Self-consistent Theory of Young Plasma Bubbles: Kinetic and 3D Aspects

One of the major problems in modeling bursty transport of plasma and magnetic flux in the Earth's magnetotail is incomplete description of the elementary unit of that transport, the localized entropy-depleted flux tube or plasma bubble, which may convect much faster than the rest of the tail plasmas because of the buoyancy effect. Particularly unclear is the bubble formation process, which involves collisionless magnetic reconnection and requires therefore a non-MHD description. Recent theoretical findings, consistent with GEOTAIL and CLUSTER observations, suggest that the bubble may be treated as an earthward-moving counterpart of the plasmoid, which preserves the original tail topology, and which mimics the plasmoid outside the neutral plane due to a system of thin current sheets. Some of them are embedded into a thicker plasma sheet while others split or 'bifurcate' it. Combining 2D steady-state Vlasov models of these atypical current sheets and a modification of the theory of forced magnetic reconnection provides the self-consistent description of young plasma bubbles and gives rise to the development of the kinetic theory of bursty bulk flows. Further elaboration of this theory requires taking into account 3D effects and field-aligned currents. It also requires a kinetic modeling of the plasmoid formation in tail-like systems, which is feasible at present only with the use of open boundary conditions. In this presentation we describe a 2D kinetic model of plasma bubbles, possible 3D effects, including field-aligned currents, and the first results on particle simulations of these effects, using a new version of a massively parallelized full-particle code with open boundary conditions for both particles and fields.