Progress and Planson Magnetic Reconnection for CMSO

M. Yamada, C. Hegna, E. Zweibel

For General meeting for CMSOAugust 4, 2004

1. Recent progress and plansExperiment-YamadaTheory-Hegna, Malshkin, Lazarian

2. Discussions on Plans

Experimental Progress and Plans Outline

-Recent progress by CMSO research and its relationship to space physics

• Understanding of local reconnection physics advanced- 2 Fluids MHD- Hall MHD physics- EM Fluctuations: Whistler waves- Current sheet profiles

• Global reconnection physics being developed- Plasma merging

• Plans- 2 Fluids MHD physics study will continue- Role of reconnection in dynamos and ion heating

Four devices [MRX, MST, SSX, and SSPX] are available for reconnection research in CMSO

MRX

SSX

MST

SSPX

Global reconnection sequence in solar flare

• Observation by Yokoyama et al, Vrecc/VA ~ 0.002- 0.011

Current Physics Issues on Magnetic Reconnection

1. Local vs global physics– Global boundary conditions influence or determine

local reconnection dynamics or forced reconnection– Local sheet physics influences global topology

evolution and relaxation rate

2. Collisional vs collisionless reconnection– Classical collisions and non-classical collisions

(fluctuations)– Hall term effects

Global Reconnection Physics Results from Recent Laboratory Experiments

• Plasma Merging– Counter-helicity merging rate >> Co-helicity merging rate

[TS-3, SSX, MRX] • Magnetic helicity conservation

– Helicity conservation studied [TS-3]– Flux inventory during reconnection [MST, SSPX]

• Identification of Hall dynamos in MST => Dynamo session

• There are very few quantitative data from space to verify the above results, but there are many interesting implications

Local issue; Two competing models to

explain fast reconnection

• 1-Fluid MHD model + effective resistivity (Effects of waves)

•2-Fluids MHD; decoupling of ions and electrons within the ion skin depth, cpi; -> Including the Hall term, jexB

Dedicated lab experiments [LLPD(EMHD), MRX, SSX, TS-3, VTF etc.]

Generalized Sweet-Parker model Petschek-type Model

2-D numerical simulation can assess 2-fluids effects

Je

Ji

Vi

Jpne

1BJ

nec

1Bv

c

1E

dt

Jd4ei2

pe

Below c/pi electron and ion motion decouple•electrons frozen-in to B

•Observed out-of-plane quadrupole fields•Obtained a thin electron current layer of c/pe

Drake et al

These results have not been verifiedin lab experiments

A force valance observed in the MRX shows a strong effect of Hall term

• A force balance in incoming (x) direction would give;

Jy x Bz = px

or [p + Bz2]/20 ~ const.

Generalized Ohm’s law: Jpne1

BJnec1

Bvc1

EdtJd4

ei2pe

Phys. Plasmas, v. 7, 1781 (2000)

Contour; E + v B

=210-3; =10-2; c/pi=2.27710-2

2 Fluid TheoryBreslau et al., 2004

E + vxB ~ 0

E = const.

Steady state dB/dt =Curl E

c/pi

Hall term should play a major role in force balance

=210-3; =10-2; c/pi=2.27710-2

E + v B (j B)/neej= +

Fluid Flow Lines

=210-3; =10-2; c/pi=2.27710-2

flux contours

separatrix

ion flow

electron flow

symmetry axes

Max ion speed is 1.084 vA at (.464, 0) and (.735, 0).

Max electron speed is 3.302 vA at (.562, 0) and (.631, 0).

c/pi

2D Current Profile with Hall Term and Elevated Resistivity

=10-2;=10-2; c/pi=2.27710-2

Major Goals for Magnetic Reconnection in CMSO

• 1) Study 2-fluid MHD effects through the generalized Ohm’s law in the reconnection region and determine the role of turbulence in reconnection process.

• 2) Find key relationships between the local physics of the reconnection layer and the dynamics of global plasma reconnection phenomena.

• 3) Identify key 3-D effects on reconnection, whether intrinsic or due to boundary conditions.

• 4) Evaluate the role of magnetic reconnection in dynamos, ion heating, and, more generally, in other magnetic self-organization phenomena.

The measured current sheet profiles agree well

with Harris theory

(MRX dataPhys. Plasmas, 7, 1781, 2000)

Sheet width agrees with Harris model demonstrating 2-fluid MHD effects

• scales with c/pi

~ constant vd/vthe

• is not determined by Sweet-Parker thickness

Reconnection speeds up drastically in low collisionality regime

What causes the anomalous resistivity?M

easu

red

resi

stiv

ity

Trintchouk et al, PoP 2003

Collisionality

Reconnection rate is enhanced for (c/pi)/sp >1

Breslau et al,

)10( 314* cmns

ei

V

VV

17103 810 1410

810 610

810 510 1310

2/1

*

*4/3

*

*

2/1ln

57.6

L

B

n

T

V

VV

s

ei

spH

ei

iie

piH VV

mTTc

2

S

Lsp S

System L* (10cm) B* (100G) T* (10ev)

MRX 1 1 1 1 2.04

Astrophysics 0.1 0.0014

Solar Flares 1 10 26.53

Magnetosphere 1 2320

Tokamak 10 100 1 1000 893.6

, which comes from , where , and is the

Lundguist number.

If Ratio of the Sweet-Parker thickness to the Ion Inertia Length, = 1

Measurements of Diffusion Regionwith a Hall effect signature

Mozer et al., PRL 2002

POLAR satellite

A reconnection layer has been documented in the magnetopause

Fast Reconnection <=> Enhanced Resistivity

• Main question

– What is the cause of the observed enhanced

resistivity?

• Electrostatic Turbulence

• Electromagnetic Fluctuations

• 2 Fluids effects

» All effects may be coupled in MRX

Turbulence Amplitudes Correlate with Resistivity Enhancement

MRX has been upgraded to address major reconnection physics issues in collision-less regime

Lager S number expected with higher B and Te

New fine structure probe

71 channels

Vacuum vessel extended

Initial measurement of fine structure of the neutral sheet

Confirms the previously seen Harris current sheet profile.

As the current sheet thins, deviations from the Harris tanh profile are seen in a transient phase.

Magnetic reconnection in MST Two fluid effects can significantly alter the

reconnection and dynamo, for < c/pi

j ˜ v ˜ B ˜ j ˜ B

neMHD term Hall term

S. Prager’s talk

Hall dynamo large near resonant surface

PRL July 23, 2004

SSX- Merging Experiments

/

Mode I

Mode II

Generalized Ohm’s Law has been addressed in SSX

• JxB term is evaluated to be much larger than collisional resistivity term and inertia term

[Cothran et al. to be submitted to GRL]=> M. Brown’s talk

Magnetic structure consistent with FRC/doublet-CT

SSX (Swarthmore) 2002

•Reversed field•Very little midplane toroidal field•Axially antisymmetric B•70 G RCC field (on axis)

Summary

Progress being made in laboratory experiments

• Transition from Sweet-Parker (collisional) to 2-fluid MHD regime documented ; A new scaling found

• Hall effects have been experimentally studied in the neutral sheets [MRX, SSX] as well as in the unstable flux surfaces [MST]

• Magnetic turbulence [whistler waves] identified in the neutral sheet, correlates well with resistivity enhancement

• With regard to the fine properties of the neutral sheet, a close interrelationship to space observations (in the magnetosphere) has been established; WIND, GEOTAIL, Cluster

• Conclusive guiding principles may be yet to be found in reconnection with global reconnection– Magnetic helicity, 2 fluids effects

Short-Intermediate Term Research Objectives

• 1) Investigate local dynamics in the vicinity of the neutral sheet to assess 2-fluid MHD processes, such as Hall and turbulence effects.

• 2) Explore the relationship between anomalous ion heating and reconnection events in both laboratory and astrophysical plasmas, and investigate why Ti is

generally higher than Te in reconnection region.

• 3) Investigate how the local reconnection process is related to global reconnection and dynamo activity.

• 4) Role of reconnection in dynamos

Local Reconnection Physics Results from Recent Laboratory Experiments

• Current sheet profiles ~ c/pi, consistent with theory; MRX, SSX, TS-3, GEOTAIL, WINDS

– B tanh(x/), in MRX, VTF, agrees with space data [ Mozer et al.]

• Reconnection rate– Consistent with a generalized Sweet-Parker Model [MRX]

• Plasma resistivity– Verification of Spitzer perpendicular resistivity in collisional limit

[MRX]

– Enhanced in less collisional [MRX, TS-3] and collisionless [VTF] cases

• Fluctuations– Detected by electrostatic and magnetic probes [MRX, VTF]

– Magnetic fluctuations around Lower Hybrid frequency correlate well with the resistivity enhancement [MRX] <=> WIND, GEOTAIL, Cluster