HR: 16:20h
AN: SM54A-01 INVITED     [Abstracts]
TI: Three-dimensional current systems and turbulence generation by colliding plasmas in a background magnetoplasma.
AU: Gekelman, W
EM: gekelman@physics.ucla.edu
AF: University of California, Los Angeles, 1000 Veteran Avenue , Rm 15-70, Los Angeles, CA 90095-1696, United States
AU: Collette, A
EM: collette@physics.ucla.edu
AF: University of California, Los Angeles, 1000 Veteran Avenue , Rm 15-70, Los Angeles, CA 90095-1696, United States
AU: * Vincena, S
EM: vincena@physics.ucla.edu
AF: University of California, Los Angeles, 1000 Veteran Avenue , Rm 15-70, Los Angeles, CA 90095-1696, United States
AB: Results are presented from an experiment in which two plasmas, initially far denser than a background magnetoplasma (n~ 2× 10¹² cm ^-3 dia ~ 60 cm, L ~ 18m ), collide as they move across the background magnetic field (B = 600 G). The dense plasmas are formed when two laser beams, nearly orthogonal to the background magnetic field strike two carbon targets. The experiment is repeated at 1 Hz and data is acquited at 10 ns intervals and over ten thousand spatial locations. The merging plasmas are observed to carry large diamagnetic currents, which initially shield out most of the background field. A magnetic reconnection event is triggered by the collision and the induced electric field generates a field aligned current, which 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 Alfvèn waves. As local currents move, small reconnection" flares" occur at many locations throughout the plasma volume but they do not seem to affect the overall system dynamics. The data clearly show that the induced electric field is transported though the system by shear Alfvèn waves. The magnetic helicity ∫A· B dV is derived from the data and observed to grow with the Alfvèn wave currents and decay on the timescale of the wave magnetic energy. Osscillations in the helicity at the Alfvèn frequency are observed using a wavelet transfomation. Movies and data illustrating the three dimension-spacetime nature of the interaction will be presented.
DE: 7829 Kinetic waves and instabilities
DE: 7831 Laboratory studies and experimental techniques
DE: 7835 Magnetic reconnection (2723, 7526)
DE: 7836 MHD waves and instabilities (2149, 2752, 6050)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly