Date of Award
Fall 2016
Project Type
Dissertation
Program or Major
Physics
Degree Name
Doctor of Philosophy
First Advisor
Li-Jen Chen
Second Advisor
Roy B Torbert
Third Advisor
Charles J Farrugia
Abstract
How does magnetic reconnection happen in a collisionless plasma? Knowledge of electron-scale dynamics is necessary to answer this outstanding question of plasma physics. Based on fully kinetic particle-in-cell (PIC) simulations of symmetric reconnection, the spatiotemporal evolution of velocity distribution functions in and around the electron diffusion region (EDR) elucidates how electrons are accelerated and heated by the cooperating reconnection electric and normal magnetic fields. The discrete, triangular structures characteristic of EDR distributions rotate and gyrotropize in velocity space as electrons remagnetize, forming multicomponent arc and ring structures. Further downstream, exhaust electrons are found to exhibit highly structured, time-dependent anisotropies that can be used to infer the temporal stage of reconnection. Cluster spacecraft measurements from a magnetotail reconnection exhaust region agree with these simulation predictions. In PIC simulations of asymmetric reconnection, EDR distributions acquire crescent-shaped populations, indicative of accelerated magnetosheath electrons mixing with electrons of magnetospheric origin. NASA’s successfully launched Magnetospheric Multiscale (MMS) mission caught an EDR at the magnetopause and confirmed the signature crescent electron populations. A virtual spacecraft trajectory through the PIC domain is determined quantitatively by inputting MMS magnetic field measurements into an algorithm that outputs a trajectory along which the input measurements are matched. The crescent structures observed by MMS in the EDR are consistent with the simulation distributions at the corresponding time along the computed trajectory. This work demonstrates that electron characteristics can serve as “smoking-gun” observables of the EDR at the heart of the magnetic reconnection mystery.
Recommended Citation
Shuster, Jason, ""Smoking-Gun" Observables of Magnetic Reconnection: Spatiotemporal Evolution of Electron Characteristics Throughout the Diffusion Region" (2016). Doctoral Dissertations. 1363.
https://scholars.unh.edu/dissertation/1363
Movie 1.1: An ensemble of 100 pendulums governed by the nonlinear, damped, driven oscillator equation.
Movie_chapter1_2_phase_space.gif (2355 kB)
Movie 1.2: Phase space visualization of 10,000 pendulums.
Movie_chapter2_1_arc_wing_distribution.mp4 (26819 kB)
Movie 2.1: Distribution 1 of Figure 2.3 in 3D velocity space.
Movie_chapter2_2_ring_electrons.gif (11410 kB)
Movie 2.2: Test-particle tracing of the inner ring electrons' trajectories.
Movie_chapter2_3_secondary_island_distribution.mp4 (25610 kB)
Movie 2.3: Distribution 1 of Figure 2.5 from inside the secondary island in 3D velocity space.
Movie_chapter3_1_Te_evolution_Run1.gif (5545 kB)
Movie 3.1: Spatiotemporal evolution of the electron temperature during Run 1.
Movie_chapter3_2_Xline_particles.gif (17911 kB)
Movie 3.2: Test-particle tracing forward in time for the striations of the triangular X-line distribution.
Movie_chapter3_3_Xline_2256_particles.gif (4693 kB)
Movie 3.3: Backward and forward test-particle tracing for 2,256 electrons from the X-line distribution.
Movie_chapter3_4_inflow_electrons.gif (10139 kB)
Movie 3.4: Fragmentation of inflow distributions.
Movie_chapter3_5_electron_holes.gif (689 kB)
Movie 3.5: Electron holes along the separatrix.
Movie_chapter3_6_electron_encyclopedia_Run1.gif (2613 kB)
Movie 3.6: Spatiotemporal evolution of Run 1 from a kinetic electron's perspective.
Movie_chapter4_1_trajectory.mp4 (17550 kB)
Movie 4.1: Virtual MMS spacecraft trajectory through the simulation domain.
Movie_chapter4_2_crescent_distribution.mp4 (17191 kB)
Movie 4.2: Crescent distribution from the EDR in 3D velocity space.