Progress and Planson Magnetic Reconnection for CMSO
M. Yamada, C. Hegna, E. Zweibel
For General meeting for CMSOAugust 4, 2004
1. Recent progress and plansExperiment-YamadaTheory-Hegna, Malshkin, Lazarian
2. Discussions on Plans
Experimental Progress and Plans Outline
-Recent progress by CMSO research and its relationship to space physics
• Understanding of local reconnection physics advanced- 2 Fluids MHD- Hall MHD physics- EM Fluctuations: Whistler waves- Current sheet profiles
• Global reconnection physics being developed- Plasma merging
• Plans- 2 Fluids MHD physics study will continue- Role of reconnection in dynamos and ion heating
Four devices [MRX, MST, SSX, and SSPX] are available for reconnection research in CMSO
MRX
SSX
MST
SSPX
Global reconnection sequence in solar flare
• Observation by Yokoyama et al, Vrecc/VA ~ 0.002- 0.011
Current Physics Issues on Magnetic Reconnection
1. Local vs global physics– Global boundary conditions influence or determine
local reconnection dynamics or forced reconnection– Local sheet physics influences global topology
evolution and relaxation rate
2. Collisional vs collisionless reconnection– Classical collisions and non-classical collisions
(fluctuations)– Hall term effects
Global Reconnection Physics Results from Recent Laboratory Experiments
• Plasma Merging– Counter-helicity merging rate >> Co-helicity merging rate
[TS-3, SSX, MRX] • Magnetic helicity conservation
– Helicity conservation studied [TS-3]– Flux inventory during reconnection [MST, SSPX]
• Identification of Hall dynamos in MST => Dynamo session
• There are very few quantitative data from space to verify the above results, but there are many interesting implications
Local issue; Two competing models to
explain fast reconnection
• 1-Fluid MHD model + effective resistivity (Effects of waves)
•2-Fluids MHD; decoupling of ions and electrons within the ion skin depth, cpi; -> Including the Hall term, jexB
Dedicated lab experiments [LLPD(EMHD), MRX, SSX, TS-3, VTF etc.]
Generalized Sweet-Parker model Petschek-type Model
2-D numerical simulation can assess 2-fluids effects
Je
Ji
Vi
Jpne
1BJ
nec
1Bv
c
1E
dt
Jd4ei2
pe
Below c/pi electron and ion motion decouple•electrons frozen-in to B
•Observed out-of-plane quadrupole fields•Obtained a thin electron current layer of c/pe
Drake et al
These results have not been verifiedin lab experiments
A force valance observed in the MRX shows a strong effect of Hall term
• A force balance in incoming (x) direction would give;
Jy x Bz = px
or [p + Bz2]/20 ~ const.
Generalized Ohm’s law: Jpne1
BJnec1
Bvc1
EdtJd4
ei2pe
Phys. Plasmas, v. 7, 1781 (2000)
Contour; E + v B
=210-3; =10-2; c/pi=2.27710-2
2 Fluid TheoryBreslau et al., 2004
E + vxB ~ 0
E = const.
Steady state dB/dt =Curl E
c/pi
Hall term should play a major role in force balance
=210-3; =10-2; c/pi=2.27710-2
E + v B (j B)/neej= +
Fluid Flow Lines
=210-3; =10-2; c/pi=2.27710-2
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).
c/pi
2D Current Profile with Hall Term and Elevated Resistivity
=10-2;=10-2; c/pi=2.27710-2
Major Goals for Magnetic Reconnection in CMSO
• 1) Study 2-fluid MHD effects through the generalized Ohm’s law in the reconnection region and determine the role of turbulence in reconnection process.
• 2) Find key relationships between the local physics of the reconnection layer and the dynamics of global plasma reconnection phenomena.
• 3) Identify key 3-D effects on reconnection, whether intrinsic or due to boundary conditions.
• 4) Evaluate the role of magnetic reconnection in dynamos, ion heating, and, more generally, in other magnetic self-organization phenomena.
The measured current sheet profiles agree well
with Harris theory
(MRX dataPhys. Plasmas, 7, 1781, 2000)
Sheet width agrees with Harris model demonstrating 2-fluid MHD effects
• scales with c/pi
~ constant vd/vthe
• is not determined by Sweet-Parker thickness
Reconnection speeds up drastically in low collisionality regime
What causes the anomalous resistivity?M
easu
red
resi
stiv
ity
Trintchouk et al, PoP 2003
Collisionality
Reconnection rate is enhanced for (c/pi)/sp >1
Breslau et al,
)10( 314* cmns
ei
V
VV
17103 810 1410
810 610
810 510 1310
2/1
*
*4/3
*
*
2/1ln
57.6
L
B
n
T
V
VV
s
ei
spH
ei
iie
piH VV
mTTc
2
S
Lsp S
System L* (10cm) B* (100G) T* (10ev)
MRX 1 1 1 1 2.04
Astrophysics 0.1 0.0014
Solar Flares 1 10 26.53
Magnetosphere 1 2320
Tokamak 10 100 1 1000 893.6
, which comes from , where , and is the
Lundguist number.
If Ratio of the Sweet-Parker thickness to the Ion Inertia Length, = 1
Measurements of Diffusion Regionwith a Hall effect signature
Mozer et al., PRL 2002
POLAR satellite
A reconnection layer has been documented in the magnetopause
Fast Reconnection <=> Enhanced Resistivity
• Main question
– What is the cause of the observed enhanced
resistivity?
• Electrostatic Turbulence
• Electromagnetic Fluctuations
• 2 Fluids effects
» All effects may be coupled in MRX
Turbulence Amplitudes Correlate with Resistivity Enhancement
MRX has been upgraded to address major reconnection physics issues in collision-less regime
Lager S number expected with higher B and Te
New fine structure probe
71 channels
Vacuum vessel extended
Initial measurement of fine structure of the neutral sheet
Confirms the previously seen Harris current sheet profile.
As the current sheet thins, deviations from the Harris tanh profile are seen in a transient phase.
Magnetic reconnection in MST Two fluid effects can significantly alter the
reconnection and dynamo, for < c/pi
j ˜ v ˜ B ˜ j ˜ B
neMHD term Hall term
S. Prager’s talk
Hall dynamo large near resonant surface
PRL July 23, 2004
SSX- Merging Experiments
/
Mode I
Mode II
Generalized Ohm’s Law has been addressed in SSX
• JxB term is evaluated to be much larger than collisional resistivity term and inertia term
[Cothran et al. to be submitted to GRL]=> M. Brown’s talk
Magnetic structure consistent with FRC/doublet-CT
SSX (Swarthmore) 2002
•Reversed field•Very little midplane toroidal field•Axially antisymmetric B•70 G RCC field (on axis)
Summary
Progress being made in laboratory experiments
• Transition from Sweet-Parker (collisional) to 2-fluid MHD regime documented ; A new scaling found
• Hall effects have been experimentally studied in the neutral sheets [MRX, SSX] as well as in the unstable flux surfaces [MST]
• Magnetic turbulence [whistler waves] identified in the neutral sheet, correlates well with resistivity enhancement
• With regard to the fine properties of the neutral sheet, a close interrelationship to space observations (in the magnetosphere) has been established; WIND, GEOTAIL, Cluster
• Conclusive guiding principles may be yet to be found in reconnection with global reconnection– Magnetic helicity, 2 fluids effects
Short-Intermediate Term Research Objectives
• 1) Investigate local dynamics in the vicinity of the neutral sheet to assess 2-fluid MHD processes, such as Hall and turbulence effects.
• 2) Explore the relationship between anomalous ion heating and reconnection events in both laboratory and astrophysical plasmas, and investigate why Ti is
generally higher than Te in reconnection region.
• 3) Investigate how the local reconnection process is related to global reconnection and dynamo activity.
• 4) Role of reconnection in dynamos
Local Reconnection Physics Results from Recent Laboratory Experiments
• Current sheet profiles ~ c/pi, consistent with theory; MRX, SSX, TS-3, GEOTAIL, WINDS
– B tanh(x/), in MRX, VTF, agrees with space data [ Mozer et al.]
• Reconnection rate– Consistent with a generalized Sweet-Parker Model [MRX]
• Plasma resistivity– Verification of Spitzer perpendicular resistivity in collisional limit
[MRX]
– Enhanced in less collisional [MRX, TS-3] and collisionless [VTF] cases
• Fluctuations– Detected by electrostatic and magnetic probes [MRX, VTF]
– Magnetic fluctuations around Lower Hybrid frequency correlate well with the resistivity enhancement [MRX] <=> WIND, GEOTAIL, Cluster
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