MRX has received significantly stronger DOE support

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Experimental Study Plans of MRX for Two-Fluid
Physics of Magnetic Reconnection
Masaaki Yamada
August 12 2005
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Outline

• - Highlight the recent measurements of
  two-fluid effects seen in MRX and compare them
  with space observations
• 2 fluid effects observed in local reconnection
  physics studies to date
• Current sheet profiles with high resolution (?x
  c/?pe)
• gt Harris sheet Quadrupole
• Hall Effects Out-of-plane quadrupole
  fieldFluctuations
• How to make a combined pictures
• Pressure tensor term
• Comparison with space observations
• Polar satellite results with out of plane
  quadrupole field

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Two competing models to explain fast local
reconnection
Generalized Sweet-Parker model
Petschek-type Model
Dedicated lab experiments LLPD(EMHD), MRX, SSX,
TS-3, VTF etc.
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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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A force balance observed in the MRX shows an
effect of Hall MHD term
Generalized Ohms law

• A force balance in incoming (x) direction would
  give
• Jy x Bz ?px
• or p Bz2/2m0 const.

Phys. Plasmas, v. 7, 1781 (2000)
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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
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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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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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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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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Measured Off-Center Reconnecting Magnetic Field
and simulation result
Bz
r/di
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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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Hall Term is dominant in most of the reconnection
experiments
Generalized Ohms law
gtgt 1
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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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Measured resistivity scales with regard to system
size

• Recent observation from Kuritsyn et al, d ? L

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Linkage between space and lab scales on
reconnection
Indicates importance of 2-fluid effects
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Push reconnection (merging) experiment in MRX
Push reconnection involves toroidal
(out-of-plane) field. ? Two cases of counter
helicity exist. Counter helicity Normal
- Flipped -
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Flux plots (Normal counter helicity)
X-point is pushed in when strong Bt comes.
BtltBr
BtBr
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Flux plots (Flipped counter helicity)
X-point is pushed out when strong Bt comes.
BtltBr
BtBr
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Interpretation of this phenomena(a) deference of
X-point position _at_250msec
A simple two fluids model in which field line is
frozen in electron fluids explains these
observations well.
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Is flux plot reliable?
Direct evidence may be preferable because flux
plot is somewhat artificial.
1d probe measurement shows a good agreement with
the model (or flux plot).
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1d plot signal during merging
Same trend is observed during merging, although
reproducibility and axisymmetry are not good
(flux plot is not available). (These shots were
taken by Alex for IDSP measurement.) Here,
290msec is the time when radial ion flow becomes
largest for Normal case.
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New measurement push probe
New push probe may bring detailed shape of
current sheet (V- or -shape) or quadrupole
structure in early reconnection
phase. Existing 1d probe Chord-averaged
spectroscopy or IDSP may be enough to verify or
modify the two fluid model?