Instabilities of the magnetotail current layer in hybrid-Vlasov simulations of the Earth’s magnetosphere.

 On the macroscale, the large-scale magnetic field structure governs the magnetotail current layer. At the same time, it must be supported by the self-consistent dynamics of charged particles. While the current layer reaches a critical state, microscale processes start to play a leading role by triggering kinetic instabilities. These instabilities drive changes in large-scale magnetic topology and particle energization.

 This study examines the instabilities of the Earth's magnetotail current layer using global hybrid-Vlasov simulations (Vlasiator). In our simulation, the southward interplanetary magnetic field causes dayside reconnection which leads to the accumulation of magnetic flux on the night side and the magnetotail current sheet thins down to ~5 proton inertial lengths. The current layer undergoes reconnection accompanied by the formation of multiple X-lines initiated by tearing instability. During the formation of the X-lines, we observe crescent-shaped proton velocity distributions as the signature of resonance interaction of the demagnetized population with the reconnection electric field. The tearing instability manifests as the filamentation of the electric current, appearing as a chain of plasmoids extending along the Sun-Earth direction. Fourier analysis of the perturbed electric current reveals a tearing growth time on the order of ~40 proton gyroperiods for plasmoids with a characteristic size of ~30 skin depths. 

 As the tearing instability evolves, the kinking of the current layer gets more prominent on the duskward side of the tail. The kink instability leads to the excitation of the flapping-type waves developing across the tail. The wavelength of the flapping oscillations is ~ 15 proton skin depths, and the growth time is ~80 proton gyroperiods. The active thermalization of the crescent-shaped proton distributions is associated with the development of kink instability.