MIPSE Seminar

Three-Dimensional Magnetic Field Line Reconnection Involving Flux Ropes and Alfvén Waves

Professor Walter GekelmanUniversity of California-Los Angeles

We report on experiments investigating 3D magnetic
field line reconnection, a phenomenon in which
the magnetic field energy is converted to particle energy
and heating accompanied by changes in magnetic
topology. In the first experiment two magnetic flux
ropes are generated from adjacent pulsed current
channels in a background magnetoplasma in the Large
Plasma Device (LAPD). The currents exert mutual J  B
forces causing them to twist about each other and
merge. The currents move towards or away from each
other and filament after merging. Volumetric spacetime
data show multiple, time dependent reconnection
sites. We also observed the quasi-separatrix layer
(QSL), a narrow region between the flux ropes. Field
lines on either side of the QSL have closely spaced
foot-points at on end of the flux ropes, but a different separations at the other end. Outside the
QSL, neighboring field lines do not diverge. In the second experiment 3D currents associated with
colliding laser produced plasmas in the background magnetoplasma are observed. The currents
are those of shear Alfv én waves. The wave fields are small fractions of the background field; nevertheless,
reconnection regions, multiple magnetic “X” points and a QSL are all observed. These
results imply that magnetic field line reconnection is not an independent topic, but part of the phenomena
associated with the broader subject of 3D waves and current systems in plasmas.
Dr. Walter Gekelman is a Fellow of the American Physical Society and professor in
the Dept. of Physics and Astronomy at UCLA. His BS was from Brooklyn College and Ph.D. from Stevens
Institute of Technology. At UCLA Gekelman has developed three plasma devices, each progressively larger
and more sophisticated to solve problems at the frontier of basic plasma physics. These have culminated in
the Large Plasma Device (LAPD), the premier machine for basic plasma studies, yielding important insight
into basic processes observed in space by rockets and spacecraft. Gekelman pioneered the use of computer
visualization techniques in plasma physics to elucidate the complex 3D structures that are hidden in
very large data sets.

Sponsored by

Michigan Institute for Plasma Science and Engineering