Reduction of the downward energy flux of non-thermal electrons in the solar flare corona due to co-spatial return current losses

Non-thermal electrons accelerated at the top of solar flare magnetic arcades carry a substantial fraction of the flare energy and, therefore, impact the evolution of flare plasma and its radiation signatures. The energy flux they carry into the chromosphere can be estimated from both the evolution of the flare hard X-ray spectrum and the comparison of hydrodynamic models with observations of flare chromospheric and coronal line emission. Relating this flux to the flux accelerated in and escaping from the region at the top of the flare arcades, however, depends on knowing how much this energy flux may have been altered when the electrons propagated through the corona. A co-spatial return current that maintains charge neutrality and current stability reduces the energy flux of the non-thermal electrons. This poster examines the significance of this energy flux reduction. We present a systematic study of the various regimes of the return current for a wide range of electron beam parameters appropriate for the solar flare case. Our model is 1D and includes the effects of binary collisions between the non-thermal electrons and ambient return-current electrons. It includes the electric-field deceleration of particles, thermalization of the non-thermal electrons in a warm-target approximation, and the contribution of runaway electrons to the return current. The results are restricted to the classical regime. They provide a convenient reference for when the energy flux reduction is significant and an estimate of the extent of the reduction.