Particle Acceleration and Transport during 3D CME Eruptions

Abstract

We calculate particle acceleration during CME eruptions using combined magnetohydrodynamic (MHD) and test-particle models. The CMEs are generated via the breakout mechanism and both 2D and 3D MHD configurations are investigated. In this scenario, reconnection at a "breakout" current sheet (CS) above the CME flux rope initiates the eruption by destabilizing a quasi-static force balance. Reconnection at the flare CS below the erupting flux rope drives the fast acceleration of the CME, and forms flare loops below as well as producing the particle acceleration observed in flares. We present test-particle calculations that focus on two selected times during the impulsive and decay phases of the eruption and obtain particle energy gains and spatial distributions. We find that particles are accelerated more efficiently in the flare CS than in the breakout CS even in the presence of large magnetic islands. This result has important implications for particle acceleration in coronal jets. The maximum particle energy gain is estimated from the energization terms based on the guiding-center approximation. Particles are first accelerated in the CSs (with or without magnetic islands) where Fermi-type acceleration dominates. We find that, as expected, accelerated particles precipitate into the chromosphere along the flare loops, or become trapped in the flare loop top due to the magnetic mirror structure, but some energetic particles escape to interplanetary space along

Stochastic Electron Acceleration by Temperature Anisotropy Instabilities Under Solar Flare Plasma Conditions

“…This implies that an anisotropic 'loss-cone' electron velocity distribution (with T e,⊥ > T e, ) naturally forms within the looptops (e.g., Fleishman et al 1998). In addition, the contraction of the looptops in this model also increases the T e,⊥ > T e, anisotropy via the betatron process, which tends to amplify the electron momentum perpendicular to B (Karlicky et al 2004;Minoshima et al 2010;Grady et al 2012;Filatov et al 2013;Xia et al 2020). From the observational point of view, the presence of a T e,⊥ > T e, anisotropy in the looptops is supported by the inferred trapping of microwave emitting electrons in these regions (Melnikov et al 2002), and also as an ingredient for the occurrence of radio spike bursts in these environments (Fleishman et al 1998(Fleishman et al , 2003.…”

“…In solar flares, the pitch-angle scattering provided by electron temperature anisotropy instabilities is believed to play an active role in controlling both the T e,⊥ > T e, anisotropy as well as the electrons ability to precipitate from the contracting looptops to the footpoints of the flares (Minoshima et al 2010(Minoshima et al , 2011Xia et al 2020). We study the effect of this scattering in producing stochastic acceleration of electrons making use of 2D particle-in-cell (PIC) simulations.…”