1. Laboratory Studies of Magnetic Reconnection – Status and Opportunities – HEDLA 2012 Tallahassee, Florida April 30, 2012 Hantao Ji Center for Magnetic Self-organization in Laboratory and Astrophysical Plasmas Princeton Plasma Physics Laboratory, Princeton University

2. 2 Outline Magnetic reconnection as a major dissipation mechanism Some basic ideas about magnetic reconnection Magnetic Reconnection Experiment (MRX) –Testing Sweet-Parker model (MHD scale) –Verification of Hall effects for fast reconnection (ion scale) –Identification of electron diffusion region (electron scale in 2D) –Flux rope dynamics and impulsive reconnection (electron scale in 3D) Opportunities –MRX-Upgrade to access more astrophysically relevant “reconnection phases” –HED experiments to reach unique, extreme parameters

3. 3 Magnetic Reconnection Before reconnection

4. 4 Field lines break and reconnect Magnetic Reconnection

5. 5 After reconnection Magnetic Reconnection

6. 6 Topological rearrangement of magnetic field lines Magnetic energy => Kinetic energy Before reconnectionAfter reconnection Magnetic Reconnection

7. X-rays 7 Solar Flares Magnetic reconnection Hα Based on K. Shibata (2007)

9. Solar Wind Interacts With Earth’s Magnetosphere 9

10. ϒ -Ray Flares from Crab Nebula (Fermi) Striani et al. (2011)

11. 11 1-D Diffusion of Magnetic Field Is Very Slow ~10 6 years for solar flares of minutes to hours

12. 12 2-D Diffusion of Magnetic Field: Magnetic Reconnection In 2-D, magnetic field lines can diffuse much faster around an X-line because newly reconnected field lines move out of the diffusion region quickly due to a tension force, converting magnetic energy to flow energy

13. 13 Classical 2D Reconnection Model in MHD: Sweet-Parker Model vs Petschek Model Lundquist #: …but not a steady state solution with uniform resistivity …but still much longer than the observations of a few minutes What do we see in the lab?

14. 14 Two Types of Experiments All-in-one: many competing processes coexist; difficult to differentiate –e.g. tokamaks Problem-specific: one process dominates –e.g. MRX for magnetic reconnection Controllability is the key: specify conditions, when, and where to observe how; diagnostics is the other key

15. 15 Dedicated Laboratory Experiments on Reconnection DeviceLocationStartInvestigatorsGeometryIssues 3D-CSRussia1970Syrovatskii, FrankLinear3D, heating LPD, LAPDUCLA1980Stenzel, GekelmanLinearHeating, waves TS-3/4Tokyo1990Ono, InomotoMergingRate, heating MRXPrinceton1995Yamada, JiToroidal, merging Rate, heating, scaling, 3D SSXSwarthmore1996Brown, GreyMergingHeating, 3D VTFMIT1998EgedalToroidal with guide B Trigger, 3D RSXLos Alamos2002IntratorLinearBoundary, 3D RWXWisconsin2002ForestLinearBoundary

16. 16 Magnetic Reconnection Experiment (MRX) (since 1995, mrx.pppl.gov)

17. 17 Experimental Setup in MRX Controllability and diagnostics are key

18. 18 Realization of Stable Current Sheet and Quasi-steady Reconnection Detailed diagnostics: quantitative studies possible

19. 19 Classical S-P model predicts reconnection rate at First quantitative tests were done in the lab (MRX); correct only with modifications: Importance of effective resistivity enhancement and boundaries model Ji et al. PRL (1998) PoP (1999) Quantitative Agreement with a Generalized Sweet-Parker Model

20. 20 Two-fluid Effects Are Essential for Fast Reconnection Numerical prediction of quadrupole out-of-plane field Definite confirmation by 2D measurements in the lab (MRX, SSX), with theoretically expected dependence on the collisionality Consistent with 1D space data Ren et al. PRL (2005) Yamada et al. PoP (2006) Matthaeus et al. GRL (2005), Brown et al. POP (2006) (e.g. Drake et al. ‘98) Mozer et al. PRL (2002)

21. 21 The Next Frontier: Electron Diffusion Region (cf. the MMS mission) All ion-scale features reproduced by 2D PIC simulations, but e-layer is thicker in MRX; 3D physics important? Ren et al. PRL (2008) Ji et al. GRL (2008) Dorfman et al. PoP (2008) Royteshteyn et al. POP (2010) MRX:  e = 8 c/  pe 2D PIC Sim:  e = 1.6 c/  pe

22. 22 δB z (Gauss) 2-4.5MHz Gray= No Measurement Fluctuations peak near the disruption time Flux Rope Ejection Impulsive Reconnection due to 3D Flux Rope Ejection from Current Sheet Dorfman et al. submitted to PRL (2012)

23. What Are Future Major Opportunities for Reconnection Experiments? 23 1.MRX-upgrade to access new “reconnection phases” for direct astrophysical relevance 2.HED experiments to access unique extreme conditions

24. 24 Ji & Daughton (2011) New Reconnection Phases Provide Accesses to Astrophysical Reconnection Multiple X-line reconnection may also provide a solution of efficient particle accelerations

25. 25  Larger size  Stronger field  More power  More controls MRX-U Is Proposed to Access New Phases Engineering Design Underway

26. What Are Future Major Opportunities for Reconnection Experiments? 26 1.MRX-upgrade to access new “reconnection phases” for direct astrophysical relevance 2.HED experiments to access unique extreme conditions

27. Magnetic Reconnection is Considered to be also Important in Flow-Dominated Regimes Sunspots are magnetic, drifting towards equator, and then disappear. What happens to these sunspots? 27 Flock et al. (2011) Reconnection dominates dissipation in low-beta regions of accretion disks

28. A New Venue Is Emerging to Study Reconnection under Flow-Driven Conditions 28 Ion diffusion region with the width of ~d i Electron diffusion region with the width of ~10d e Nilson et al. (2006) Zhong et al. (2010) Bi-directional plasma jets observed

29. Outstanding Questions for HED Reconnection Experiments How to distinguish reconnection from other effects, such as shocks? What are magnetic and plasma structures of reconnection region? What are ion and electron angle distributions and energy spectra? What are effects due to system size and plasma beta? What are effects due to relativity, radiation, strong magnetization? 29 H. Ji, E. Blackman, C. Ren, P. Nilson, et al. (2011) Anti-parallel reconnection Component reconnection No reconnection Controllability and diagnostics are key

30. 30 Summary Magnetic reconnection is an important dissipation process in nearly all laboratory, space and astrophysical plasmas. Rich, multi-scale physics is being studied in magnetically driven systems –Sweet-Parker model tested quantitatively (MHD scale) –Hall effects verified for fast reconnection (ion scale) –Electron diffusion region identified and being studied (electron scale in 2D) –3D flux rope dynamics lead to current disruption and impulsive reconnection (electron scale in 3D) MRX-Upgrade is being proposed to study new reconnection phases, and their scaling towards direct space and astrophysical applications including particle acceleration. New opportunities emerging for HED experiments to study reconnection in flow-driven systems. Controllability and diagnostics are key for success.