Transcript MRX has received significantly stronger DOE support

Progress and Plans
on Magnetic Reconnection for CMSO
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
For NSF Site-Visit for CMSO
May1-2, 2005
Magnetic Reconnection
Before reconnection
•
•
•
After 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?
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
Vin
Vout» Va
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).
J  B  p me dVe
E  V  B  J 
 2
en
e 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
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)
Measurement
•
Simulation
Good agreement between the measurement and the simulation
(yellow region).
Striking similarities with the the data from the magnetopause
d ~ c/pi
Mozer et al., PRL 2002
POLAR satellite
EM & ES fluctuation profiles are very similar
MRX Scaling:
A linkage between space and lab on reconnection
Breslau
di/ dsp
~ 5( mfp/L)1/2
MRX scaling shows transition from the MHD (collisional) to
2 fluid regime based on normalized ion skin depth
Quadrupole out-of-plane field
has 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
60
< dJxdB>// /nee
[V/m]
40
20
E ||  v˜  B˜ || 
˜j  B˜
||
ne
 j
0
||
0.4
0.8
r/a
Hall Term
Hall dynamo peaks at resonant surface
but is spatially extended (8 cm ~ c/pi)
Ding,et al PRL,93,045002(2004)
Multiple reconnection leads to strong dynamo effects
Two cases of sawtooth relaxation
Strong ion heating is observed
with multiple reconnection
• Left: Core m=1 tearing mode only
• Right: Edge m= 0 mode driven by core mode
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 rate
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