Magnetic Reconnection: Progress and Status of Lab Experiments Masaaki Yamada SLAC, April 28th 2011 In collaboration with members of MRX group and NSF-DoE Center of Magnetic Self-organization Outline • Basic physics issues on magnetic reconnection – Reconnection rate is faster than the classical MHD rate – Fast reconnection <=> Resistivity enhancement – But lower collisionality induces faster reconnection • Two-fluid physics analysis in a local reconnection layer – X-shaped neutral sheet – Physics of Hall effects and experimental verification – Identification of e-diffusion region – Observation of fluctuations (EM-LHDW) • A scaling in transition from MHD to 2-fluid regime • Global reconnection issues; – Reconnection in fusion plasmas – High energy particles – Impulsive reconnection M. Yamada, R. Kulsrud, H.Ji, Rev. Mod. Phys. v.82, 603 (2010) E. Zweibel & M. Yamada, Ann. Rev.AA, AA47-8, 291 (2009) Magnetic Reconnection • Topological rearrangement of magnetic field lines • Magnetic energy => Kinetic energy • Key to stellar flares, coronal heating, particle acceleration, star formation, self-organization of fusion plasmas Before reconnection After reconnection Reconnection always occurs very fast (reconn << SP) after build-up phase of flux X-ray intensity Solar flare time(hour) Magnetospheric Aurora-substorm Magnetic Field strength time(hour) Stellar flare Tokamak Sawtooth disruption X-ray intensity Electron temperature time(sec) Magnetic Reconnection in the Sun • Flux freezing (Ideal MHD) makes storage (flux build up) of magnetic energy easy at the photo surface • Magnetic reconnection occurs when flux freezing breaks • Magnetic reconnection causes conversion of magnetic energy =>radiation, particle acceleration, the kinetic energy of the solar wind. A. Local Reconnection Physics 1. MHD analysis 2. Two-fluid analysis The Sweet-Parker 2-D Model for Magnetic Reconnection Assumptions: • 2D • Steady-state • Incompressibility • Classical Spitzer resistivity Vin Vout B is resistively annihilated B t (v B) 0 in the sheet B 2 V in B Spitz B 0 V in L V out Mass conservation: Pressure balance: reconn << SP ~ 6−9 months 1 2 V out 2 B VA S 2 20 V in V out V A 1 S 0 LV A Spitz S=Lundquist number Dedicated Laboratory Experiments on Reconnection Device Where When Who Geometry Issues 3D-CS Russia 1970 Syrovatskii, Frank Linear 3D, heating LPD, LAPD UCLA 1980 Stenzel, Gekelman Linear Heating, waves TS-3/4 Tokyo 1990 Katsurai, Ono Merging Rate, heating MRX Princeton 1995 Yamada, Ji Toroidal, merging Rate, heating, scaling SSX Swarthmore 1996 Brown Merging Heating VTF MIT 1998 Fasoli, Egedal Toroidal Trigger with guide B RSX Los Alamos 2002 Intrator Linear Boundary RWX Wisconsin 2002 Forest Linear Boundary MRX: Dedicated reconnection experiment Goal: Provide fundamental data on reconnection, by creating proto-typical reconnection phenomena, in a controlled setting Local physics problems addressed in collaboration with numerical simulations The primary issues; • Study non-MHD effects in the reconnection layer; [two-fluid physics, turbulence] • How magnetic energy is converted to plasma flows and thermal energy, • How local reconnection determine global phenomena - Effects of external forcing and boundary Pull Reconnection in MRX IPF Pull Reconnection in MRX IPF IPF Experimental Setup and Formation of Current Sheet Experimentally measured flux evolution ne= 1-10 x1013 cm-3, Te~5-15 eV, B~100-500 G, Resistivity increases as collisionality is reduced in MRX * E j Effective resistivity But the cause of enhanced was unknown Local Reconnection Physics 1. MHD analysis 2. Two-fluid analysis Extensive simulation work on two-fluid physics carried out in past 10 years Sheath width ~ c/wpi ~ i P. L. Pritchett, J.G.R 2001 Out of plane magnetic field is generated during reconnection The Hall Effect Facilitates Fast Reconnection Normalized with E rec V in B rec 0 Hall term Electron inertia term Electron pressure term Ideal MHD region Vin -jin Vout~ VA Ion diffusion region Electron diffusion region • The width of the ion diffusion region is c/wpi • The width of the electron diffusion region is c/wpe ? MRX with fine probe arrays Linear probe arrays • Five fine structure probe arrays with resolution up to ∆x= 2.5 mm in radial direction are placed with separation of ∆z= 2-3 cm Evolution of magnetic field lines during reconnection in MRX e Measured region Electrons pull field lines as they flow in the neutral sheet Neutral sheet Shape in MRX Changes from “Rectangular S-P” type to “Double edge X” shape as collisionality is reduced Rectangular shape Collisional regime: mfp < Slow reconnection No Q-P field X-type shape Collisionless regime: mfp > Fast reconnection Q-P field present Two-scale Diffusion Region measured in MRX Ion Diffusion region measured: i > c/wpi Electron Diffusion region newly identified: 6-8 c/wpe < e Electron jetting measured in both z and y direction : ve > 3-6 VAi Presence of B fluctuations Y. Ren et al, PRL 2008 First Detection of Electron Diffusion Layer Made in MRX: Comparison with 2D PIC Simulations MRX: e = 8 c/wpe 2D PIC Sim: e = 1.6 c/wpe All ion-scale features reproduced; but electron-layer is 5 times thicker in MRX Þ importance of 3D effects Measured electron diffusion layer is much broader than 2-D simulation results => MMS program (Ji, et. al. Sub. GRL 2008) Recent (2D) Simulations Find New Large S Phenomena Bhattacharjee et al. (2009):MHD Daughton et al. (2009): PIC Sweet-Parker layers break up to form plasmoids when S > ~104 Impulsive fast reconnection with multiple X points 23 In a large high S (>104) system, flux ropes can be generated => Impulsive fast reconnection Daughton et al, Nature Phys.2011 Fast Reconnection <=> Two-fluid Physics • Hall MHD Effects create a large E field (no dissipation) • Electrostatic Turbulence • Electromagnetic Fluctuations (EM-LHW) • All Observed in space and laboratory plasmas Magnetic Reconnection in the Magnetosphere A reconnection layer has been documented in the magnetopause ~ c/wpi Mozer et al., PRL 2002 POLAR satellite Similar Observations in Magnetopause and Lab Plasma MRX (a) (Space:Bale et al. ‘04) (b) EM waves EM ES (c) ES waves low low high low high EM waves correlate with MRX Scaling: * vs (c/wi)/ sp Nomalized by Spitz A linkage between space and lab on reconnection Breslau2 Fluid simulation * E j (c/wpi)/ sp ~ 5( mfp/L)1/2 Yamada et al, PoP, 2006 MRX scaling shows a transition from the MHD to 2 fluid regime based on (c/wpi)/ sp Linkages between space and lab on reconnection System L (cm) B (G) di= c/wpi(cm) sp (cm) di/ sp MRX 10 100-500 1-5 0.1-5 .2-100 RFP/Tokamak 30/100 103/ 104 10 0.1 100 Magnetosphere 109 10-3 107 104 1000 Solar flare 109 104 102 100 107 1010 0.001 ISM Proto-star 1018 100 10-6 di/ s >> 1 di/ sp ~ 5( mfp/L)1/2 Global study of magnetic reconnection How is reconnection rate determined by global boundary conditions? 1. Flux build up phase 2. Magnetic self-organization External forcing: Vrec vs. f Impulsiveness Sawtooth relaxation; reconnection in a tokamak H. Park et al (PRL-06) on Textor 2-D Te profiles obtained by measuring ECE (electron cyclotron emission) represent magnetic fluxes Sawtooth crash (reconnection) occurs after a long flux build up phase H ~ 200 msec re ~ 0.2 msec reconn << SP Generation of high energy electron during reconnection Suvrukhin, 2002 Ion Temperature increases during RFP sawtooth reconnection Ti (eV) Emag (kJ) Summary • Progress has been made in reconnection research both in laboratory and space astrophysical observations => collaboration started in study of magnetic reconnection/self-organization – Transition from collisional to collisionless regime documented – A scaling found on reconnection rate • Notable progress made for identifying causes of fast reconnection – Two fluid MHD physics plays dominant role in the collisionless regime. Hall effects have been verified through a quadrupole field – Electron diffusion identified – Impulsive reconnection coincides with disruption of formed current sheet – Causal relationship between these processes for fast reconnection is yet to be determined • Guiding principles to be found for 3-D global reconnection phenomena – Magnetic self-organization – Global forcing – Impulsive reconnection after flux build-up • Reconnection research will build a new bridge between lab and astrophysical scientists Global Plasma in Equilibrium State Self-organization Processes Energy Source -Magnetic reconnection -Dynamos -Magnetic chaos & waves -Angular momentum transport Unstable Plasma State Physics Frontier Center for Magnetic Self-organization in Laboratory and Astrophysical plasmas [Sept.03-] U. Wisconsin[PI], U. Chicago, Princeton U., SAIC, and Swarthmore 2D Reconnection “Phase Diagram” for MRX-U Study 14 12 S 10 2 Sc Assume Np=S/Sc Hybrid Collisionless 8 6 S MHD Collisional with Plasmoids 4 S c 10 2 Collisional MHD (Sweet-Parker) 2 4 log( ) 6 8 L /S 10 3 4 Petschek model Shock V Re c 1 ln S V A