alessandro retinò, f. sahraoui, g. belmont laboratoire de physique des plasmas - cnrs,...
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Alessandro Retinò, F. Sahraoui, G. BelmontLaboratoire de Physique des Plasmas - CNRS, St.-Maur-des-Fossés, 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 plasmas
Wolfgang Pauli Institute– Wien
29.03.2011
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
18 avril 2023 [email protected] 2
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 km
d_ion ( ~ i ) ~ 50 km
d_electron ( ~ e) ~ 1 km
Hall electron
pressure
electron inertia
*MHD anomalous
conductivity
E' = E+u x B = 0
E||=0
E' = E+u x B =J/
E||≠0
d
D d L D
Reconnection in the plasma Universe
Laboratory 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 m
L ~ 107 m
L ~ 108 m L ~ 1016 m (?)
Near-Earth space as laboratory
5
LAB NEAR-EARTH SUNASTRO
Direct measur. of E & B yes yes (high res) no no
Direct measur. of f(v) no yes (high res) no no
Imaging no no yes (high res) yes
Boundary conditions artificial natural natural natural
Repeatability yes no no no
Number of objects a few one onemany
[Vaivads et al., Plasma Phys. Contr. Fus., 2009]
Solar system plasma (very often) are:
fully ionized
mainly H+, e-
not relativistic (Va<<c)
collisionless
Collisonless reconnection in near-Earth space
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, 2007KH- vortexes: Nykiri et al., Ann. Geophsy., 2006; Hasegawa et al.,, JGR, 2009magnetotail: Hones, GRL, 1984; Nagai, JGR, 2001; Øieroset, Nature, 2001; Runov et al., GRL, 2002
ESA-Cluster spacecraft
7
first 4 spacecraft mission
distinguish temporal/spatial variations
measurement of 3D quantities: J=(1/μ0) 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 field
DC electric field
waves
thermal particle distribution functions
suprathermal particle distribution functions DC magnetometer
[http://sci.esa.int/sciencee/www/area/index.cfm?fareaid=8]
In situ spacecraft observations of reconnection
8
[adopted from Baumjohann & Treumann, 1996]
[Phan et al., Ann.Geophys., 2004]
[Vaivadset al., PRL., 2004]
Alfvenic jets
Current sheet
Current sheet
Hall physics
L ~ 107 km >> ρi
Some key open issues(to be addressed by in situ obs – simulations synergy)
9
I. Microphysics i.e. physics at ion scales and below
II. Particle acceleration i.e. ion & electron acceleration at non-thermal energies
III. Relationship between reconnection and turbulence
Microphysics
10
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?
...
[Mozer et al., PRL, 2002]
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
Diffusion regions
Cluster multi-scale orbits in 2008
12
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
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
MP crossing - fluid scales
MSH
MSP
[Retinò et al., in preparation, 2011]
<VN>
14
comparison of BL between C3-C4 -> MP thickness ~ 20 km ~ 10 e. 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
MSP
MSH
[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
Separatrix region
also [Wygant et al., JGR, 2005; Cattell. et al., JGR, 2005; Khotyaintsev et al., PRL, 2006]
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.)?
...
Non-thermal electron acceleration
Acceleration in contractingmagnetic islands[Drake 2006, Chen 2008]
X-line acceleration [Pritchett 2006,Øieroset 2002, Retinò 2008]
Acceleration at magnetic flux pile-up in outflow region[Hoshino 2001, Imada 2007]
Strongest acceleration during unsteady reconnection in thin current sheets
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]
Electron acceleration in thin current sheet
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 !
Acceleration mechanisms
The flow (jet) braking region
18 avril 2023 20
flow braking region
X-line
/ microphysics (sub-ion scales) [Nakamura2009, Retinò2010 submitted, Zieger2011 in preparation]
/ particle acceleration [Asano2010, Retinò2010, Zieger2011]
[adopted from Birn2005]
Cluster multi-scale orbits in 2007
18 avril 2023 [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!
Electron acceleration in the flow braking region
18 avril 2023 [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 couplingVx=Ey/Bz
H+
kBTi
kBTe
energetic e-
e-
waves
flow
mag
18 avril 2023 [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
x~70 km ~ several e
Acceleration in thin current layers
Reconnection & turbulenceLarge-scale laminar vs small-scale turbulent current sheets
24
[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 << Ls
Ls
[Shibata et al., Science, 2007]
Ca II image from Hinode - SOT
L ~ 103 km << Ls
L
|B|Hall MHD
Reconnection & turbulence
Small-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;Retinò et al., GRL, 2006; Eastwood et al.; PRL, 2009; Huang etal., JGR, 2010]
D
d
<< D
26
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
In situ evidence of reconnection in turbulent plasma (I)
quasi-|| quasi-
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]
N/N ~ 1
B/N ~ 1
Energetic ions
~ d
In situ evidence of reconnection in turbulent plasma (II)
[Retinò et al., Nature Physics, 2007]further evidence in fast SW [Gosling et al., ApJLett, 2007]
4 spacecraft crucial to determine the thickness d~i of the current sheet
current sheet
energy dissipation
electron heating
plasma acceleration
rate ~ 0.1 (fast)
LH turbulence
topology change
Hall field
Turbulence properties
inertial range
dissip/disp. rangeB
E'
alfvenic turbulence
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~ i
comparable to wave damping around ci -> turbulent reconnection competing mechanism for energy dissipation at i
scales
Intermittency
Gaussian
ii
[Sundkvist et al., PRL, 2007]
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]
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
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
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