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Experimental Study of Magnetic Reconnection and Dynamics of Plasma Flare Arc in MRX Masaaki Yamada. Center for Magnetic Self-organization PPPL, Princeton University. August 3 2009 2009 SHINE Meeting at Nova Scotia. In collaboration with E. Oz, J. Xie, D. Lecoanet and H. Ji. Recent Progress. - PowerPoint PPT Presentation
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Experimental Study of Magnetic Reconnection and Dynamics of Plasma Flare Arc in MRX
Masaaki Yamada
August 3 20092009 SHINE Meeting at Nova Scotia
Center for Magnetic Self-organization
PPPL, Princeton University
In collaboration with E. Oz, J. Xie, D. Lecoanet and H. Ji
Recent Progress
Experimental study of the reconnection layer on MRX=> Fast reconnection in collsionless regime is determined by
Hall effects except the e-diffusion regime
– Two-scale diffusion region
– Thickness of the electron diffusion layer > c/pe
• MRX scaling in transition from MHD to 2-fluid regime
• New results from our solar flare experiments
Experimental Setup and Formation of Current Sheet
Experimentally measured flux evolution
ne= 1-10 x1013 cm-3, Te~5-15 eV, B~100-500 G,
Neutral sheet Shape in MRXChanges from “Rectangular S-P” type to “Double edge X” shape as collisionality is reduced
Rectangular shapeCollisional regime: mfp <Slow reconnection
No Q-P field
Collisionless regime: mfp > Fast reconnection
Q-P field present
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
X-type shape
<= Ma & Bhattacharjee ,’96
Fast Reconnection <=> Hall Effects
=>
• Hall Effects create a large E field (except at X point)
• e-i collisions ~ small
• A major question
=> What is a scaling law w.r.t. collisionality
MRX scaling shows a transition from the MHD to 2 fluid
regime based on (c/pi)/ sp
MRX Scaling: * vs (c/i)/ sp
Breslau
A linkage between space and lab on reconnection
Hall MHD
η* ≡Eθjθ
No
ma
lize
d b
y S
pitz
Yamada et al, PoP, 2006
€
=4.5λmfpL
⎛
⎝ ⎜
⎞
⎠ ⎟
1/ 2mimiH
⎛
⎝ ⎜
⎞
⎠ ⎟
1/ 4
€
cωpi
1
SPδ
Anatomy of MRX Scaling
In the outside of the e-diffusion region, reconnecting field Ey is primarily determined by jHall xB:
€
E =η s j
EHall =jH × B
ne
η eff =jH × B
nej0
⎛
⎝ ⎜
⎞
⎠ ⎟
whereη S =mvene2λ mfp
η effη S
=BHBo
mime
⎛
⎝ ⎜
⎞
⎠ ⎟
1/ 2λ mfpL
Collisional resistivity
MRX Scaling: eff linearly increases with mfp/L
€
effη S
=BHBo
mime
⎛
⎝ ⎜
⎞
⎠ ⎟
1/ 2λ mfpL
Hall effects:
Next Step=> Add guide field
Main Objectives(1) To determine stability conditions for a single flux
rope as a function of field line twist, q, curvature, and the “strapping”field,
(2) To evaluate the effects of line tying for flux rope plasma
(3) To measure the magnetic energy transfer to the plasma during magnetic self-organization (eruption)
Solar Flare Experiment on MRX
electrodes
D
flare
Magnetic probes
MRX vacuum vessel
Equilibrium Field
Equilibrium Field CoilsGuide Field
Coils
`
` Guide Field
D: 2R FLARE Diametera: Flare radius
a
Experimental Setup
Electrodes inside the MRX vacuum vessel
Flare photos taken with a commercial Canon Powershot 100 µs exposure
STABLE
UNSTABLE
Cathode
Anode
•Bt = 1.06 kG
q<1
q>1
Kink instability
•Bt = 0.36 kG
•Electrode angle ~90o
Stability Condition for a Partial Arc
1
180o
•=> line-tying effects?
•The data shows that the stability condition for a simple toroidal q value without line-tying effects describes the experimental data.
•R=20, a =7 cm
Magnetic Relaxation is observed
Taylor State: ~ constant
Magnetic relaxationRFP toroidal plasmas
Summary
• Hall effects facilitate fast reconnection in MRX• Transition from collisional MHD to two-fluid regime
=> changes the neutral sheet profile and the reconnection rate
• A new scaling found on reconnection rate
• A new experimental campaign has started to study the dynamics of solar flares (=> Oz, Poster)