A comparative study of Cluster observations and 3D kinetic simulations of current sheet configuration and stability in the Earth's magnetotail

G. Lapenta, W. Daughton, LANL, J.U Brackbill, P. Ricci, Dartmouth College, E. Camporeale, Politecnico di Torino

The issue of reconnection onset remains a challenge to the plasma physics community. For most physical systems of interest, reconnection does not proceed in steady manner, but rather there are periods of time in which magnetic flux is accumulated, followed by other periods in which the energy is rapidly dissipated. In current sheet geometry, one of the most well-known onset mechanisms is the collisionless tearing instability. However, for systems such as the magnetotail, it appears the tearing instability is stabilized by the magnetic geometry. Furthermore, even if the tearing mode is unstable, fully kinetic 2D simulations indicate the instability saturates at small amplitude and does not generally trigger large-scale reconnection.

Recent results from Los Alamos suggest a possible resolution to the onset problem by considering the role of current aligned plasma instabilities such as the lower-hybrid drift instability (LHDI). The nonlinear development of the LHDI leads to a variety of nonlinear modifications which can promote reconnection onset even in complex magnetic configurations such as the Earth's magnetotail. We report results of 2D and 3D kinetic simulations where the fast onset of reconnection in presence of current aligned modes is documented.