SPRG Seminars
October 18, 2011:
" Laboratory Access to the Physics of Magnetosphere and Astrophysical Plasmas
"
Thomas Intrator, Los Alamos National Laboratory, New Mexico
Shocks and magnetic reconnection are two grand challenge topics that are difficult to model in the laboratory. Several experimental approaches are described, that derive from our Magnetized Target Fusion (MTF) efforts at Los Alamos, and a smaller tabletop device.
SHOCKS: We have designed a shock piston driver that takes advantage of a theta pinch Field Reversed Configuration (FRC) plasma injector for MTF. Cosmically relevant, collisionless, magnetized shock parameters are accessible, including Reynolds number Re=1e6, magnetic Reyolds number Rm=5000, sonic mach number Ms=100, Alfven mach number MA=20. Shocks from large laser experiments are typically not magnetized, so that this dynamically accelerated FRC provides a unique experimental platform.
MAGNETIC RECONNECTION: There is a growing consensus that the Sweet-Parker presumption that stable reconnecting current sheets are stable is a fatal flaw in the argument. We now believe that large aspect (width to thickness) ratio current sheets spontaneously disrupt into smaller spatial domains, magnetic islands, or plasmoids, or flux ropes in 3D. Hierarchies of micro scale structures densely distributed down to kinetic scales are predicted, with rapid magnetic flux diffusion and reconnection rates. Archaeological excavations of the world wide FRC database reveal data relevant to reconnection of wide and thin current sheets at large Lundquist numbers S>1e6. These represent the only laboratory example extant that addresses the currently hotly debated question of whether reconnecting current sheets are intrinsically unstable or not. A small LANL experiment provides flux rope shredding data and is gearing up to do the current sheet problem. A collaboration to investigate the island-plasmoid-flux rope hierarchy could take advantage of spacecraft observations, lab experiments and large simulations.