Hall currents in a current sheet: Structure and dynamics

Experimental results are presented from the study of the structure and time evolution of the Hall currents in the current sheets produced in the two-dimensional magnetic fields with the null line of the X type, in plasmas with heavy ions. Three-component magnetic fields generated by plasma currents were measured, and particular emphasis was placed on the out-of-plane magnetic field component aligned with the null line. The temporal evolution and spatial structure of the out-of-plane magnetic field and its dependence on the ion mass made us conclude that this field is produced by the Hall currents. The out-of-plane magnetic field is of the quadrupole structure, being directed oppositely on the opposite sides of the current sheet symmetry planes. The out-of-plane field exists at the initial stage of the sheet evolution, in a limited time interval, which is more prolonged for the sheets formed in plasmas with heavier ions. We revealed that the Hall currents of the opposite directions exist inside the current sheet, while the basic current has only one direction. Near the sheet middle plane the Hall currents flow from the peripheral regions toward the null line, whereas at larger distances from the middle plane the Hall currents become reversed. The Hall currents in both directions are localized only in the regions, where the basic current exists. At every time moment the oppositely directed Hall currents practically cancel each other and form four closed current circuits in the (x,y) plane, which produce the out-of-plane quadrupole magnetic field. (c) 2008 American Institute of Physics.