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Graduate Student Seminar - 10/07/2016

"Electron Energization in Guide Field Reconnection Outflows with Kinetic Riemann Simulations"

by Qile Zhang

Friday, October 7, 2016 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Professor James Drake

How electrons are heated during magnetic reconnection in the corona has been a basic puzzle for a long time. Here we carry out guide field kinetic Riemann simulations to explore electron energization, including its dependence on parameters. Riemann simulations, with their simple magnetic geometry, facilitate the study of the reconnection outflow far downstream of the reconnection point in much more detail than is possible with conventional reconnection simulations. We find that the electron temperature in the exhaust quickly increases and reaches a constant, with the heated region expanding over time. We develop a model demonstrating that the ion dynamics primarily controls the magnitude of electron heating: the ions get accelerated at rotational discontinuities, counter stream, and give rise to two slow shocks. The ions are decelerated and partially reflected at the slow shocks by electric parallel potentials, which in turn accelerate electrons and produce electron heating. The prediction of electron heating from this model is comparable to simulations. Since this model is independent of spatial scale and proton-to-electron mass ratio, the predicted electron heating in the exhaust can be expected to apply to the actual corona. Other connections to solar flare observations are discussed.

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