| Presentation Title: | Constraints on solar flare accelerated electrons and their associated return current |
| Author(s): | Meriem Alaoui, Gordon Holman, Marc Swisdak |
Abstract:
Accelerated electron beams in solar flares stream both toward the interplanetary medium and toward lower layers of the solar atmosphere where they are usually most easily observed through their hard X-ray emission. These beams constitute a current which is neutralized by a co-spatial return current, which effectively decelerates the nonthermal electron beam.
We systematically compute the electron energy distribution along the legs of a flare loop for various beam and plasma parameters relevant to solar flares, and show that interpretation of a number of flares observed with RHESSI needs to be reviewed to account for effects of return currents.
Our 1D steady-state model accounts for collisions between beam and plasma electrons, return current electric-field deceleration, thermalization in a warm target approximation, and runaway electron contributions. The results focus on the classical regime, offering a valuable benchmark for energy flux reduction and its extent.
We calculate a number of thresholds which become significant for higher nonthermal flux densities in the following order: (1) the threshold for return current losses to become energetically significant, (2) where runaway electrons become significant, and (3) where current-driven instabilities become significant, requiring a model that self-consistently accounts for them. The threshold for generating current instabilities is increased in the presence of runaway electrons. All results are dependent on beam and co-spatial plasma parameters.