Ion-coupling during collisionless magnetic reconnection: causes and consequences
Date
2019
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Magnetic reconnection efficiently converts magnetic energy into particle kinetic energy. The energy release by magnetic reconnection is important for a wide range of systems, such as astrophysical, laboratory and space plasmas. The main focus of this thesis is to study and understand the magnetic reconnection phenomena found in Earth’s magnetosphere. With the aid of supercomputers and massively multi parallel particle-in-cell simulations, magnetic reconnection is explored from first-principle calculations. First, in anti-parallel reconnection, the propagation and damping of Hall magnetic fields are consistent with the linear Landau damping associated with kinetic Alfvén waves (KAW). The findings are extrapolated to the parameters observed in the Earth’s magnetotail and the solar corona and their implications are presented. Second, we perform simulations motivated by Magnetospheric MultiScale (MMS) Mission observations in the Earth’s magnetosheath. We study the coupling of ions during collisionless magnetic reconnection with simulations initialized with the parameters observed by MMS. In large guide-field and high-beta plasmas, we find that the transition from ion-coupled to electron-only reconnection is gradual as the reconnection domain size decreases. The scaling of the ion outflow velocity with exhaust width during the electron-only to ion-coupled transition is found to be consistent with a theoretical model of a newly reconnected field line. For fully ion-coupled reconnection, we find that magnetic bubble length scales of tens of ion inertial lengths are required. Third, we extend this study of electron-only reconnection to three-dimensions (3D). It is found that magnetic reconnection in 3D enhances the parallel electric field, allowing faster reconnection than the traditional 2.5D configuration. The simple Sweet-Parker scaling analysis is extended in the 3D configuration to explain the net mass flux loss in the direction perpendicular to the reconnection plane, which suggests a new and simple mechanism for the faster magnetic reconnection typically observed in the turbulent magnetosheath.