MRX has received significantly stronger DOE support

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Experimental Study of Two-Fluid Physics of
Magnetic Reconnection In Laboratory and Space
Plasmas
Masaaki Yamada Princeton Plasma Physics
Laboratory
In collaboration with Hantao Ji, Russell Kulsrud,
Stefan Gerhardt, Alex Kuritsyn, and Yang Ren

at IPELS 2005, July 5, 2005 Tromso, Norway
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Outline

• Goal -Highlight the recent measurements of
  two-fluid effects during magnetic reconnection in
  MRX and compare them with space observations
• 1. Local vs global issues
• Global boundary conditions influence or determine
  local reconnection dynamics -gt driven
  reconnection
• Local sheet physics influences global topology
  evolution -gt spontaneous reconnection
• 2. Two-fluid dynamics of local reconnection layer
• Fine structure of the neutral sheet
• Hall term effects
• Classical collisions vs non-classical collisions
  (fluctuations

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Magnetic Reconnection in Solar flares

• We see clear global reconnection through topology
  changes.
• It is not easy to identify local reconnection
  regions

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Identification of a local reconnection
region Two-Fluid Hall effects were documented in
the current sheet of the magnetopause
d c/wpi
Mozer et al., PRL 2002
POLAR satellite
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Two Fluid Physics Issues been addressed in
dedicated lab experiments

• Current sheet profiles
• ? c/?pi, consistent with theory MRX, SSX,
  TS-3, Space data
• B ? tanh(x/?), in MRX, VTF, Polar Geotail etc
• Reconnection rate
• - Enhanced in less collisional MRX, TS-3 and
  collisionless VTF regimes
• Focus of this talk gtTwo-fluid effects in MRX
• Hall Effects
• Out-of-plane quadrupole field
• Fluctuations
• Detected by electrostatic and magnetic probes.
• Magnetic fluctuations around Lower Hybrid
  frequency and the waves correlate well with the
  resistivity enhancement MRX ltgt WIND, GEOTAIL,
  Cluster

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MRX upgraded in 2004

• Relocated the PF and TF power supplies, increased
  stored energy (500 kJ)
• Extended vacuum vessel to allow greater flux-core
  separation

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Study of Reconnection Rate vs Boundary Conditions
(Z0 scan)
Z0

• Z0 scan
• Changing the distance between the flux cores
• Collisional regime (Resistive MHD)
• Low collisional regime (Non-classical)

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Current Sheet Length Becomes Longer at Larger
Flux Core Separation
Z060cm
Z035cm
L7cm
L15cm
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Reconnection speed in MRX does not agree with
classical Sweet-Parker theory
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Outflow Speed Measured by Mach Probe
Downstream pressure impedes the outflow
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(No Transcript)
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Resistivity is Determined by Local Plasma
Parameters
Without guide field Kuritsyn, 05
Local reconnection model works Resistivity is
enhanced in low collisional plasmas for ?mfp gt
c/?pi
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Comparison of Resistivity With and Without Guide
Field
Kuritsyn 2005

• The results are in consistent with Spitzer
  resistivity
• gt Local reconnection model is working

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Approach to Physics of Magnetic Reconnection
Layer (I)
One Fluid MHD
Sweet-Parker model Petchek model
Limitation
If not satisfied, instability would enhance ?
If not satisfied, electrons motion
decouples from ions
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Approach to Physics of Magnetic Reconnection
Layer (II) Hall Term is dominant in most of the
reconnection experiments
Generalized Ohms law
gtgt 1
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Two competing models to explain fast reconnection
Generalized Sweet-Parker model
2-Fluids MHD Model
We observe both!
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Hall term should play a major role in force
balance in y direction (Breslau)
hj
E v ? B
(j ? B)/nee


?2?10-3 ?10-2 c/?pi2.277?10-2
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Very Fast Electron Flow
Breslau
flux contours
separatrix
ion flow
electron flow
symmetry axes
c/?pi-gt
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).
?2?10-3 ?10-2 c/?pi2.277?10-2
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A wide array of magnetic probes allow
reconstruction of the reconnecting current sheet
New fine structure probe 71 channels
Profile of the neutral sheet has been measured d
0.4 c/wpi.
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The Fine Structure Probe allows measurements
within the current sheet with 1.25 mm resolution
5 cm
c/?pi 2-10 cm. c/?pe .5-2.5 mm.
1.25 mm
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Out-of-plane Quadrupole has been predicted by
numerical simulations
By
By
Bz
Bz
From Drake et al.
By
x/di
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Toroidal quadupole field is found in off axis
locations demonstrating 2 Fluid MHD effects
Probe at z -7 cm
Probe at z 7 cm
Fine Structure Probe ? 1mm
R
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2-D display of Hall toroidal field contours (in
colors)with reconnecting field vectors(? x4cm,
? z1cm)
Movie is available
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Experimentally measured 3-D field line features
in MRX

• Manifestation of Hall effects in MRX
• Electrons would pull magnetic field lines with
  their flow

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Self-made quadru-pole field size versus fill
pressure Collisions reduce the Hall effects
Bz is the shoulder value of reconnecting field.
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Identification of a local reconnection
region Two-Fluid Hall effects were documented in
the current sheet of the magnetopause
d c/wpi
Mozer et al., PRL 2002
POLAR satellite
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Cluster Observation of Hall Effects
Vaivads et al. PRL04
Quadrupole signature was observed in current
sheet in high latitude magnetopause
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Fast Reconnection ltgt Enhanced Resistivity

• Main question
• What is the cause of the observed enhanced
  resistivity?
• Collisional effects are not dominant in low
  density regime (Te gt 6 eV, ne lt 5x1013 cm-3)

• Hall MHD Effects
• Electromagnetic Fluctuations
• Both Observed in MRX

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Magnetic Fluctuations Measured in Current Sheet
Region
(Ji et al. PRL, 04)

• Comparable amplitudes in all components
• Waves wereidentified as a branch of Whistler
  waves

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Magnetic Fluctuations Peak Near the Current Sheet
Center
gt R. Kulsruds Talk
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Global Stability Analysis of Harris Sheet
(Huba, Drake, Gladd, 80) (Yoon, Lui, Sitnov,
02) (Daughton, 03)
2-fluid treatment (Yoon et al, 02)
Full kinetic treatment (Daughton 03)
EM component at center and ES component at edge
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Similar Observation by Spacecraft at Earths
Magnetopause
(Phan et al. 03)
(Bale et al. 04)
EM
ES
high b
low b
high b
low b
low b
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Amplitudes of whistler waves correlate well with
resistivity enhancement in MRX
Ji et al., To be published in PRL, 03
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Linkage between space and lab scales on
reconnection
Indicates importance of 2-fluid effects
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How do 2-fluid effects come into play?
MRX scaling of reconnection rate w.r.t.
Normalized ion skin depth
Breslau
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Summary

• Significant progress has been made in laboratory
  reconnection experiments and space observations
  gt joint study of local physics mechanisms
• Important progress In lab experiments for local
  physics issues,
• Transition from collisional to collisionless
  regime documented
• Hall MHD effects identified through measurement
  of out-of-plane quadrupole field
• Electromagnetic fluctuations with w wlh have
  been observed in the MRX current sheet and
  correlate with resistivity enhancement
• Relative drift of electrons seems to be a
  dominant driving force- modified two stream
  instability
• Significant commonality found between lab results
  and space observations
• Analytical study of local reconnection physics is
  now essential