Magnetic Reconnection: Progress and Status of Lab Experiments In collaboration with members of MRX group and NSF-DoE Center of Magnetic Self-organization Masaaki Yamada SLAC, April 28 th 2011

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 reconnectionAfter reconnection

Solar flare Magnetospheric Aurora-substorm Tokamak Sawtooth disruption Stellar flare time(hour) Magnetic Field strength time(sec) X-ray intensity X-ray intensity Electron temperature Reconnection always occurs very fast (  reconn <<  SP ) after build-up phase of flux

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 B is resistively annihilated in the sheet Mass conservation: Pressure balance: V out V in  reconn <<  SP ~ ６ − ９ months S=Lundquist number

Dedicated Laboratory Experiments on Reconnection DeviceWhereWhenWhoGeometryIssues 3D-CSRussia1970Syrovatskii, FrankLinear3D, heating LPD, LAPDUCLA1980Stenzel, GekelmanLinearHeating, waves TS-3/4Tokyo1990Katsurai, OnoMergingRate, heating MRXPrinceton1995Yamada, JiToroidal, merging Rate, heating, scaling SSXSwarthmore1996BrownMergingHeating VTFMIT1998Fasoli, EgedalToroidal with guide B Trigger RSXLos Alamos2002IntratorLinearBoundary RWXWisconsin2002ForestLinearBoundary

MRX: Dedicated reconnection experiment Goal: Provide fundamental data on reconnection, by creating proto-typical reconnection phenomena, in a controlled setting 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 Local physics problems addressed in collaboration with numerical simulations

I PF Pull Reconnection in MRX

I PF

Experimental Setup and Formation of Current Sheet Experimentally measured flux evolution n e = 1-10 x10 13 cm -3, T e ~5-15 eV, B~ G,

Resistivity increases as collisionality is reduced in MRX 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 Out of plane magnetic field is generated during reconnection P. L. Pritchett, J.G.R 2001 Sheath width ~ c/  pi ~  i

Ion diffusion region The Hall Effect Facilitates Fast Reconnection V in V out ~ V A Electron diffusion region Ideal MHD region Hall term Electron inertia term Electron pressure term The width of the ion diffusion region is c/  pi The width of the electron diffusion region is c/  pe ? Normalized with -j in

MRX with fine 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 Linear probe arrays

Evolution of magnetic field lines during reconnection in MRX Measured region Electrons pull field lines as they flow in the neutral sheet e

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 Collisionless regime : mfp >  Fast reconnection Q-P field present X-type shape

Two-scale Diffusion Region measured in MRX Ion Diffusion region measured:  i > c/  pi Electron Diffusion region newly identified: 6-8 c/  pe <  e Electron jetting measured in both z and y direction : v e > 3-6 V Ai Y. Ren et al, PRL 2008 Presence of B fluctuations

First Detection of Electron Diffusion Layer Made in MRX: Comparison with 2D PIC Simulations All ion-scale features reproduced; but electron-layer is 5 times thicker in MRX Þ importance of 3D effects MRX:  e = 8 c/  pe 2D PIC Sim:  e = 1.6 c/  pe

Measured electron diffusion layer is much broader than 2-D simulation results (Ji, et. al. Sub. GRL 2008) => MMS program

23 Recent (2D) Simulations Find New Large S Phenomena Daughton et al. (2009): PICBhattacharjee et al. (2009):MHD Sweet-Parker layers break up to form plasmoids when S > ~10 4 Impulsive fast reconnection with multiple X points

In a large high S (>10 4 ) system, flux ropes can be generated Daughton et al, Nature Phys.2011 => Impulsive fast reconnection

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

Mozer et al., PRL 2002 POLAR satellite Magnetic Reconnection in the Magnetosphere A reconnection layer has been documented in the magnetopause  ~ c/  pi

Similar Observations in Magnetopause and Lab Plasma ES EM (Space:Bale et al. ‘04) high  low  high  low  (a) (b) (c) EM waves correlate with  MRX EM waves ES waves

MRX scaling shows a transition from the MHD to 2 fluid regime based on (c/  pi )/  sp MRX Scaling:  * vs (c/  i )/  sp Breslau (c/  pi )/  sp ~ 5( mfp /L) 1/2 A linkage between space and lab on reconnection 2 Fluid simulation Nomalized by  Spitz Yamada et al, PoP, 2006

System L (cm)B (G) d i = c/  pi (cm)  sp (cm)d i /  sp MRX RFP/Tokamak 30/ / Magnetosphere Solar flare ISM Proto-star d i /  s >> 1 Linkages between space and lab on reconnection d i /  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: V rec vs. f Impulsiveness

Sawtooth relaxation; reconnection in a tokamak H. Park et al (PRL-06) on Textor 2-D T e 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 T i (eV) E mag (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

Physics Frontier Center for Magnetic Self-organization in Laboratory and Astrophysical plasmas [Sept.03-] U. Wisconsin[PI], U. Chicago, Princeton U., SAIC, and Swarthmore Global Plasma in Equilibrium State Unstable Plasma State Self-organization Processes - Magnetic reconnection -Dynamos -Magnetic chaos & waves -Angular momentum transport Energy Source Reconnection research will build a new bridge between lab and astrophysical scientists

Assume N p =S/Sc D Reconnection “Phase Diagram” for MRX-U Study Collisionless Collisional MHD (Sweet-Parker) Collisional MHD with Plasmoids Hybrid

Petschek model Shock