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Magnetic Reconnection in Plasmas; a Celestial Phenomenon in the Laboratory. J Egedal, W Fox, N Katz, A Le, M Porkolab, MIT, PSFC, Cambridge, MA. Outline. The problem of magnetic reconnection Reconnection in the Versatile Toroidal Facility Experimental setup Experimental observation - PowerPoint PPT Presentation
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Magnetic Reconnection in Plasmas; a Celestial Phenomenon in the Laboratory
J Egedal, W Fox, N Katz,A Le, M Porkolab,
MIT, PSFC, Cambridge, MA
• The problem of magnetic reconnection
• Reconnection in the Versatile Toroidal Facility– Experimental setup
– Experimental observation
– Electron kinetic effects
• Wind satellite data from the deep magnetotail– Kinetic effects
• The new closed configuration in VTF
• Conclusions
Outline
The Versatile Toroidal Facility (VTF)
3.5 m
The Versatile Toroidal Facility (VTF)
The Versatile Toroidal Facility (VTF)
A new closed cusp by internal coil. Passing electrons &
spontaneous reconnection events.
Two different magnetic configurations
A open cusp magnetic field. Fast reconnection by trapped
electrons. Wind observation
Both configurations have Bguide and toroidal symmetry 2d
VTF open configuration plasmashave a trapping potential
Typical Parameters:ne ~ 2-3 1016 m-3
Te ~ 12 eV
Ti ~ 1 eV
Bt ~ 80 mT (800 G)
Bc ~ 0-10 mT
Open field lines intersect the vessel wall.
Electrons stream faster than ions, so plasma charges positive
Thermal electrons are electrostatically trapped
Reconnection drive
– Electric field induced by a central solenoid
– The solenoid is driven by an LC circuit
– Vloop ~ 100 V
Plasma response to driven reconnection
The electrostatic potential
Experimentalpotential,
+70 V
-70 V
2BE B
-v gB
Electron flow:
The electrostatic potential
Frozen in law isbroken where EB0
0 cusppolBE BE
Ideal Plasma:
BE
J Egedal et al., PRL 90, (2003)
The electrostatic potential
Frozen in law isbroken where EB0
0 cusppolBE BE
Ideal Plasma:
c
BE
eoc l
The size of the electron diffusion region is
δ
δ (c
m)
ρcusp
cgo BBl /
• Why is the experimental current density so small?
• Liouville/Vlasov’s equation: df/dt=0
• For a given (x0,v0), follow the orbit back in time to x1
• Particle orbits calculated using electrostatic
and magnetic fields consistent
with the experiment.
• Massively parallel code
evaluates f(x0,v0) = f(|v1|).
Kinetic modeling(1)
Computer Physics Communications , (2004)
0 – 12 kA/m2
• The current is calculated as
• Theory consistent with measurements
(B-probe resolution: 1.5cm)
Kinetic modeling(2)
3
|||| vv dfj
Theory
Experiment
• The problem of magnetic reconnection
• Reconnection in the Versatile Toroidal Facility– Experimental setup
– Experimental observation
– Kinetic effects
• Wind satellite data from the deep magnetotail– Kinetic effects
• The new closed configuration in VTF
• Conclusions
Outline
M. Øieroset et al. Nature 412, (2001)
M. Øieroset et al. PRL 89, (2002)
Wind satellite observations in distant magnetotail, 60RE
• Measurements within the ion diffusion region reveal: Strong anisotropy in fe.
M. Øieroset et al. Nature 412, (2001)
M. Øieroset et al. PRL 89, (2002)
Wind satellite observations in distant magnetotail, 60RE
• Measurements within the ion diffusion region reveal: Strong anisotropy in fe.
Log(f)
A trapped electron in the magnetotail
The magnetic moment:B
m
2
v 2
B
m
2
)v-v( 2||
2
• From Vlasov’s equation df/dt=0 f(x0,v0) = f(Eexit )
• Two types of orbits:
Drift kinetic modeling of Wind data
Passing: Trapped : =mv2/(2B)+… is constant
maxmin|| /1cos
v
vBBc
c
No cooling Cooling
• Applying f(x0,v0) = f(|v1|) to an X-line geometry consistent with the Wind measurements
• A potential, needed for trapping at low energies
• Ion outflow: 400 km/s, consistent with acceleration in
Drift kinetic modeling of Wind data
~ -300V~ -800V~ -1150V
Theory Wind
Phys. Rev. Lett. 94, (2005) 025006
• Applying f(x0,v0) = f(|v1|) to an X-line geometry consistent with the Wind measurements
• A potential, needed for trapping at low energies
• Ion outflow: 400 km/s, consistent with acceleration in
Drift kinetic modeling of Wind data
Theory Wind
Phys. Rev. Lett. 94, (2005) 025006
~ -1150V
f(x0,v0) = f(E0-q0), passing
= f(B), trapped
Cluster Obs.
• The problem of magnetic reconnection
• Reconnection in the Versatile Toroidal Facility– Experimental setup
– Experimental observation
– Kinetic effects
• Wind satellite data from the deep magnetotail– Kinetic effects
• The new closed configuration in VTF
• Conclusions
Outline
New closed magnetic configurations
A new reconnection drive scenario
Spontaneous reconnection
Phys. Rev. Lett. 98, (2007) 015003
Sweet-Parker is out, E ≠ *j !
Current channel expelled, J
Magnetic energy released
R
Bz
vA ~ 10 km/s
c/pi ~ 1m, s ~ 0.12m
4
-4
t [µs]d
/dt [
V]
What Triggers Reconnection? R
[m
]
t [µs]Mode at f=50 kHz
d/dt [V]R
Plasma outflows
Rough energy balance
• Magnetic energy released ~ 0.5 × 6 10-6 H × (500A)2 ~ 0.8 J
• Electron energization ~ 500 A × 80V × 2 10-5s ~ 0.8 J
• Ion flows: ~ 24 eV × 21018m-3 ×0.06m3 ~ 0.48 J
Strong energizations of the ions
Electrostatic (and magnetic) fluctuations observed during reconnection events
Loop voltage (V)
Fluctuation > 10 MHz (au)
Spectrogramf (MHz)
0 1t (ms)[Mar 22 shot 405,HPF 80kHz, scope B/W 150 MHz]
fLH ~ 10 MHz
fpi ~ 30 MHz
(off scale)
fpe ~ 10 GHz
fce ~ 1 GHz
800
0Plasma Current (A)
Conclusions– Fast, collisionless driven reconnection observed in the
open cusp configuration– Classical Coulomb collisions are not important– The width of the diffusion region scales with cusp
– Solving Vlasov’s equation (using the measured profiles of E and B) provides current profiles consistent with the VTF measurements; the current is limited by electron trapping.
– Wind observations consistent with fast reconnection mediated by trapped electrons
– New closed configuration in VTF provides exciting
new parameter regimes and boundaries for future study of collisionless magnetic reconnection & the trigger problem.
Thank you for your attention
Future studies with the new configuration• Fast, bursty reconnection with closed boundaries and in the
presence of guide magnetic field can be studied (for the first time)
• What controls the rate of reconnection?
• How is reconnection “triggered”
• Huge parameter regime available: Scans possible in Bcusp, Bguide, Te, Ne, Erec.
• Spans collisional to collisionless regimes: e = 0.1 – 103 m
• High plasma pressure (compared to magnetic field): ~ 1
• Warm and magnetized ions.
• 3D magnetic geometries are easily implemented
Upgrade of open Cusp
Existing configuration Fields of new in-vessel coils
Upgrade of open Cusp
New total field
Ionization region
Reconnection Experiments with a Guide Magnetic Field
J Egedal, W Fox, N Katz, A Le and M Porkolab
MIT, PSFC, Cambridge, MA