Physics and Astronomy Colloquium

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. The interaction spawns the generation of intense waves in the plasma. The first burst of waves observed, are whistler waves and their dispersion and spatio-temporal structure will be presented. Less than a microsecond after the collision a "magnetic reconnection" event is triggered by the collision and the electric field induced in this event generates a field aligned current. This is the first step in the development of a fully three-dimensional current system. After several ion gyro-periods the current systems become those of shear Alfven waves. As local currents move, small reconnection "flares" occur at many locations throughout the plasma volume. Magnetic field lines associated with these waves are shown in the figure above. The data clearly show that the induced electric field is carried though the system by shear Alfven waves. The relation of this experiment to phenomena in space and astrophysics will be discussed.