PARTICLE-ACCELERATION IN A MHD SIMULATION OF MAGNETOTAIL DYNAMICS

The acceleration of protons in a dynamically evolving magnetotail is investigated on the basis of a three-dimensional resistive MHD simulation and the tracing of particles in the fields obtained from that simulation. The MHD simulation, representing plasmoid formation and ejection through a near-Earth reconnection process, generates cross-tail electric fields of up to about 4-mV/m, which lead to integrated potential differences across the tail of up to 200-kV. The large spatial extent of the increased electric field, which is largely associated with the plasma motion, together with the finite cross-tail extent suggest that acceleration might take place over a wide range of locations in x. This is confirmed by the particle tracing. An investigation of energized particles in the near-Earth region shows that these particles occupy a significant portion of the closed field line region inside of, but for moderate energies of tens of keV, not directly adjacent to, the separatrix.