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)

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 B guide and toroidal symmetry  2d

VTF open configuration plasmas have a trapping potential Typical Parameters: n e ~ m -3 T e ~ 12 eV T i ~ 1 eV B t ~ 80 mT (800 G) B c ~ 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 – V loop ~ 100 V

Plasma response to driven reconnection

The electrostatic potential Experimental potential,   +70 V -70 V Electron flow:

The electrostatic potential Frozen in law is broken where E  B  0  Ideal Plasma:

J Egedal et al., PRL 90, (2003) The electrostatic potential Frozen in law is broken where E  B  0  Ideal Plasma: The size of the electron diffusion region is δ δ (cm) ρ cusp

Why is the experimental current density so small? Liouville/Vlasov’s equation: df/dt=0 For a given (x 0,v 0 ), follow the orbit back in time to x 1 Particle orbits calculated using electrostatic and magnetic fields consistent with the experiment. Massively parallel code evaluates f(x 0,v 0 ) = f  (|v 1 |). Kinetic modeling (1) Computer Physics Communications, (2004)

0 – 12 kA/m 2 The current is calculated as Theory consistent with measurements (B-probe resolution: 1.5cm) Kinetic modeling (2) 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, 60R E Measurements within the ion diffusion region reveal: Strong anisotropy in f e.

M. Øieroset et al. Nature 412, (2001) M. Øieroset et al. PRL 89, (2002) Wind satellite observations in distant magnetotail, 60R E Measurements within the ion diffusion region reveal: Strong anisotropy in f e. Log(f)

A trapped electron in the magnetotail The magnetic moment:

From Vlasov’s equation df/dt=0  f(x 0,v 0 ) = f  ( E exit ) Two types of orbits: Drift kinetic modeling of Wind data Passing: Trapped :  =mv  2 /(2B)+… is constant No coolingCooling

Applying f(x 0,v 0 ) = f  (|v 1 |) 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 TheoryWind Phys. Rev. Lett. 94, (2005)

Applying f(x 0,v 0 ) = f  (|v 1 |) 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 TheoryWind Phys. Rev. Lett. 94, (2005)   ~ -1150V f(x 0,v 0 ) = f  ( E 0 -q  0 ), 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)

Sweet-Parker is out, E ≠  *j !

Current channel expelled,  J Magnetic energy released R BzBz v A ~ 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 × H × (500A) 2 ~ 0.8 J Electron energization ~ 500 A × 80V × 2  s ~ 0.8 J Ion flows: ~ 24 eV × 2  m -3 ×0.06m 3 ~ 0.48 J Strong energizations of the ions

Electrostatic (and magnetic) fluctuations observed during reconnection events Loop voltage (V) Fluctuation > 10 MHz (au) Spectrogram f (MHz) 0 1 t (ms) [Mar 22 shot 405, HPF 80kHz, scope B/W 150 MHz] f LH ~ 10 MHz f pi ~ 30 MHz (off scale) f pe ~ 10 GHz f ce ~ 1 GHz Plasma 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 B cusp, B guide, T e, N e, E rec. Spans collisional to collisionless regimes: e = 0.1 – 10 3 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