In situ observations of magnetic reconnection in solar system plasma

Alessandro Retin, F. Sahraoui, G. BelmontLaboratoire de Physique des Plasmas - CNRS, St.-Maur-des-Fosss, France

A. Vaivads, Y. KhotyaintsevSwedish Institute of Space Physics, Uppsala, Sweden

R. Nakamura, B. Zieger, W. BaumjohannSpace Research Institute, Graz, Austria

D. Sundkvist, S. Bale, F. S. MozerSpace Sciences Laboratory, University of California, Berkeley, USA

M. Fujimoto, K. TanakaISAS-JAXA, Sagamihara, Japan

In situ observations of magnetic reconnection in solar system plasma

Vlasov-Maxwell kinetics: theory, simulations and observations in space plasmasWolfgang Pauli Institute Wien29.03.2011

OutlineMagnetic reconnection

In situ spacecraft observations of reconnectionin near-Earth space

Some key open issues:microphysicsparticle accelerationreconnection & turbulence

Current & future spacecraft data relevant for reconnection

Summary

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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):

[ adopted from Paschmann, Nature, 2006]d_MHD ( >> i) ~ 103 kmd_ion ( ~ i ) ~ 50 kmd_electron ( ~ e) ~ 1 kmdD d L D

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

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Near-Earth space as laboratory*LABNEAR-EARTHSUNASTRODirect measur. of E & B yesyes (high res)nonoDirect measur. of f(v)noyes (high res)nonoImagingnonoyes (high res)yesBoundary conditionsartificialnaturalnaturalnaturalRepeatabilityyesnononoNumber of objectsa fewoneonemany

[Vaivads et al., Plasma Phys. Contr. Fus., 2009]

Solar system plasma (very often) are:fully ionized mainly H+, e-not relativistic (Va

Collisonless reconnection in near-Earth spacesolar 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: Retin et al., Nature Physics, 2007; Phan et al., PRL, 2007KH- vortexes: Nykiri et al., Ann. Geophsy., 2006; Hasegawa et al.,, JGR, 2009magnetotail: Hones, GRL, 1984; Nagai, JGR, 2001; ieroset, Nature, 2001; Runov et al., GRL, 2002

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ESA-Cluster spacecraft*first 4 spacecraft mission distinguish temporal/spatial variationsmeasurement of 3D quantities: J=(1/0) xB,B = 0, EJ, etc.tetrahedrical configuration with changeable spacecraft separation 100-10000 km -> measurements at different scales

4 sets of 11 identical instruments to measure:DC magnetic fieldDC electric fieldwavesthermal particle distribution functions suprathermal particle distribution functions

DC magnetometer[http://sci.esa.int/sciencee/www/area/index.cfm?fareaid=8]

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In situ spacecraft observations of reconnection*[adopted from Baumjohann & Treumann, 1996][Phan et al., Ann.Geophys., 2004][Vaivadset al., PRL., 2004]Alfvenic jetsCurrent sheetCurrent sheetHall physics L ~ 107 km >> i

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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

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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?...

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[Mozer et al., PRL, 2002]Textbook example (rare !):antiparallel reconnectionHall fieldsReconnection electric fieldReconnection rate ~ 0.1also Cluster [Runov, et al., GRL, 2002; Vaivads et al., PRL, 2004Diffusion regions

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!

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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 C1 as expected. Jet reversal indicates vicinity to the X-line.

rec. rate = /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

MP crossing - fluid scales MSHMSP[Retin et al., in preparation, 2011]

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* 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 ?

MP crossing sub-ion scales MSPMSH

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[Retin et al., GRL, 2006]

strong activity also away from the X-line ion acceleration (jet) and non-thermal electron acceleration in the separatrix region

Separatrix regionalso [Wygant et al., JGR, 2005; Cattell. et al., JGR, 2005; Khotyaintsev et al., PRL, 2006]

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Particle accelerationIs 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.)?...

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

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Electron acceleration in thin CSMagnetotail reconnectionAlfvnic plasma outflowsHighest flux increase associated with thin CS embedded in outflow

[Retin et al., JGR, 2008]Electron acceleration in thin current sheet

Electron acceleration in thin CSdirect 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 ! Acceleration mechanisms

The flow (jet) braking region**flow braking regionX-line/ microphysics (sub-ion scales) [Nakamura2009, Retin2010 submitted, Zieger2011 in preparation]

/ particle acceleration [Asano2010, Retin2010, Zieger2011]

[adopted from Birn2005]

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Cluster multi-scale orbits in 2007**[email protected] 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!

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Electron acceleration in the flow braking region**[email protected]/ 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

Vx=Ey/BzH+kBTikBTeenergetic e-e-wavesflowmag

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**[email protected]/ thickness from two-point measurements C3-C4/Hall physics Ex~(JyxBz)/Ne /strong Ey and lower-hybrid waves/electron acceleration up to ~400 keV

Dx~70 km ~ several re Acceleration in thin current layers

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Reconnection & turbulenceLarge-scale laminar vs small-scale turbulent current sheets*[Phan et al., Nature, 2006]L ~ 3 106 km ~ Ls Coronal loop observed by NASA/TRACE (UV ~106 K)L ~105 km ~ Ls [Dmitruk & Matthaeus, Phys. Plasmas, 2006]L

Reconnection & turbulenceSmall-scale current sheets in turbulence[Matthaeus & Lamkin, Phys. Fluids,1986; Dmitruk & Matthaeus, Phys; Plasmas, 2006; Servidio et al., Phys. Plasmas, 2010]

Turbulent current sheet[Lazarian & Vishniac, ApJ, 1999; Loureiro et al., MNRAS, 2009]

Turbulence/waves in laminar current sheet[Belmont & Rezeau, JGR, 2001; Bale et al;, GRL, 2002; Vaivadset al., GRL, 2004; Khotyaintsev et al., Ann. Geophys., 2004;Retin et al., GRL, 2006; Eastwood et al.; PRL, 2009; Huang etal., JGR, 2010]

Dd

*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? ...

Reconnection & turbulence

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In situ evidence of reconnection in turbulent plasma (I)cartoon of small-scale current sheets formation in turbulent plasmareconnecting current sheets[Retin et al., Nature Physics, 2007]further evidence in fast SW [Gosling et al., ApJLett, 2007]

dN/N ~ 1dB/N ~ 1Energetic ions~ d

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In situ evidence of reconnection in turbulent plasma (II)[Retin et al., Nature Physics, 2007]further evidence in fast SW [Gosling et al., ApJLett, 2007]

4 spacecraft crucial to determine the thickness d~li of the current sheetcurrent sheetenergy dissipationelectron heatingplasma accelerationrate ~ 0.1 (fast)LH turbulencetopology changeHall field

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Turbulence propertiesAlfvenic turbulence close to -5/3 (inertial range)

Intermittency at scales of a few i 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

[Sundkvist et al., PRL, 2007]

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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

Radio galaxy [adopted fromhttp://www.ece.unm.edu/~plasma/Space/jets.htm][Mann et al., A&A, 2009]

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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 spaceGoal: 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

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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 scalesStructure of separatix regiuon

Particle acceleration:Electron acceleration mechanisms in thin current sheetElectron 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

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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 scalesPIC/Vlasov+ hybrid: particle accelerationPIC/Vlasov + hybrid + MHD: turbulent reconnection

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Define multi step**We consider first the case of acceleration during reconnection in laminar single current sheet.

Steady reconnection in such configuration difficult to accelerate particles. For fast reconnection R=0.1 small reconnection fields (e.g. ~ 1mV/m in the magnetotail) thus unrealistic length of acceleration region/X-line. To get observed energies either stronger fields or particle need to spend more time in acceleration region (e.g. trapping). This is more likelyduring unsteady reconnection when (1) stronger electric fields can be produced (2) transient structures such as magnetic islands can form.

Early observations of energetic particles e.g. during substorms in the magnetotail showed explosive burst of energetic particles from reconnection regions indicating around onset time when reconnection rapidly starts in thin CS around the X-line. This explosive behavior also typical of solar flares.

Most likely strongest acceleration in TCS during unsteady reconnection. Here three examples (among many) of electron acceleration in TCS:Direct acceleration by reconnection electric fieldsFermi acceleration in contracting magnetic islandsNon-adiabatic acceleration at magnetic flux pile-up in the outflow region (gradB + curvB+wave scattering) Top: acceleration region geometryBottom: particle spectra

Of course further acceleration can occurr away from the X-line in regions of strong inductive fields where the magnetic field geometry changes rapidly t. Ex. dipolarization region. See presentation on Friday.

Define multi step*Define multi step*Virtual spacecraft*1 AU = 150 * 10(6) km

L sun = 7*10(5) km

L heliosphere ~ 100 AU ~ 1.5*10(10) km

L current sheet ~ 3*10(6) km

The heating of the solar chromosphere and corona is a long-standing puzzle in solar physics. Hinode observations show the ubiquitous presence of chromospheric anemone jets outside sunspots in active regions. They are typically 3 to 7 arc seconds = 2000 to 5000 kilometers long and 0.2 to 0.4 arc second = 150 to 300 kilometers wide, and their velocity is 10 to 20 kilometers per second. These small jets have an inverted Y-shape, similar to the shape of x-ray anemone jets in the corona. These features imply that magnetic reconnection similar to that in the corona is occurring at a much smaller spatial scale throughout the chromosphere and suggest that the heating of the solar chromosphere and corona may be related to small-scale ubiquitous reconnection. *Dmitruk: decaying three-dimensional compressible MHD with Hall termServidio, Matthaues: decaying, incompressible, two-dimensional magnetohydrodynamics.*Dmitruk: decaying three-dimensional compressible MHD with Hall termServidio, Matthaues: decaying, incompressible, two-dimensional magnetohydrodynamics.*Dmitruk: decaying three-dimensional compressible MHD with Hall termServidio, Matthaues: decaying, incompressible, two-dimensional magnetohydrodynamics.*

The demonstrated association ofcurrent sheets with intermittency and larger scale structuresleads us to denote this as a coherent dissipationmechanism, representing nonlocal (in wave-number space)interactions of different scales. This is in contrast to classicaldissipation scenarios manifested by, e.g., Landau orcyclotron damping.

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The demonstrated association ofcurrent sheets with intermittency and larger scale structuresleads us to denote this as a coherent dissipationmechanism, representing nonlocal (in wave-number space)interactions of different scales. This is in contrast to classicaldissipation scenarios manifested by, e.g., Landau orcyclotron damping.

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In situ observations of magnetic reconnection in solar system plasma

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