ИСТИНА

Thin current sheets (TCSs) with characteristic scale of a spatial inhomogeneity about proton gyroradii are widespread structures in space plasma. They are usually observed in different cosmic systems from individual planetary magnetospheres to the whole heliosphere. TCSs are shown to be responsible for the storage of the excess of magnetic energy and its consequent fast release during magnetic reconnection processes that are followed by particle thermalization, wave activity and intense plasma flows along magnetic field lines. We proposed the simple analytical theoretical model of the embedded TCSs equilibrium where the thinnest current sheet supported by electron curvature drifts is embedded inside the thicker proton-dominated sheet where protons go along specific serpentine-like trajectories with small jumps of quasi-adiabatic invariants during separatrix crossings. Our model allows estimating the self-consistent thickness of the embedded electron sheet within the surrounded proton sheet. It is shown that the electron sheet scaling in TCS has a universal character for all collisionless plasma. Current sheet stability is estimated in a frame of a linear perturbation theory. It is shown that the electron sheet embedding plays a principal role in TCS destruction. The comparison with experimental MMS observations is made. Thus very compact MMS spacecraft constellation is favorable for the investigation of electron scale current sheets (CSs). During magnetotail CS crossings in 2017 - 2019 MMS revealed several tens intervals when very intense (J ~ several tens of nA/m^2) electron CSs were observed. The half thickness of such CSs is ~ 100 km or less which is much smaller than the proton gyroradius. In many cases the electron CSs were observed during the propagation of fast earthward or tailward flows. We have analyzed the spatial structure of electron CSs and found the presence of nonlinear electron scale current structures indicating on the possible metastable state of the CS.