Authors: Jeongbhin Seo (LANL), Fan Guo (LANL), and Xiaocan Li (Dartmouth)

Solar flares are among the most dramatic events in solar and space physics, releasing a substantial amount of magnetic energy and consequently accelerating electrons to energies ranging from a few keV to tens of MeV. Observations at multiple wavelengths, including hard X-ray (HXR), microwave, and gamma-ray, have clearly shown emission signatures of nonthermal particles. Spectral analysis of these nonthermal emissions in certain flare events has suggested efficient acceleration in the solar flare region. Recent observations have revealed that the above-the-looptop region may be the most important site for confining nonthermal electrons. Several studies suggest that a significant fraction of released magnetic energy is used to generate nonthermal electrons. However, it is still unclear how the underlying energy release and efficient particle acceleration and transport occur. To estimate the number density and energy density of nonthermal electrons, we have developed a new method for magnetohydrodynamic simulation that includes the back reaction from nonthermal electrons. Our findings show that magnetic energy is dissipated into both thermal and nonthermal particle energy. In the above-the-looptop region, nonthermal electrons exhibit a power-law distribution, as expected from observations. Specifically, we find that the slope of the energy spectrum becomes steeper when the injected fraction of nonthermal electrons increases. We find it is typical that the fraction of nonthermal electron energy to magnetic energy is about 50% in the above-the-looptop region.