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Progress and Plans on Magnetic Reconnection for CMSO M. Yamada, C. Hegna, E. Zweibel For General meeting for CMSO August 4, Recent progress and plans Experiment-Yamada Theory-Hegna, Malshkin, Lazarian 2. Discussions on Plans

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Experimental Progress and Plans Outline - Recent progress by CMSO research and its relationship to space physics Understanding of local reconnection physics advanced - 2 Fluids MHD - Hall MHD physics - EM Fluctuations: Whistler waves - Current sheet profiles Global reconnection physics being developed - Plasma merging Plans - 2 Fluids MHD physics study will continue - Role of reconnection in dynamos and ion heating

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Four devices [MRX, MST, SSX, and SSPX] are available for reconnection research in CMSO MRX SSX MST SSPX

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Global reconnection sequence in solar flare Observation by Yokoyama et al, V recc /V A ~

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Current Physics Issues on Magnetic Reconnection 1. Local vs global physics –Global boundary conditions influence or determine local reconnection dynamics or forced reconnection –Local sheet physics influences global topology evolution and relaxation rate 2. Collisional vs collisionless reconnection –Classical collisions and non-classical collisions (fluctuations) –Hall term effects

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Global Reconnection Physics Results from Recent Laboratory Experiments Plasma Merging –Counter-helicity merging rate >> Co-helicity merging rate [TS-3, SSX, MRX] Magnetic helicity conservation –Helicity conservation studied [TS-3] –Flux inventory during reconnection [MST, SSPX] Identification of Hall dynamos in MST => Dynamo session There are very few quantitative data from space to verify the above results, but there are many interesting implications

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Local issue; Two competing models to explain fast reconnection 1-Fluid MHD model + effective resistivity (Effects of waves) 2-Fluids MHD; decoupling of ions and electrons within the ion skin depth, c pi ; -> Including the Hall term, j e xB Dedicated lab experiments [LLPD( EMHD ), MRX, SSX, TS-3, VTF etc.] Generalized Sweet-Parker modelPetschek-type Model

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2-D numerical simulation can assess 2-fluids effects JeJe JiJi ViVi Below c/ pi electron and ion motion decouple electrons frozen-in to B Observed out-of-plane quadrupole fields Obtained a thin electron current layer of c/ pe Drake et al These results have not been verified in lab experiments

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A force valance observed in the MRX shows a strong effect of Hall term A force balance in incoming (x) direction would give; J y x B z = p x or [p + B z 2 ]/2 0 ~ const. Generalized Ohms law: Phys. Plasmas, v. 7, 1781 (2000)

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Contour; E + v B = ; =10 -2 ;c/ pi = Fluid Theory Breslau et al., 2004 E + vxB ~ 0 E = const. Steady state dB/dt =Curl E c/ pi

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Hall term should play a major role in force balance = ; =10 -2 ;c/ pi = E + v B(j B)/n e e j =+

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Fluid Flow Lines = ; =10 -2 ;c/ pi = flux contours separatrix ion flow electron flow symmetry axes Max ion speed is v A at (.464, 0) and (.735, 0). Max electron speed is v A at (.562, 0) and (.631, 0). c/ pi

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2D Current Profile with Hall Term and Elevated Resistivity =10 -2 ; =10 -2 ;c/ pi =

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Major Goals for Magnetic Reconnection in CMSO 1) Study 2-fluid MHD effects through the generalized Ohms law in the reconnection region and determine the role of turbulence in reconnection process. 2) Find key relationships between the local physics of the reconnection layer and the dynamics of global plasma reconnection phenomena. 3) Identify key 3-D effects on reconnection, whether intrinsic or due to boundary conditions. 4) Evaluate the role of magnetic reconnection in dynamos, ion heating, and, more generally, in other magnetic self- organization phenomena.

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The measured current sheet profiles agree well with Harris theory

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Sheet width agrees with Harris model demonstrating 2-fluid MHD effects scales with c/ pi ~ constant v d /v the is not determined by Sweet-Parker thickness

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Reconnection speeds up drastically in low collisionality regime What causes the anomalous resistivity? Measured resistivity Trintchouk et al, PoP 2003 Collisionality

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Reconnection rate is enhanced for (c/ pi )/ sp >1 Breslau et al,

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System L * (10cm)B * (100G)T * (10ev) MRX Astrophysics Solar Flares Magnetosphere12320 Tokamak , which comes from, where, and is the Lundguist number. If Ratio of the Sweet-Parker thickness to the Ion Inertia Length, = 1

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Mozer et al., PRL 2002 POLAR satellite A reconnection layer has been documented in the magnetopause

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Fast Reconnection Enhanced Resistivity Main question –What is the cause of the observed enhanced resistivity? Electrostatic Turbulence Electromagnetic Fluctuations 2 Fluids effects » All effects may be coupled in MRX

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Turbulence Amplitudes Correlate with Resistivity Enhancement

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MRX has been upgraded to address major reconnection physics issues in collision-less regime Lager S number expected with higher B and T e New fine structure probe 71 channels Vacuum vessel extended

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Initial measurement of fine structure of the neutral sheet Confirms the previously seen Harris current sheet profile. As the current sheet thins, deviations from the Harris tanh profile are seen in a transient phase.

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Magnetic reconnection in MST Two fluid effects can significantly alter the reconnection and dynamo, for < c/ pi MHD termHall term S. Pragers talk

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Hall dynamo large near resonant surface PRL July 23, 2004

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SSX- Merging Experiments / Mode I Mode II

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Generalized Ohms Law has been addressed in SSX JxB term is evaluated to be much larger than collisional resistivity term and inertia term [Cothran et al. to be submitted to GRL] => M. Browns talk

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Magnetic structure consistent with FRC/doublet-CT SSX (Swarthmore) 2002 Reversed field Very little midplane toroidal field Axially antisymmetric B 70 G RCC field (on axis)

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Summary Progress being made in laboratory experiments Transition from Sweet-Parker (collisional) to 2-fluid MHD regime documented ; A new scaling found Hall effects have been experimentally studied in the neutral sheets [MRX, SSX] as well as in the unstable flux surfaces [MST] Magnetic turbulence [whistler waves] identified in the neutral sheet, correlates well with resistivity enhancement With regard to the fine properties of the neutral sheet, a close interrelationship to space observations (in the magnetosphere) has been established; WIND, GEOTAIL, Cluster Conclusive guiding principles may be yet to be found in reconnection with global reconnection –Magnetic helicity, 2 fluids effects

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Short-Intermediate Term Research Objectives 1) Investigate local dynamics in the vicinity of the neutral sheet to assess 2-fluid MHD processes, such as Hall and turbulence effects. 2) Explore the relationship between anomalous ion heating and reconnection events in both laboratory and astrophysical plasmas, and investigate why T i is generally higher than T e in reconnection region. 3) Investigate how the local reconnection process is related to global reconnection and dynamo activity. 4) Role of reconnection in dynamos

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Local Reconnection Physics Results from Recent Laboratory Experiments Current sheet profiles – ~ c/ pi, consistent with theory; MRX, SSX, TS-3, GEOTAIL, WINDS –B tanh(x/ ), in MRX, VTF, agrees with space data [ Mozer et al.] Reconnection rate –Consistent with a generalized Sweet-Parker Model [MRX] Plasma resistivity –Verification of Spitzer perpendicular resistivity in collisional limit [MRX] –Enhanced in less collisional [MRX, TS-3] and collisionless [VTF] cases Fluctuations –Detected by electrostatic and magnetic probes [MRX, VTF] –Magnetic fluctuations around Lower Hybrid frequency correlate well with the resistivity enhancement [MRX] WIND, GEOTAIL, Cluster

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