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 • Electron kinetic effects • Wind satellite data from the deep magnetotail • Kinetic effects • The new closed configuration in VTF • Conclusions
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 Open field lines intersect the vessel wall. Electrons stream faster than ions, so plasma charges positive Thermal electrons are electrostatically trapped Typical Parameters: ne ~ 2-3 1016 m-3 Te ~ 12 eV Ti ~ 1 eV Bt ~ 80 mT (800 G) Bc ~ 0-10 mT
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
Electron flow: Experimental potential, The electrostatic potential +70 V -70 V
The electrostatic potential Ideal Plasma: Frozen in law is broken where EB0
The size of the electron diffusion region is J Egedal et al., PRL 90, (2003) The electrostatic potential Ideal Plasma: δ Frozen in law is broken where EB0 δ (cm) ρcusp
Kinetic modeling(1) • 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|). Computer Physics Communications , (2004)
Kinetic modeling(2) 0 – 12 kA/m2 • The current is calculated as • Theory consistent with measurements (B-probe resolution: 1.5cm) Theory Experiment
Outline • 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
Wind satellite observations in distant magnetotail, 60RE M. Øieroset et al. Nature 412, (2001) M. Øieroset et al. PRL 89, (2002) • Measurements within the ion • diffusion region reveal: • Strong anisotropy in fe.
Wind satellite observations in distant magnetotail, 60RE M. Øieroset et al. Nature 412, (2001) M. Øieroset et al. PRL 89, (2002) • Measurements within the ion • diffusion region reveal: • Strong anisotropy in fe. Log(f)
A trapped electron in the magnetotail The magnetic moment:
No cooling Cooling Drift kinetic modeling of Wind data • From Vlasov’s equation df/dt=0 f(x0,v0) = f(Eexit ) • Two types of orbits: Passing: Trapped : =mv2/(2B)+… is constant
Drift kinetic modeling of Wind data • 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 Theory Wind ~ -1150V ~ -300V ~ -800V Phys. Rev. Lett. 94, (2005) 025006
f(x0,v0) = f(E0-q0), passing = f(B), trapped Drift kinetic modeling of Wind data • 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 Theory Wind ~ -1150V Cluster Obs. Phys. Rev. Lett. 94, (2005) 025006
Outline • 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
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 Bz R 4 -4 vA ~ 10 km/s c/pi ~ 1m, s ~ 0.12m
d/dt[V] t [µs] Mode at f=50 kHz What Triggers Reconnection? R d/dt [V] R [m] t [µs]
Plasma outflows
Rough energy balance • Magnetic energy released ~ 0.5 × 6 10-6 H × (500A)2 ~ 0.8 J • Electron energization ~ 500 A× 80V × 210-5s ~ 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 800 0 Plasma Current (A) Loop voltage (V) Fluctuation > 10 MHz (au) (off scale) fpe ~ 10 GHz fce ~ 1 GHz f (MHz) Spectrogram fpi ~ 30 MHz fLH ~ 10 MHz 0 t (ms) 1 [Mar 22 shot 405, HPF 80kHz, scope B/W 150 MHz]
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 Fields of new in-vessel coils Existing configuration
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
