IGPP Seminar Series

Experiments which observe magnetic field line reconnection within structures in a Magnetoplasma

by Walter Gekelman
Department of Physics, UCLA

Abstract

Magnetic Field Line reconnection is still considered, by some, to be one of the most important topics in plasma physics. It has been in this category for close to thirty years and the “problem of reconnection” has still not been solved. Magnetic field topologies are part and parcel of the current systems within a plasma whatever their source. We present two cases in which reconnection spontaneously occurs within waves and structures embedded in a magnetoplasma. The first example is when two dense, laser produced plasmas collide in the background LAPD plasma. Complex three-dimensional currents are generated which rapidly become the currents of shear Alfvén waves. Multiple magnetic “X” points develop such as the one in the figure below. In the second case two magnetic flux ropes are generated from initially adjacent pulsed current channels .. in a background magnetoplasma. The currents exert mutual J × B forces causing them to twist about each other and merge. In addition the currents are observed to filament after merging. Volumetric space-time data show multiple reconnection sites with time-dependent locations. The quasi-separatrix layer (QSL) is a two- dimensional surface within the plasma. Two closely spaced field lines which enter the QSL wind up at very different spatial separations at finite distances along the current channel. Outside the QSL neighboring field lines remain close by. This is the first experimental measurement of a QSL. Both experiments are possible because data at tens of thousands of spatial positions in the device were acquired. Movies showing the field line and QSL development will be shown.
Tuesday, 02 June 2009
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM