Understanding nonthermal particle generation, transport, and escape in solar flares requires detailed quantification of the particle evolution in the realistic 3D domain where the flare takes place. Rather surprisingly, apart of standard flare scenario and integral characteristics of the nonthermal electrons, not much is known about actual evolution of nonthermal electrons in the 3D spatial domain. This paper attempts to begin to remedy this situation by creating sets of evolving 3D models, the synthesized emission from which matches the evolving observed emission. Here we investigate two contrasting flares: a dense, coronal-thick-target flare SOL2002-04-12T17:42, that contained a single flare loop observed in both microwave and X-ray, and a more complex flare, SOL2015-06-22T17:50, that contained at least four distinct flaring loops needed to consistently reproduce the microwave and X-ray emission. Our analysis reveals differing evolution pattern of the nonthermal electrons in the dense and tenuous loops; however, both of which imply the central role of resonant wave-particle interaction with turbulence. These results offer new constraints for theory and models of the particle acceleration and transport in solar flares.
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