HR: 0800h
AN: NG21A-0205    [Abstracts]
TI: The sequence of self-organization of MHD plasmas
AU: * Bellan, P M
EM: pbellan@caltech.edu
AF: Caltech, 1200 E. California Blvd, Pasadena, CA 91125, United States
AB: Traditional models of plasma magnetic self-organization assume zero β on the grounds that the actual β is very small. However, a model [1] inspired by laboratory experiments suggest that the behavior of plasma with small β is not the same as a zero β \ plasma because the behavior involves a competition between β and another small parameter, namely α²a² where α=μ₀I/ψ. Here, ψ is the axial flux in the flux tube, I is the axial current flowing in the flux tube, and a is the flux tube radius. The plasma can be considered as an assembly of small aspect ratio individually pressurized flux tubes, somewhat like strands of spaghetti wrapped around each other. Each flux tube (spaghetti strand) is not force-free, but rather has its axial current I balance a small radial pressure gradient such that the pressure is peaked on the flux tube axis. To an outsider the flux tube appears as an element of force-free current because the outsider is aware that the current I in the flux tube flows parallel to the flux tube axis. The external observer makes this deduction by measuring the azimuthal magnetic field associated with the axial current. Flux tubes interact with each other by the current in one flux tube `feeling' the azimuthal magnetic field due to an adjacent flux tube. The flux tubes collectively try to assume a force-free state whereby the current in each flux tube flows parallel to the magnetic field produced by all the other flux tubes and by any external source for the magnetic field. \qquad The sequence of evolution is (i) formation of the individual plasma-filled flux tubes via axial pumping of plasma from the ends of the flux tubes to fill up the flux tubes with plasma (this process also collimates [1] the individual flux tubes so that they look like spaghetti strands), (ii) kink instability of the individual collimated flux tubes, and (iii) interaction of adjacent collimated flux tubes with each other resulting in the flux tubes wrapping around each other to be maximally force-free. Stages (ii) and (iii) involve the system relaxing to a lower-energy nearly force-free state. Experiments which demonstrate all three of the above steps will be described. \newline [1] P. M. Bellan, Why current-carrying magnetic flux tubes gobble up plasma and become thin as a result, Phys. Plasmas 10 Pt 2, 1999 (2003)
DE: 4460 Pattern formation
DE: 4485 Self-organization
DE: 7524 Magnetic fields
DE: 7831 Laboratory studies and experimental techniques
SC: Nonlinear Geophysics [NG]
MN: 2007 Fall Meeting