Progress and Plans on Magnetic Reconnection for CMSO

Progress and Planson Magnetic Reconnection for CMSO

For NSF Site-Visit for CMSOMay1-2, 2005

1. Experimental progress [M. Yamada] -Findings on two-fluid physics

2. Theoretical progress [E. Zweibel] -Effects of global boundary conditions

3. Summary and Research Plans

Magnetic Reconnection

• Topological rearrangement of magnetic field lines• Magnetic energy => Kinetic energy• Key to stellar flares, coronal heating, particle acceleration, star formation,

energy loss in lab plasmas* A key question: Why does reconnection generally occur so fast?

Before reconnection After reconnection

Major Goals for Magnetic Reconnection in CMSO

• √ (1) Study 2-fluid effects in the reconnection region and determine the role of fluctuations.

• √ (2) Find key relationships between the local physics of the reconnection layer and the dynamics of global reconnection, including boundary conditions.

• √ (3) Develop universal parameter scalings for reconnection applicable both space and laboratory plasmas

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

Four devices [MRX, MST, SSX, and SSPX] are available for

reconnection research in CMSO

MRX

SSX

MST

SSPX

Experiments are supported by numerical modeling and theory

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 CMSO experiments

Two Models to Fast Magnetic Reconnection

Generalized Sweet-Parker model with anomalous resistivity.

Presence of EM fluctuations

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

Two types of reconnection layer profiles observed in MRX

• High density collisional regime

• Low density collisionless regime

Experimentally measured 3-D field line features in MRX

• Manifestation of Hall effects in MRX: Out-of-plane quadrupole field• Electrons pull magnetic field lines with their flow

The Electron Flow Profile is Measured

• Good agreement between the measurement and the simulation (yellow region).

Measurement Simulation

A MRX high resolution probe array

(R = 2.5 mm) shows electron flow patterns to create an out-of-plane QP field

(EM fluctuation present)

Measurements of Diffusion Regionwith a Hall effect signature

Mozer et al., PRL 2002

POLAR satellite

Striking similarities with the the data from the magnetopause

~ c/pi

EM & ES fluctuation profiles are very similar

MRX scaling shows transition from the MHD (collisional) to 2 fluid regime based on normalized ion skin depth

MRX Scaling:A linkage between space and lab on reconnection

Breslau di/ sp ~ 5( mfp/L)1/2

Quadrupole out-of-plane fieldhas been reported by SSX push reconnection

experiment

Ion inertial scale 2 cm

Hall term is also strong in MST

Determining reconnection rate and E field

Hall dynamo peaks at resonant surface

but is spatially extended (8 cm ~ c/pi)

Ding,et al PRL,93,045002(2004)

Hall Term

€

E||+ ˜ v × ˜ B

||+

˜ j × ˜ B ||

ne= η j

||

Multiple reconnection leads to strong dynamo effects

• Left: Core m=1 tearing mode only• Right: Edge m= 0 mode driven by core mode

Strong ion heating is observedwith multiple reconnection

Two cases of sawtooth relaxation

Interplay between local and global effects

• Effects of line tied boundary conditions on kink mode & current sheet formation

• Scalings of reconnection rate w.r.t.current sheet length

• Experimental and numerical studies of driven vs spontaneous reconnection, multiple modes (MST)

• Nonlinear evolution of Parker instability (UNH)• Effects of boundary on driven reconnection rate (MRX)• Energy release in a line tied medium forced at

boundary (UW)

Theoretical studies on effects beyond MHD

• Analytical and numerical models of Hall physics

(PPPL, UW, UNH)• Theory for anomalous resistivity (UC, PPPL)• Measurements and kinetic theory of LHDW (PPPL)

• Simulation of e+e- reconnection (UNH)

Current sheets in line tied fields

• Solar, stellar, and accretion disc flares are powered by magnetic fields.

• Magnetic energy is tapped through resistive dissipation, but resistivity is very low.

• 2-stage release process: formation of intense current sheets followed by resistive decay.

• Reduced MHD treatment of a periodic plasma exist for singular kinked equilibria, but not for line tied plasma

• Simulated in astrophysically relevant line tied plasmas for unrealistically large resistivity.

Current sheet in bounded plasma has been theoretically studied

Transition from periodic to line tied condition

The mode eigenfunction slowly approaches the periodic case with increasing tube length

Progress in CMSO Reconnection Research

Experimental Progress• Identified possible causes of fast reconnection

– Hall effects observed through a quadrupole field account for thr high resistivity observed in the low collisionality regime.

– Magnetic LHDW fluctuations correlate well with resistivity enhancement Commonality with space observations seen => Collaboration with space physics community

• An experimental scaling obtained in the transition from collisional to collisionless regime

• Anomalous ion heating documented• Global boundary effects on reconnection studied

– by systematic change of boundary– in form of multiple reconnection process

Progress in CMSO Reconnection Research (II)

Theoretical progress

• Progress made for global reconnection theory– The study of line tying effects has been initiated – Theory of multiple site reconnection is being

formulated– Scaling reconnection rate in 2-fluid theory being

considered

• Analytical & numerical theory of local reconnection with anomalous resistivity developed

• Analytical theory for quadrupole field generation developed

• Analytical theory of lower hybrid drift instability carried out for the neutral sheet

Future plans for CMSO reconnection research

• Causal relationship between the observed Hall effects and magnetic fluctuations with fast reconnection will be studied– 3-D consideration

• Scaling laws for reconnection rateScaling laws for reconnection rate• Develop theory of line tied systems Develop theory of line tied systems • Guiding principles are sought for 3-D global reconnection

phenomena– Solar & space physics– Helicity conservation – Global energy flows– Magnetic stochasticity

• Particle acceleration and heating