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Progress and Plans on Magnetic Reconnection for CMSO For NSF Site-Visit for CMSO May1-2, 2005 1. Experimental progress [M. Yamada] -Findings on two-fluid physics 2. Theoretical progress [E. Zweibel] -Effects of global boundary conditions 3. Summary and Research Plans

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Magnetic Reconnection Topological rearrangement of magnetic field lines Magnetic energy => Kinetic energy Key to stellar flares, coronal heating, particle acceleration, star formation, energy loss in lab plasmas * A key question: Why does reconnection generally occur so fast? Before reconnectionAfter reconnection

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Major Goals for Magnetic Reconnection in CMSO (1) Study 2-fluid effects in the reconnection region and determine the role of fluctuations. (2) Find key relationships between the local physics of the reconnection layer and the dynamics of global reconnection, including boundary conditions. (3) Develop universal parameter scalings for reconnection applicable both space and laboratory plasmas 4) Evaluate the role of magnetic reconnection in dynamos, ion heating, and, more generally, in other magnetic self-organization phenomena.

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Four devices [MRX, MST, SSX, and SSPX] are available for reconnection research in CMSO MRX SSX MST SSPX Experiments are supported by numerical modeling and theory

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Fast Reconnection Enhanced Resistivity Main question –What is the cause of the observed enhanced resistivity? Hall MHD Effects create a large E field Electrostatic Turbulence Electromagnetic Fluctuations »All Observed in CMSO experiments

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Two Models to Fast Magnetic Reconnection Generalized Sweet-Parker model with anomalous resistivity. Presence of EM fluctuations Two-fluid MHD model in which electrons and ions decouple in the diffusion region (~ c/ pi ). V in V out » V a

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Two types of reconnection layer profiles observed in MRX High density collisional regime Low density collisionless regime

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Experimentally measured 3-D field line features in MRX Manifestation of Hall effects in MRX: Out-of-plane quadrupole field Electrons pull magnetic field lines with their flow

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The Electron Flow Profile is Measured Good agreement between the measurement and the simulation (yellow region). MeasurementSimulation A MRX high resolution probe array ( R = 2.5 mm) shows electron flow patterns to create an out-of-plane QP field (EM fluctuation present)

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Mozer et al., PRL 2002 POLAR satellite Striking similarities with the the data from the magnetopause ~ c/ pi EM & ES fluctuation profiles are very similar

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MRX scaling shows transition from the MHD (collisional) to 2 fluid regime based on normalized ion skin depth MRX Scaling: A linkage between space and lab on reconnection Breslau d i / sp ~ 5( mfp /L) 1/2

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Quadrupole out-of-plane field has been reported by SSX push reconnection experiment Ion inertial scale 2 cm

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Hall term is also strong in MST Determining reconnection rate and E field Hall dynamo peaks at resonant surface but is spatially extended (8 cm ~ c/ pi ) Ding,et al PRL,93,045002(2004) Hall Term

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Multiple reconnection leads to strong dynamo effects Left: Core m=1 tearing mode only Right: Edge m= 0 mode driven by core mode Strong ion heating is observed with multiple reconnection Two cases of sawtooth relaxation

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Interplay between local and global effects Effects of line tied boundary conditions on kink mode & current sheet formation Scalings of reconnection rate w.r.t.current sheet length Experimental and numerical studies of driven vs spontaneous reconnection, multiple modes (MST) Nonlinear evolution of Parker instability (UNH) Effects of boundary on driven reconnection rate (MRX) Energy release in a line tied medium forced at boundary (UW)

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Theoretical studies on effects beyond MHD Analytical and numerical models of Hall physics (PPPL, UW, UNH) Theory for anomalous resistivity (UC, PPPL) Measurements and kinetic theory of LHDW (PPPL) Simulation of e + e - reconnection (UNH)

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Current sheets in line tied fields Solar, stellar, and accretion disc flares are powered by magnetic fields. Magnetic energy is tapped through resistive dissipation, but resistivity is very low. 2-stage release process: formation of intense current sheets followed by resistive decay. Reduced MHD treatment of a periodic plasma exist for singular kinked equilibria, but not for line tied plasma Simulated in astrophysically relevant line tied plasmas for unrealistically large resistivity.

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Current sheet in bounded plasma has been theoretically studied

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Transition from periodic to line tied condition The mode eigenfunction slowly approaches the periodic case with increasing tube length

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Progress in CMSO Reconnection Research Experimental Progress Identified possible causes of fast reconnection –Hall effects observed through a quadrupole field account for thr high resistivity observed in the low collisionality regime. –Magnetic LHDW fluctuations correlate well with resistivity enhancement Commonality with space observations seen => Collaboration with space physics community An experimental scaling obtained in the transition from collisional to collisionless regime Anomalous ion heating documented Global boundary effects on reconnection studied –by systematic change of boundary –in form of multiple reconnection process

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Progress in CMSO Reconnection Research (II) Theoretical progress Progress made for global reconnection theory –The study of line tying effects has been initiated –Theory of multiple site reconnection is being formulated –Scaling reconnection rate in 2-fluid theory being considered Analytical & numerical theory of local reconnection with anomalous resistivity developed Analytical theory for quadrupole field generation developed Analytical theory of lower hybrid drift instability carried out for the neutral sheet

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Future plans for CMSO reconnection research Causal relationship between the observed Hall effects and magnetic fluctuations with fast reconnection will be studied –3-D consideration Scaling laws for reconnection rateScaling laws for reconnection rate Develop theory of line tied systemsDevelop theory of line tied systems Guiding principles are sought for 3-D global reconnection phenomena –Solar & space physics –Helicity conservation –Global energy flows –Magnetic stochasticity Particle acceleration and heating

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