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Results from Magnetic Reconnection Experiment
And Possible Application to Solar B program
Masaaki Yamada
Princeton University, PPPL
In collaboration with Y. Ren, H. Ji, S. Gerhardt, R. Kuslrud, and A. Kuritsyn
For Solar B Science meeting,
Kyoto, Japan
November 8-11, 2005
Various “Flares” (Reconnection Phenomena)
X-ray
intensity
Solar flare
time(hour)
Magnetospheric
Aurora-substorm
Magnetic
Field
strength
time(hour)
Laboratory
reconnection
Magnetic
Field
strength
time(μsec)
Tokamak
disruption
Electron
temperature
time(sec)
Protostellar
flare
X-ray
intensity
time
105 sec
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
Self-organization Processes
External Energy Source
Dynamo
Magnetic reconnection
Magnetic chaos & waves
Angular momentum transport
Ion Heating
Magnetic helicity conservation
Unstable Plasma
State
• 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 a
Sorenson Video 3 decompressor
are needed to see this picture.
reconn << SP
Local view of
reconnection in
a tokamak
From H. Park
QuickTime™ and a
Video decompressor
are needed to see this picture.
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
2-D
3-D
TS-3/SSX
local
boundary
steady state
process
collisionless
collisionality
global
transient
collisional
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 reconnection
Global 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
QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this picture.
The measured current
sheet profiles agree well
with Harris theory
(Yamada et al.,Phys. Plasmas, 7, 1781, 2000)
Resistivity Enhancement Depends on Collisionality
E  VR  BZ   j
* 
E
j
Agreement with a Generalized
Sweet-Parker Model
(Ji et al. PoP ‘99)
• The model modified to take
into account of
– Measured enhanced
resistivity
– Compressibility
– Higher pressure in
downstream than upstream
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
Vin
Vout» Va
Generalized Sweet-Parker model
with anomalous resistivity.
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
The Hall Effect During Reconnection Shown
in 2D Simulation
•
The blue lines show the ion flow streamlines.
•
The red arrows show the electron flow.
•
The black lines show the magnetic flux.
Different motions of ions and electrons
In-plane current
A out-of-plane quadrupole magnetic field
The colors show the out-of-plane
quadrupole magnetic field.
2-fluid MHD simulation performed by J.
Breslau with the 2-D Magnetic Reconnection
Code (MRC).
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
c/pi
≈ 2-10 cm.
c/pe
1.25 mm
≈ .5-2.5 mm.
Fine Structure
Probe [∆ =1mm]
MRX Data
Experimentally measured
3-D field line features in MRX

e flow
• Manifestation of Hall effects in MRX
• Electrons would pull magnetic field lines with their flow
Evolution of magnetic flux contours during MRX reconnection
A reconnection layer has been documented in the magnetopause
d ~ c/pi
Mozer et al., PRL 2002
POLAR satellite
The Electron Flow Velocity is Deduced
Separatrix
•
Measurement
•
Simulation
Good agreement between the measurement and the yellow
region in the 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
regime
mfp < d
Collisionlessl regime
mfp > d
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 Hall term is important
when |d/mfp|<1.
Collisionless
Collisional
•
The ratio between the jrx Bz/ene
and the reconnection electric field
is evaluated.
•
The d/mfp denotes the
collisionality of plasmas.
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
(Bale et al. ‘04)
(Phan et al. ‘03)
EM
ES
low high low
b
b
b
low
b
high
b
A linkage between space and lab on reconnection
Breslau
MRX scaling shows transition from
collisional (MHD) regime to 2 fluid
MHD regime
w.r.t. normalized ion skin depth
di/ dsp
~ 5( mfp/L)1/2
System
L (cm)
B (G)
MRX/SSX
10
100-500
MST
30/100
1-3x103
Magnetosphere
109
10-3
Solar flare
109
ISM
1018
100
10-6
Protostar d / d >> 1
d i=
c/pi(cm)
1-5
dsp (cm)
di/ dsp
0.1-5
.2-100
10
0.1
100
107
104
>103
104
102
100
107
1010
0.001
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 checked in a broader basis
using di/dSP in the transition from collisional to collisionless
regimes
• Effects 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 coronae
Global Physics
for Helicity
Counter-helicity
merging generates
FRC and strong
ion heating
TS-3 Data