Energy cascades in large-scale solar flare reconnection

Abstract

Very fast energy release is sometimes observed in large-scale current layers formed in astrophysical plasmas. Solar flares represent a clear example. The dissipation and changes of the magnetic field topology in the almost collisionless plasmas are inherently related to plasma-kinetic processes in very thin current sheets (CSs). Question arises, how the originally thick current layer is efficiently fragmented into these small-scale dissipative CSs. We investigated this question by means of high-resolution MHD simulations. In addition to the earlier considered chain plasmoid instability we identified other elementary process for energy transport from large to small scales – fragmenting coalescence of plasmoids. This result changes so far basically 1D picture of energy cascade in a large scale magnetic reconnection and reveals multi-dimensional nature of the fragmentation process. At the same moment it shows that plasmoid coalescence contributes – quite surprisingly – to the direct energy cascade.