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 Slide 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 Slide 3 3 Magnetic
Reconnection Before reconnection Slide 4 4 Field lines break and
reconnect Magnetic Reconnection Slide 5 5 After reconnection
Magnetic Reconnection Slide 6 6 Topological rearrangement of
magnetic field lines Magnetic energy => Kinetic energy Before
reconnectionAfter reconnection Magnetic Reconnection Slide 7 X-rays
7 Solar Flares Magnetic reconnection H Based on K. Shibata (2007)
Slide 8 Slide 9 Solar Wind Interacts With Earths Magnetosphere 9
Slide 10 -Ray Flares from Crab Nebula (Fermi) Striani et al. (2011)
Slide 11 11 1-D Diffusion of Magnetic Field Is Very Slow ~10 6
years for solar flares of minutes to hours Slide 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
Slide 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? Slide 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 Slide 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 Slide 16 16 Magnetic
Reconnection Experiment (MRX) (since 1995, mrx.pppl.gov) Slide 17
17 Experimental Setup in MRX Controllability and diagnostics are
key Slide 18 18 Realization of Stable Current Sheet and
Quasi-steady Reconnection Detailed diagnostics: quantitative
studies possible Slide 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 Slide 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) Slide 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 Slide 22 22 B 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) Slide 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 Slide 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 Slide 25 25
Larger size Stronger field More power More controls MRX-U Is
Proposed to Access New Phases Engineering Design Underway Slide 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 Slide 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 Slide 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 Slide 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 Slide 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.