Date of Degree
PhD (Doctor of Philosophy)
Scudder, Jack D.
First Committee Member
Baalrud, Scott D.
Second Committee Member
Gurnett, Donald A.
Third Committee Member
Fourth Committee Member
Merlino, Robert L.
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 When this condition is violated, the particles become demagnetized and the assumptions of magnetohydrodynamics are no longer valid.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.
The solar wind from the sun is a hot ionized gas called plasma. This plasma contains charged particles that are bound to the magnetic field lines of the sun. Under certain conditions, these charged particles can be freed from their magnetic field lines. This process is called demagnetization and can occur when the solar wind collides with the earth’s magnetic field. At this interface of collision, particles that are demagnetized from the sun’s magnetic field can become re-magnetized onto the earth’s magnetic field, a process called collisionless magnetic reconnection. In this thesis, a method for identifying reconnection events is tested for the first time on measurements from the Polar spacecraft. This method is based on theoretical requirements for demagnetization and can be used to study particle demagnetization in other types of space plasma structures as is also demonstrated in this thesis.
publicabstract, Heliophysics, Magnetic Reconnection, Magnetopause, Plasma
xviii, 223 pages
Includes bibliographical references (pages 210-223).
Copyright 2015 Jershon Ysrael Lopez
Lopez, Jershon Ysrael. "Demagnetization diagnostics in collisionless space plasma layers." PhD (Doctor of Philosophy) thesis, University of Iowa, 2015.