of magnetic reconnection. This separator reconnection was shown to be the main heating mechanism in this interaction, from which the total amount and rates of reconnection in the experiment was calculated. This led to the discovery of recursive reconnection, a process where magnetic flux is reconnected before reconnecting back to its original state, to allow for the process to repeat again. This recursive reconnection was shown to allow far more reconnection than would have been previously expected, all of which releases heat into the neighbouring areas of the atmosphere. Finally, the interaction was modelled with sources of different magnetic radii but of equal flux. This showed that when the antisymmetric nature of the previous interactions was removed, there was little change in the reconnection rates, but when the strength of the overlying magnetic field was increased, the reconnection rates were found to increase. This increase in the overlying magnetic field strength also produced a new magnetic feature called a bald-edge, which was found to replace some of the null points. These bald-edges were found to be associated with surfaces similar to separatrix surfaces that divide flux of different topology but do not extend from a null point. Also features similar to separators extend from these bald-edges.

No description available.

A recently proposed set of demagnetization diagnostics [Scudder et al., submitted to Physics of Plasmas, 2015] is related to the preconditions of Guiding Center Theory (GCT) and benchmarked in kinetic particle-in-cell simulations. Specifically, GCT requires that the time and length scales of the field are long compared to the Larmor motion of the particles. When this condition is violated, the particles become demagnetized and the assumptions of magnetohydrodynamics are no longer valid. In this thesis, these diagnostics are applied to different space plasma layers of different length scales. In the past, proxy diagnostics that are not based on fundamental GCT conditions have been used to search for, and provide evidence of, demagnetization in different space plasma layers. The problem with these proxy diagnostics is that they are not invertible to demagnetization. The diagnostics presented in this thesis are not only unique to demagnetization, but also have the additional advantages of being dimensionless, scalar, and independent of coordinate system. These diagnostics are applied to three space plasma layers of different length scales, resulting in new insights and methods for detecting particle demagnetization. First, the evidence for wave heating in the solar wind is reexamined through its fundamental assumptions of demagnetization. The proxy diagnostic commonly used for demagnetization is non-conservation of the Chew-Goldberger-Low conserved quantity. This diagnostic is a good proxy for the first adiabatic invariant in the supersonic regime. To test this and compare it to the assumptions of the Helios analysis [Marsch et al., Journal of Geophysical Research: Space Physics, 88(A4), 1983], the solar wind is modeled through a self-consistent Vlasov mapping. In addition, other experimental assumptions in that same Helios analysis are also examined. Second, a new method for estimating local length scales is demonstrated across a known bow shock crossing. This new method, based on one of the demagnetization diagnostics, is different from current methods in that it can be performed with single spacecraft data and does not require a special coordinate system. Third, a new set of invertible signatures of the electron diffusion region (EDR) is introduced and applied to five magnetopause events to search for layers of collisionless magnetic reconnection. Four of these magnetopause events have not been identified before in the literature. The five EDR diagnostics are large electron pressure anisotropy, non-perturbative GCT expansion parameters, order one electron pressure agyrotropy, and order one electron thermal mach number. These EDR diagnostics are compared to a wide range of degenerate diagnostics that are commonly used in reconnection studies. The results of this analysis show that, compared to these degenerate diagnostics, the EDR diagnostics are much more surgical in their identification of electron-scale current layers.

Thesis (Ph.D.)--University of Waikato, 2007. / Title from PDF cover (viewed May 12, 2008) Includes bibliographical references (p. [168]-175)

Thesis (Ph. D.)--University of Iowa, 2008. / Thesis supervisor: William Daughton. Includes bibliographical references (leaves 202-207).

Thesis (Ph.D.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Richard Canfield. Includes bibliographical references (leaves 83-88).