Three-dimensional current systems generated by plasmas colliding in a background magnetoplasma

Abstract

Results are presented from an experiment in which two plasmas, initially far denser than a background magnetoplasma, collide as they move across the magnetic field. The dense plasmas are formed when laser beams, nearly orthogonal to the background magnetic field, strike two targets. The merging plasmas are observed to carry large diamagnetic currents. A reconnection event is triggered by the collision and the electric field induced in this event generates a field-aligned current, which is the first step in the development of a fully three-dimensional current system. After several ion gyroperiods, the current systems become those of shear Alfvén waves. As local currents move, small reconnection “flares” occur at many locations throughout the volume, but they do not seem to affect the overall system dynamics. The data clearly show that the induced electric field is carried though the system by shear Alfvén waves. The wave electric fields as well as local magnetic helicity are discussed.