Progress and Plans on Magnetic Reconnection for CMSO For NSF Site-Visit for CMSO May1-2, 2005 1....
Transcript of Progress and Plans on Magnetic Reconnection for CMSO For NSF Site-Visit for CMSO May1-2, 2005 1....
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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
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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
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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.
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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
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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
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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
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Two types of reconnection layer profiles observed in MRX
• High density collisional regime
• Low density collisionless regime
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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
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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)
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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
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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
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Quadrupole out-of-plane fieldhas been reported by SSX push reconnection
experiment
Ion inertial scale 2 cm
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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
||
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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
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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)
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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)
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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.
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Current sheet in bounded plasma has been theoretically studied
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Transition from periodic to line tied condition
The mode eigenfunction slowly approaches the periodic case with increasing tube length
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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
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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
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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