Title : How does a co-spatial return current affect solar flare accelerated electrons?
Speaker Name: Meriem Alaoui Abdallaoui Speaker Institution : Goddard Space Flight Center
Abstract : Solar flares rapidly and efficiently accelerate a tremendous number of electrons at the tops of coronal loops. These energetic electrons then propagate both toward the interplanetary medium and toward the lower and denser solar atmosphere. Over the course of the electrons’ transport, a co-spatial counter-streaming return current is induced, thereby balancing the current density. In response to the return current electric field, a fraction of the ambient electrons will be accelerated into the runaway regime. I will present a model in which an accelerated electron beam drives a steady-state, sub-Dreicer co-spatial return-current electric field, which locally balances the direct beam current and freely accelerates a fraction of background (return-current) electrons. The model is self-consistent, i.e., the electric field induced by the co-evolution of the direct beam and the runaway current is considered. I will show how return currents affect the atmospheric thermal response to an injected electron beam, X-ray observations and the acceleration/injection region. The results depend on the injected beam flux density, the temperature and density of the background plasma. Specifically, I will show that (1) the return current electric field can return a significant number of suprathermal electrons to the acceleration region, where they can be further accelerated to higher energies, runaway electrons can be a few tens of percent of the return current flux returning to the nonthermal beam’s acceleration region, (2) the energy gain of the suprathermal electrons can be up to 10−35 keV, (3) the heating rate in the corona can be reduced by a factor of three for medium range injected fluxes in comparison to models which neglect the runaway component.