On the Electrons Dynamics during Rapid Island Coalescence in Asymmetric Magnetic Reconnection: Case With and With No Guide Field

Abstract:

We present a set of fully kinetic 2.5D simulations of electron dynamics during rapid magnetic islands coalescence in asymmetric conditions. Simulations are performed using the massively parallel fully kinetic implicit moment method code iPIC3D (Markidis et al. 2010). The domain is a double periodic box with two current sheets initially representing two different reconnection conditions with the same asymmetric ratio. In the upper sheet the conventional hyperbolic continuous functions for magnetic field and density are initialised across the layer (e.g. Pritchett 2008). In the lower layer the same asymmetric conditions are used the presence of an extremely steep gradient describing a pure tangential discontinuity.
Cases with and without guide field are compared.

While the upper layer shows the typical reconnection evolution of an asymmetric configuration, the lower layer very soon develops not-uniformly distributed multiple reconnection points which rapidly evolve in a series of magnetic islands. Quick islands coalescence follows.

Even though the electrons dynamics during island merging has been studied in both symmetric and asymmetric conditions (e.g. Pritchett 2007, 2008b, Drake et al. 2006, Oka et al. 2010, Huang et al. 2014), these simulations show new interesting features such as the presence of three distinct regions, here named X, M and D, with very different properties. Regions X and M manifest typical signatures of ongoing reconnection, distinguishable thanks to the direct comparison with the outcomes of the upper layer. In particular, M-type regions are different because reconnection occurs between two merging islands in a vertical fashion with respect to the direction of the current sheets initially set. In contrast, regions D present a quite diverse features, not showing the typical signatures of a occurring reconnection.

The present work is supported by the NASA MMS Grant NNX08AO84G. Additional support for the KULeuven team is provided by the European Commission DEEP-ER project, by the Onderzoekfonds KU Leuven (Research Fund KU Leuven) and by the Interuniversity Attraction Poles Programme of the Belgian Science Policy Office (IAP P7/08 CHARM). The simulations were conducted on the computational resources provided by the PRACE Tier-0 2013091928 (SuperMUC supercomputer).