Results from Magnetic Reconnection ExperimentAnd Possible Application to Solar B program
For Solar B Science meeting,Kyoto, Japan
November 8-11, 2005
Masaaki YamadaPrinceton University, PPPL
In collaboration with Y. Ren, H. Ji, S. Gerhardt, R. Kuslrud, and A. Kuritsyn
Solar flare
MagnetosphericAurora-substorm
Laboratoryreconnection
Tokamak disruption
Protostellarflare
time(hour)
time(hour)
MagneticField
strength
time(μsec)
time(sec)
time 105 sec
X-rayintensity
X-rayintensity
MagneticField
strength
Electrontemperature
Various “Flares” (Reconnection Phenomena)
Physics Frontier Center for Magnetic Self-organization in Laboratory and Astrophysical plasmas [9/15/03-]
U. Wisconsin[PI], U. Chicago, Princeton U., SAIC, and Swarthmore
Global Plasma in Equilibrium State
Unstable PlasmaState
Self-organization Processes Dynamo Magnetic reconnection Magnetic chaos & waves Angular momentum transport Ion Heating Magnetic helicity conservation
External Energy Source
• New bridges, collaborations between lab and astrophysical scientists
Outline• Introduction: Magnetic Reconnection in Lab Plasmas
– Examples
• MHD (magneto-hydrodynamic) analysis– Sweet-Parker model and its generalization– Fast reconnection <=> Resistivity enhancement
• Two-fluid MHD physics regimes– High frequency turbulence– Generalized ohm’s law
• Experimental study of Hall effects;– Verification of an out-of-plane quadrupole field
• A new scaling identified from MHD to 2-fluid regime• Summary [Interim report]• Opportunities for collaborative study
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
reconn << SP
Local view of reconnection in a tokamak
QuickTime™ and aVideo decompressor
are needed to see this picture.
From H. Park
MRX upgraded in FY2004• Relocated the PF and TF power supplies, increased stored energy (500 kJ)• Extended vacuum vessel to allow greater flux-core separation
Several dedicated experiments address the physics of magnetic reconnection
TS-3/SSX
process steady state transient
boundarylocal global
collisionalitycollisionless collisional
3-D
2-D
Objectives of MRX [Magnetic Reconnection Experiment]MRX was built to provide fundamental data on magnetic reconnection, by creating a proto-typical reconnection layer,
in a controlled laboratory setting. The primary issues;
• How much the theoretical 2-D reconnection picture is valid in actual experiments,
• How does guide field affect reconnection rate• What kinds of non-MHD effects would dominate in the
reconnection layer,
• How the magnetic energy is converted to plasma flows and thermal energy,
• What is a guiding principles for global reconnectionGlobal 2-D and 3-D MHD effects on reconnection,
Experimental Setup and Formation of Current Sheet
Experimentally measured flux plots
ne= 1-10 x1013 cm-3, Te~5-15 eV, B~100-500 G,
Flux core distance can be changed
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
The measured current sheet profiles agree well
with Harris theory
(Yamada et al.,→ . , Phys Plasmas7, 1781, 2000)
Resistivity Enhancement Depends on Collisionality
η* ≡EθjθEθ +VR ×BZ =ηjθ
Agreement with a Generalized Sweet-Parker Model
• The model modified to take into account of– Measured enhanced
resistivity
– Compressibility
– Higher pressure in downstream than upstream
(Ji et al. PoP ‘99)
GSP
model
Fast Reconnection <=> Enhanced Resistivity
• Main question
– What is the cause of the observed enhanced
resistivity?
• Hall MHD Effects create a large E field
• Electrostatic Turbulence
• Electromagnetic Fluctuations» All Observed in MRX
Two Models for Fast Reconnection
Generalized Sweet-Parker model with anomalous resistivity.
Two-fluid MHD model in which electrons and ions decouple in the diffusion region (~ c/pi).
Vin
Vout» Va
€
E + V × B = ηJ +J × B −∇p
en+
me
e2
dVe
dt
The Hall Effect During Reconnection Shown in 2D Simulation
A out-of-plane quadrupole magnetic field
2-fluid MHD simulation performed by J. Breslau with the 2-D Magnetic Reconnection Code (MRC).
Different motions of ions and electrons
In-plane current
• The blue lines show the ion flow streamlines.
• The red arrows show the electron flow.
• The black lines show the magnetic flux.
The colors show the out-of-plane
quadrupole magnetic field.
The Out-of-plane Magnetic Field is Generated by Differential Electron Flow
The Fine Structure Probe allows measurements within the current sheet with 1.25 mm resolution
5 cm cpi
≈ 2-10 cm.
cpe
≈ .5-2.5 mm.
1.25 mm
Fine Structure Probe [∆ =1mm]
MRX Data
Experimentally measured 3-D field line features in MRX
• Manifestation of Hall effects in MRX• Electrons would pull magnetic field lines with their flow
e flow
Evolution of magnetic flux contours during MRX reconnection
Measurements of Diffusion Regionwith a Hall effect signature
Mozer et al., PRL 2002
POLAR satellite
A reconnection layer has been documented in the magnetopause
~ c/pi
The Electron Flow Velocity is Deduced
• Good agreement between the measurement and the yellow region in the simulation.
Separatrix
Measurement Simulation• A new MRX high resolution
probe array (R =0.25mm) shows electron flow patterns to create a quadrupole field
(preliminary data)
• Comparison of high and low density cases:
• No Q-P field seen in collisional plasmas
Collisional regimemfp <
Collisionlessl regimemfp >
Self-made quadrupole field size versus fill pressure Collisions reduce the Hall effects
Bz is the shoulder value of reconnecting field.
The Hall Term is Dominant in Generating the Reconnection Electric Field
• The ratio between the jrx Bz/ene and the reconnection electric field is evaluated.
• The /mfp denotes the
collisionality of plasmas.
CollisionalCollisionless
The Hall term is important when |/mfp|<1.
EM LHDW Amplitudes Correlate with Resistivity Enhancement
The lower hybrid drift waves [LHDW] are excited by electron drift again ions [Ji et al., PRL-04]
Similar Observation by Spacecraft at Earth’s Magnetopause
(Phan et al. ‘03)
ES
EM
(Bale et al. ‘04)
high
low
high
low
low
System L (cm) B (G)di= c/pi(cm)
sp (cm) di/ sp
MRX/SSX 10 100-500 1-5 0.1-5 .2-100
MST 30/100 1-3x103 10 0.1 100
Magnetosphere 109 10-3 107 104 >103
Solar flare 109 100 104 102 100
ISM 1018 10-6 107 1010 0.001
Protostar di/ s >> 1
MRX scaling shows transition from collisional (MHD) regime to 2 fluid MHD regimew.r.t. normalized ion skin depth
A linkage between space and lab on reconnection
Breslau
di/ sp ~ 5( mfp/L)1/2
Summary
• Important progress has been made both in laboratory experiments and solar and space observations making it possible to collaborate in study of magnetic reconnection/self-orhanization
– Transition from collisional to collisionless regime documented– Generalized Sweet Parker model was tested in an axisymmetric (2-D) plasma
• Progress maid for identifying causes of fast reconnection– Electrostatic and magnetic LHDW fluctuations have been observed; Magnetic
not electrostatic turbulence in the sheet correlates well with resistivity enhancement
– Two fluid MHD physics plays dominant role in the collisionless regime. Hall effects have been verified through a quadrupole field
– Causal relationship between these processes with fast reconnection is yet to be determined
• Guiding principles yet to be found for 3-D global reconnection phenomena in the collisionless regime
– Magnetic self-organization– Global energy flows
Opportunities for Collaborative Research
• Transition scaling can be checkedTransition scaling can be checked in a broader basis in a broader basis
using dusing dii//SPSP in the transition from collisional to collisionless in the transition from collisional to collisionless regimesregimes
• Effects of guide field on magnetic reconnectionEffects of guide field on magnetic reconnection
• Guiding principles can be sought together for 3-D global reconnection phenomena– Magnetic self-organization-Minimum energy state– Multiple reconnection models for global self-organization– Conservation of magnetic helicities– Plasmoid formation
• Mechanisms of effective ion heating both in Lab and coronaeMechanisms of effective ion heating both in Lab and coronae
Global Physics for Helicity
Counter-helicity merging generates
FRC and strong ion heating
TS-3 Data