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

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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