The equations of state in collisionless reconnection and their implications for the electron diffusion region
Seminar Room 2, Newton Institute Gatehouse
Wind and Cluster spacecraft observations of reconnecting current sheets in the Earth`s magnetotail show strong electron temperature anisotropy. This anisotropy is accounted for in a solution of the Vlasov equation that was recently derived for general reconnection geometries with magnetized electrons in the limit of fast transit time . A necessary ingredient is a parallel electric field structure, which maintains quasi-neutrality by regulating the electron density, traps a large fraction of thermal electrons, and heats electrons in the parallel direction. Based on the expression for the electron phase space density, equations of state provide a fluid closure that relates the parallel and perpendicular pressures to the density and magnetic field strength . This new fluid model agrees well with fully kinetic simulations of guide-field reconnection, where the parallel electron temperature becomes many times greater than the perpendicular temperature. In addition, the equations of state relate features of the electron diffusion region that develop during anti-parallel reconnection to the upstream electron beta. They impose strong constraints on the electron Hall currents and magnetic fields . For plasmas with low electron beta gradients in the anisotropic pressure can support large parallel electric fields over extended regions. This is likely important for energization of super-thermal electrons in the Earth magnetotail  and perhaps also for fast electrons observed during reconnection events at the sun.
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