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In situ observations of magnetic reconnection in solar system plasma

In situ observations of magnetic reconnection in solar system plasma. Alessandro Retinò , F. Sahraoui, G. Belmont Laboratoire de Physique des Plasmas - CNRS, St.-Maur-des-Fossés, France A. Vaivads, Y. Khotyaintsev Swedish Institute of Space Physics, Uppsala, Sweden

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In situ observations of magnetic reconnection in solar system plasma

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  1. In situ observations of magnetic reconnection in solar system plasma Alessandro Retinò, F. Sahraoui, G. Belmont Laboratoire de Physique des Plasmas - CNRS, St.-Maur-des-Fossés, France A. Vaivads, Y. Khotyaintsev Swedish Institute of Space Physics, Uppsala, Sweden R. Nakamura, B. Zieger, W. Baumjohann Space Research Institute, Graz, Austria D. Sundkvist, S. Bale, F. S. Mozer Space Sciences Laboratory, University of California, Berkeley, USA M. Fujimoto, K. Tanaka ISAS-JAXA, Sagamihara, Japan Vlasov-Maxwell kinetics: theory, simulations and observations in space plasmas Wolfgang Pauli Institute– Wien 29.03.2011

  2. Outline • Magnetic reconnection • In situ spacecraft observations of reconnectionin near-Earth space • Some key open issues: • microphysics • particle acceleration • reconnection & turbulence • Current & future spacecraft data relevant for reconnection • Summary alessandro.retino@lpp.polytechnique.fr

  3. Magnetic reconnection • Violation of the frozen-in condition in thin boundaries (current sheets) • Effects: • magnetic topology change (E||) • plasma transport across boundaries • plasma acceleration (alfvenic) • plasma heating • particle acceleration (non-thermal) • Importance of scales (collisionless): • E' = E+u x B = 0 • E||=0 D  d  L  D d * anomalous conductivity MHD electron pressure electron inertia Hall d_MHD ( >> i) ~ 103 km d_ion ( ~i ) ~ 50 km d_electron ( ~e) ~ 1 km • E' = E+u x B =J/ • E||≠0 [ adopted from Paschmann, Nature, 2006]

  4. Reconnection in the plasma Universe X X X X X L ~ 107 m Laboratory plasma [Intrator et al., Nature Physics, 2009] Near-Earth space [Paschmann, 2008] L ~ 10-2 m Solar corona [Yokoyama et. al., ApJ Lett., 2001] Radio galaxy lobes [Kronberg et al., ApJ, 2004] L ~ 108 m L ~ 1016 m (?)

  5. Near-Earth space as laboratory • LABNEAR-EARTH SUN ASTRO • Direct measur. of E & B yesyes (high res)nono • Direct measur. of f(v)noyes (high res)nono • Imagingnonoyes (high res)yes • Boundary conditionsartificialnaturalnaturalnatural • Repeatabilityyesnonono • Number of objects a fewoneonemany • Solar system plasma (very often) are: • fully ionized • mainly H+, e- • not relativistic (Va<<c) • collisionless [Vaivads et al., Plasma Phys. Contr. Fus., 2009]

  6. Collisonless reconnection in near-Earth space X X X X X solar wind: Gosling et al., JGR,2005; Phan et al., Nature, 2006; magnetopause: Paschmann et al., Nature, 1979; Sonnerup et al, JGR, 1981; Mozer et al., PRL, 2002; Vaivads et al., PRL, 2004; magnetosheath: Retinò et al., Nature Physics, 2007; Phan et al., PRL, 2007 KH- vortexes: Nykiri et al., Ann. Geophsy., 2006; Hasegawa et al.,, JGR, 2009 magnetotail: Hones, GRL, 1984; Nagai, JGR, 2001; Øieroset, Nature, 2001; Runov et al., GRL, 2002

  7. ESA-Cluster spacecraft • first 4 spacecraft mission • distinguish temporal/spatial variations • measurement of 3D quantities: J=(1/μ0) xB, • B = 0, EJ, etc. • tetrahedrical configuration with changeable spacecraft separation 100-10000 km -> measurements at different scales [http://sci.esa.int/sciencee/www/area/index.cfm?fareaid=8] • 4 sets of 11 identical instruments to measure: • DC magnetic field • DC electric field • waves • thermal particle distribution functions • suprathermal particle distribution functions DC magnetometer

  8. In situ spacecraft observations of reconnection Alfvenic jets Current sheet  L ~ 107 km >> ρi [Phan et al., Ann.Geophys., 2004] Current sheet Hall physics [adopted from Baumjohann & Treumann, 1996] [Vaivadset al., PRL., 2004]

  9. Some key open issues(to be addressed by in situ obs – simulations synergy) • Microphysics i.e. physics at ion scales and below • Particle acceleration i.e. ion & electron acceleration at non-thermal energies • Relationship between reconnection and turbulence

  10. Microphysics • What is the structure and dynamics of the diffusion regions (ion & electron)? • How does reconnection start in the electron diffusion region (onset)? • Is (collisionless) reconnection always fast? • How ions and electrons are heated/accelerated? • What is the role of the separatrix region? • ...

  11. Diffusion regions • Textbook example (rare !): • antiparallel reconnection • Hall fields • Reconnection electric field • Reconnection rate ~ 0.1 also Cluster [Runov, et al., GRL, 2002; Vaivads et al., PRL, 2004 [Mozer et al., PRL, 2002]

  12. Cluster multi-scale orbits in 2008 • C1, C2, C3/C4 at fluid/MHD scales ~ 1000 km • C3, C4 at sub-ion scales ~ 20 km • subsolar magnetopause crossed ~ 10 Re • important for MMS preparation!

  13. MP crossing - fluid scales MSP MSH • guide field + asymmetric reconnection • reconnection jets in the MP/BL VL~ 200 km/s ~ 2*VA [Nmsh~15cc, BL,msh ~ 20 nT]. • VL <0 for C3, VL>0 for C1 as expected. Jet reversal indicates vicinity to the X-line. • rec. rate = <VN>/VA ~ 0.1 (but large errors) • electron par-perp anisotropy within MP • timing C1 – C3 not possible (too large separation) -> MP thickness? • multi-scale coupling <VN> [Retinò et al., in preparation, 2011]

  14. MP crossing – sub-ion scales • comparison of BL between C3-C4 -> MP thickness ~ 20 km ~ 10 re. MP basically standing VN,MP ~ 1 km/s ~ VC3,C4 (temporal variations = spatial variations) • thin MP stable over ~ 15s ~ many ion gyroperiods i-1 • C3, C4 at different locations within MP -> correl. EX, BL proxy of distance from center of MP • strong parallel current JM ~ 100 nA/m2 and field-aligned (parallel) heating • strong wave turbulence (not shown) • evidence of electron diffusion region ? MSH MSP

  15. Separatrix region [Retinò et al., GRL, 2006] • strong activity also away from the X-line • ion acceleration (jet) and non-thermal electron acceleration in the separatrix region also [Wygant et al., JGR, 2005; Cattell. et al., JGR, 2005; Khotyaintsev et al., PRL, 2006]

  16. Particle acceleration • Is reconnection always efficient for particle acceleration? • How are particles accelerated around the diffusion region (reconnection electric field vs multi-step acceleration)? • How are particle accelerated away from the diffusion region (dipolarization fronts, flow braking region, etc.)? • ...

  17. Non-thermal electron acceleration Acceleration at magnetic flux pile-up in outflow region [Hoshino 2001, Imada 2007] X-line acceleration [Pritchett 2006,Øieroset 2002, Retinò 2008] Acceleration in contracting magnetic islands [Drake 2006, Chen 2008] Strongest acceleration during unsteady reconnection in thin current sheets

  18. Electron acceleration in thin current sheet Electron acceleration in thin CS • Magnetotail reconnection • Alfvénic plasma outflows • Highest flux increase associated with thin CS embedded in outflow [Retinò et al., JGR, 2008]

  19. Acceleration mechanisms Electron acceleration in thin CS • direct X-line acceleration by Ey ~ 7 mV/m (unsteady reconnection) • further acceleration within flux rope by betatron + pitch-angle scattering (’gyrorelaxation’) sub-spin time resolution measurements crucial !

  20. The flow (jet) braking region flow braking region X-line [adopted from Birn2005] / microphysics (sub-ion scales) [Nakamura2009, Retinò2010 submitted, Zieger2011 in preparation] / particle acceleration [Asano2010, Retinò2010, Zieger2011]

  21. Cluster multi-scale orbits in 2007 • C1, C2, C3/C4 at fluid/MHD scales ~ 1000 km • C3, C4 sub-ion scales ~ 20 km • near-Earth plasma sheet crossed ~ 10 RE • important for MMS preparation! alessandro.retino@lpp.polytechnique.fr

  22. Electron acceleration in the flow braking region kBTi H+ • / flow braking from two-point measurements C1-C4 (MHD/fluid scale) • /large-amplitude magnetic field fluctuations • /strong lower hybrid and whistler waves • /supra-thermal particle acceleration • /multi-scale coupling energetic e- kBTe e- waves mag Vx=Ey/Bz flow alessandro.retino@lpp.polytechnique.fr

  23. Acceleration in thin current layers Dx~70 km ~ several re • / thickness from two-point measurements C3-C4 • /Hall physics Ex~(JyxBz)/Ne • /strong Ey and lower-hybrid waves • /electron acceleration up to ~400 keV alessandro.retino@lpp.polytechnique.fr

  24. Reconnection & turbulenceLarge-scale laminar vs small-scale turbulent current sheets L << Ls L ~ 3 ·106 km ~ Ls L Ls |B| Hall MHD [Phan et al., Nature, 2006] [Dmitruk & Matthaeus, Phys. Plasmas, 2006] L ~105 km ~ Ls Ca II image from Hinode - SOT L ~ 103 km << Ls Coronal loop observed by NASA/TRACE (UV ~106 K) [Shibata et al., Science, 2007]

  25. Reconnection & turbulence • Small-scale current sheets in turbulence • [Matthaeus & Lamkin, Phys. Fluids,1986; Dmitruk & • Matthaeus, Phys; Plasmas, 2006; Servidio et al., Phys. • Plasmas, 2010] D d • Turbulent current sheet • [Lazarian & Vishniac, ApJ, 1999; Loureiro et al., MNRAS, 2009]  << D • Turbulence/waves in laminar current sheet • [Belmont & Rezeau, JGR, 2001; Bale et al;, GRL, 2002; Vaivads • et al., GRL, 2004; Khotyaintsev et al., Ann. Geophys., 2004; • Retinò et al., GRL, 2006; Eastwood et al.; PRL, 2009; Huang et • al., JGR, 2010]

  26. Reconnection & turbulence • How do small-scale current sheets form in turbulence ? • Is reconnection occurring in such current sheets ? • Is reconnection in turbulent plasma faster than laminar reconnection ? (reconnection rate) • What is the role of small-scale reconnecting current sheets for energy dissipation in turbulent plasma ? • Is reconnection in turbulent plasma efficient for accelerating particles to non-thermal energies? • ...

  27. In situ evidence of reconnection in turbulent plasma (I) Energetic ions quasi- quasi-|| dN/N ~ 1 ~ d dB/N ~ 1 cartoon of small-scale current sheets formation in turbulent plasma reconnecting current sheets [Retinò et al., Nature Physics, 2007] further evidence in fast SW [Gosling et al., ApJLett, 2007]

  28. In situ evidence of reconnection in turbulent plasma (II) current sheet Hall field LH turbulence rate ~ 0.1 (fast) topology change plasma acceleration electron heating energy dissipation 4 spacecraft crucial to determine the thickness d~li of the current sheet [Retinò et al., Nature Physics, 2007] further evidence in fast SW [Gosling et al., ApJLett, 2007]

  29. Turbulence properties Intermittency Gaussian dissip/disp. range B • Alfvenic turbulence close to -5/3 • (inertial range) • Intermittency at scales of a few ρi and smaller ( close to dissip./disp. range) -> presence of coherent structures • dissipation in current sheets with d~ li comparable to wave damping around wci -> turbulent reconnection competing mechanism for energy dissipation at li scales inertial range E' alfvenic turbulence i i [Sundkvist et al., PRL, 2007]

  30. Possible applications of results from in situ observations (with caution!) • Sawtooth oscillations in tokamaks • Coronal heating • Particle acceleration in solar flares • Dissipation in accretion disks • Cosmic rays acceleration [Mann et al., A&A, 2009] Radio galaxy [adopted from http://www.ece.unm.edu/~plasma/Space/jets.htm]

  31. Current & future spacecraft data relevant for reconnection (and with LPP involvement) ESA/Cluster [http://sci.esa.int/cluster]: 2000-2012(2014) -- near-Earth space NASA/Themis [http://themis.ssl.berkeley.edu]: 2007 -- near-Earth space NASA/MMS [http://mms.gsfc.nasa.gov]: 2014 -- near-Earth space Goal: the physics of reconnection at electron scales (also turbulence, particle acceleration) ESA/SolarOrbiter [http://sci.esa.int/solarorbiter]: 2017 -- near-Sun corona (62 Rs). Goals: solar wind acceleration, coronal heating, production of energetic particles (turbulence, reconnection) ESA/SolarProbePlus [http://solarprobe.gsfc.nasa.gov]: 2018 -- near-Sun corona (8.5 Rs). Similar goals to SolarOrbiter

  32. Summary (I) • Reconnection universal process responsible for mayor plasma transport, plasma acceleration / heating and non-thermal particle acceleration • Near-Earth space excellent laboratory to study the physics of reconnection through in situ measurements (Cluster first multi-point) • Microphysics of reconnection: • Observations at sub-ion scales • Structure of separatix regiuon • Particle acceleration: • Electron acceleration mechanisms in thin current sheet • Electron acceleration mechanisms in the flow braking region • Reconnection and turbulence: • Evidence of reconnection in turbulent plasma in small-scale current sheets. • Turbulent reconnection can be efficient mechanism for energy dissipation

  33. Summary (II) • Possible applications of results from in situ obs: sawtooth oscillations in tokamaks, coronal heating, particle acceleration in flares, dissipation in accretion disks, cosmic ray acceleration etc. • Future missions will (hopefully) improve our understanding of reconnection at electron scales, particle acceleration and turbulent reconnection. Current missions (Cluster, Themis) very important for preparation! • Synergy between in situ ibs – simulations very important: • PIC/Vlasov: electron scales • PIC/Vlasov+ hybrid: particle acceleration • PIC/Vlasov + hybrid + MHD: turbulent reconnection

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