In some laboratory and astrophysical situations, magnetic field lines can wander chaotically in space. In the laboratory, this occurs during magnetic reconnection. Since particles follow field lines, the particle trajectories of motion can also become chaotic. In the MST experiment at the University of Wisconsin, the particle transport arising from magnetic chaos has been measured. The magnetic field and the particle motion (that appears as an electrical current) are measured by injecting lasers through the plasma. The magnetic field and current are then deduced by the effect of the plasma on the lasers (an effect known as Faraday rotation). The transport of the negative electrons and positive ions are observed to be unequal, causing an electric field to arise around the location where reconnection occurs. An implication derived from the electric field is that a strongly sheared plasma flow should arise at the reconnection location, thereby introducing the notion that chaotic magnetic fields can be a source of flow generation. Future experiments will search for such flows.
Measurement of the charge flux (or current) vs radius across a toroidal plasma, arising from the chaotic magnetic field that accompanies magnetic reconnection. (Courtesy: W. Ding, UCLA)