SPRG Seminars
October 09, 2012:
"Electron energization and wave dispersion in a mirror kinetic Alfven wave"
P. Damiano, Princeton Plasma Physics Laboratory, Princeton, NJ
Alfven waves in which mirror force effects dominate the parallel electric field generation can be termed mirror kinetic Alfven waves (Nakamura, JGR, 2000). Examples can be global scale Alfven waves (Field Line Resonances) that stand along the Earth's closed dipolar magnetic field lines and have been observationally linked to the formation of some auroral arcs. We use a hybrid MHD-kinetic model, that self-consistently couples the cold plasma MHD equations to a system of kinetic guiding center electrons, to explore the characteristics of these global modes. It is found that mirror force effects self-consistently result in parallel potential drops sufficient to accelerate electrons to keV energies (in order to carry the field aligned current) and the wave energy dissipated in this acceleration can damp the wave in a few Alfven cycles. In conjunction with the acceleration, there is also a structuring in the temporal evolution of the electron energization that scales with the electron bounce frequency and a cross-scale coupling from the global driver to kinetic scales that fragments the parallel current region. The perpendicular Poynting flux associated with the parallel electric field disperses wave energy perpendicular to the magnetic field leading to a broadening of the parallel current region as electrons are accelerated along adjacent field lines. For ambient plasmasheet electron temperatures, this mirror force induced dispersion dominates over that associated with electron inertial effects.