Fine structure of  thin current sheets

L.M. Zelenyi

Thin current sheets(TCS) -remarkable almost singular layers of very concentrated currents 
have been found in  a number of recent spacecraft experiments . Kinetic theory explains
 many features of such sheets including their thickness of the order (or less) of ion Larmor
 radius, their possible bifurcations and occasionally appearing very thin sublayers of a 
 strong electron currents. Simulations indicate on a possibility of ion current reversal in  a center of 
TCS structure. Phase space of ion component is distinctively partitioned on  trapped , quasitrapped
 and transient domains.  Stochastic diffusion  of  mostly non-adiabatically moving ions results
in the gradual  exchange of population between these domains. This process facilitates relatively slow
evolution of the sheet towards the marginal state. Possibility of a catastrophic scenario of TCS 
disruption is also discussed.