Dartmouth Events

Abstract: Magnetic Reconnection is a ubiquitous phenomenon in plasma, where magnetic energy is released into plasma thermal and kinetic energy through the rearrangement of magnetic topology. In this study we derive fluid scaling models to predict the steady state and onset behavior of magnetic reconnection in the highly magnetized (relativistic) regime, in the presence of plasma shear flows and a (out-of-plane) guide field. We use 2.5D kinetic particle-in-cell simulations to motivate and validate these models. %analytical and numerical models in fluid frameworks.
We find that, similar to the non-relativistic regime, shear flows parallel to the reconnecting magnetic field will delay reconnection onset and slow outflow jets. They can also cause asymmetry and rotation in the the diffusion region. 
We derive a scaling model for the outflow speed using a steady state force balance, including relativistic effects, and the motional electric field which can be large in relativistic plasma. Unlike in the non-relativistic limit, the addition of a guide field lowers the in-plane Alfv\'en velocity, contributing to slower outflow jets and more efficient suppression of reconnection.
To model the onset time of reconnection we develop a numerical eigen-solver for the growth rate of relativistic linear tearing instability. We find slowing of growth due to both shear flows and guide field, consistent with the delay in onset observed in simulations. We also find at higher shear flow speed, a transition through an intermediate regime to linear Kelvin-Helmholtz instability, which can also be responsible for inducing reconnection. Additional effects on morphology of the diffusion and the composition of the reconnection electric field due to the guide field and shear flow are discussed. An understanding of the dynamics and onset conditions of reconnection is important to space weather, control of terrestrial plasma and explaining astrophysical observations.

Graduate Advisor: Associate Professor Yi-Hsin Liu

Zoom Link: https://dartmouth.zoom.us/j/91705161690