Magnetic Reconnection during Turbulence and the Role it
Plays in Dissipation and HeatingMichael Shay
Bartol Research InstituteUniversity of Delaware
C. Haggerty, T. Parashar, W. Matthaeus, R. BandyopadyayT. D. Phan, J. F. Drake, Y. Yang, M. Wan, S. Servidio,
P. WuM. A. Shay, C. C. Haggerty, W. H. Matthaeus, T. N. Parashar, M. Wan, and P. Wu, Turbulent heating due to magnetic reconnection, Physics of Plasmas, 25, 012304 (2018);
Haggerty, C. C., T. N. Parashar, W. H. Matthaeus, M. A. Shay, Y. Yang, M. Wan, P. Wu, and S. Servidio, Exploring the statistics of magnetic reconnection X-points in kinetic particle-in-cell turbulence, Physics of Plasmas, 24, 102308, 2017, doi:10.1063/1.5001722.
Motivation• Focus: Turbulence
– Not reconnection generated turbulence• Significant advances recently on the nature of plasma heating
during magnetic reconnection– e.g., Phan et al., 2013, 2104; Yamada et al., 2014, Shay et al., 2014;
Haggerty et al., 2015; Wang et al., and many more• Kinetic simulations of turbulence: some inertial range to electron
scales– e.g., Howes et al., Tenbarge et al., Karimabadi et al., Parashar et al,
Gary et al., and many more. • Can we apply our understanding of “simple” magnetic
reconnection to turbulent heating?– Short Answer: Yes …. But …..
Overview• Background• Laminar Reconnection Studies
– Heating in Reconnection Exhausts• Framework: Apply Heating Predictions to
Turbulence• Kinetic PIC Turbulence Simulations
– Test Framework• Statistics of Reconnection: Kinetic PIC
Simulations
Overview• Background• Laminar Reconnection Studies
– Heating in Reconnection Exhausts• Framework: Apply Heating Predictions to
Turbulence• Kinetic PIC Turbulence Simulations
– Test Framework• Statistics of Reconnection: Kinetic PIC
Simulations
Solar Wind Turbulence
Notice the Comet!
“Powerlaws everywhere”!
• Solar wind
• Corona
• Diffuse ISM
• Geophysical flows
Interstellar medium: Armstrong et al
SW at 2.8 AU: Matthaeus and Goldstein
Broadband self-similar spectra are a signature of cascade
Coronal scintillation results (Harmon and Coles)Tidal channel: Grant, Stewart and Moilliet
Heating by turbulence cascade
energy containing
energy input
inertial dissipation
heati
ng
cascade
En
er
gy s
pectr
um
E(k
)
Log(wavenumber)
• heat the plasma, • increasing the pressure gradient • adding momentum ! producing the solar wind
…in corona, turbulence can:
Where the heating occurs is important!
Plasma Heating - Magnetic Dissipation?• Something is heating the
solar wind
!8
• Something is heating the solar corona
Wang et al., JGR, 106, 29401, 2001
Model of Photosphere/Corona Transition “Physics of the Solar Corona,”
Aschwanden, 2005.
Physical Dissipation Mechanisms for Kinetic Turbulence
Three mechanisms have been proposed:
(1) Collisionless Wave-Particle Interactions (Landau damping) (Leamon et al., 1998, 1999, 2000; Quateart & Gruzinov, 1999; Howes et al.
2008; Schekochihin et al. 2009; TenBarge & Howes 2012)
(3) Dissipation in Current Sheets (Dmitruk et al. 2004; Markovskii & Vasquez 2011; Matthaeus & Velli 2011;
Osman et al. 2012; Servidio 2011)
(2) Stochastic Heating(Johnson & Cheng, 2001; Chen et al. 2001; White et al., 2002; Voitenko &
Goosens, 2004; Bourouaine et al., 2008; Chandran et al. 2010; Chandran 2010)
Key Goal:-To compare and contrast the different turbulence theories -To identify observational and numerical tests to distinguish these
distinct models
From SHINE conference, 2014
Howes/Shay Session Description
Phan et al., Nature, 2018• Reconnection in Turbulent Magnetosheath
– “Electron-Only” Reconnection
BLMN
Vi LMN
ExB/B2
ELMN
(mV/m)
j.(E+VexB) (nW/m3)
E||
Ve LMN
jLMN(µA/m2)
MMS 1 and MMS 3 on opposite sides of the X-line: smoking gun evidence for reconnection
veL
MMS 1
veM
jL jM
EN EM
45 ms
ΔVeL < 0
EN > 0
Δ(ExB/B2)L
veL veM ΔVeL > 0Δ(ExB/B2)L
EN < 0
MMS 3 45 ms
electron jet
MMS 1
MMS 3EN
EN
Magnetic-to-electron energy conversion
Overview• Background• Laminar Reconnection Studies
– Heating in Reconnection Exhausts• Framework: Apply Heating Predictions to
Turbulence• Kinetic PIC Turbulence Simulations
– Test Framework• Statistics of Reconnection: Kinetic PIC
Simulations
Vx
Character of Reconnection Heating• Heating Tends to Occur as
beams– Especially: Ion Heating
Gosling et al., 2005
f
v||
Lottermoser et al., 1998
Simulations
Solar Wind Observations
“Simple” Problem: Heating in Reconnection Exhausts
• Focus on Understanding Heating in Reconnection Exhausts
• Heating Definition:
– Counter-streaming beams are considered “heating”.
• Systematic Kinetic PIC Simulations
T =1
n
Zd3vf(x, v)(v � u)(v � u)
T =1
3Tr[T]
Energy Budget
δ
D
Vin
Vin
B
B
VoutVout
• Magnetic Energy In: • Flow Energy, Thermal Energy, Heat Flux out
B2
4⇡VinD =
1
2minV
2out +
�
� � 1�Ten+
�
� � 1�Tin
�Vout� +Qix +Qex
Energy Budget: Heating• Energy Conservation
Divide eqn by left hand side
• 1 = αflow + αTe + αTi + αQi + αQe
• αT = % of released energy that heats a species.
• Important Questions – Is αT a constant? What does it depend on? – What is the value of αT?
– What is 𝛾/(𝛾-1)? (5/2 for adiabatic) Review in: Shay et al., 2014
↵T ⇡ �
� � 1
�T
B2/(4⇡n)
B2
4⇡VinD =
1
2minoutV
3out +
�
� � 1�Tenout Vout +
�
� � 1�Tinout Vout
�� + Qix + Qex
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Laminar Reconnection Simulations• Reconnection heating depends
strongly on parameters upstream of x-line.
– cAr: Alfven speed based on reconnection field
– Br: reconnection field– B: Total Field
• MTi, MTe are constants• ΔTi consistent with
Drake et al., 2009• Relative heating is:
mi c2Ar
B2r
B2
ΔTi
mi c2Ar
Br
B
ΔTe
Dataset limited to:
Bguide > 0.2Te/Ti < 1.25βi < 2
�Ti = MTi c2Ar
B2r
B2
�Te = MTe c2Ar
Br
B
�Ti
�Te/ Br
B
Question• Can we take this knowledge about laminar
reconnection and apply it to reconnection during turbulence?
Overview• Background• Laminar Reconnection Studies
– Heating in Reconnection Exhausts• Framework: Apply Heating Predictions to
Turbulence• Kinetic PIC Turbulence Simulations
– Test Framework• Statistics of Reconnection: Kinetic PIC
Simulations
Heating in Turbulence Due to Reconnection?
• Multifaceted problem – Magnitude and Character of Heating
due to Reconnection?• What parameters does the heating
depend on?– Properties of Magnetic Reconnection
in Turbulence?• How many x-lines? How many
reconnecting x-lines?– Relative role of heating due to
magnetic reconnection versus other sources of heating
• Kinetic PIC Simulation Study– Can we apply our understanding of
“simple” magnetic reconnection to turbulent heating?
– What are the statistics of X-lines in kinetic turbulence simulations?
Haggerty el al., 2017Kinetic PIC Turbulence Simulation
Magnetic Flux Contours with X-llines
Flux Bundles Reconnecting• Energy released into ions:
Single Flux Bundle:
• Sum Over All Bundles:
CAr
`>
`<
X
Y
Servidio, 2010
Magnetic Flux Contours
" =MT
2
X
x-line i
`<i `>i B2ir
B2ir
B2
" =
MT
2
X
x-line i
`<i `>i
!B2
irB2
ir
B2
"⇥ = 2⇡�T `< `>nr
"⇥ =MT
2`< `> B2
rB2
r
B2
Determine Bir?• Assume mean field is constant and B0 >> Bir • First estimate: Width of reconnection sites typically ~ di
– What are magnetic fluctuations at scale size di?• Assume δZ at di scales like reconnection Alfven speed: δZdi ∝ Car
• Where cA is Alfven speed based on global RMS B• 𝜏nl(di) is nonlinear time at ion inertial scale
• 𝜏c is cyclotron time based on global RMS B ≈ B0
Protons:
Electrons: "e =�Z3
di
c3A
MT
2B2
X
x-line i
`<i `>i
!= ↵3
nl ( Flux Bundle Details )
"p =�Z4
di
c4A
MT
2B2
X
x-line i
`<i `>i
!= ↵4
nl ( Flux Bundle Details )
cAr
cA=
Br
B=
�Zdi
cA
didi
=⌧ci
⌧nl(di)⌘ ↵nl
Key Points• Turbulent heating due to reconnection
estimated to be:
• Will ( Flux Bundle Details ) remain invariant as we change turbulence properties?
• Proton to electron heating scaling expected to be more accurate.
"p = ↵4nl ( Flux Bundle Details )
"e = ↵3nl ( Flux Bundle Details )
"p"e
/ ↵nl
Overview• Background• Laminar Reconnection Studies
– Heating in Reconnection Exhausts• Framework: Apply Heating Predictions to
Turbulence• Kinetic PIC Turbulence Simulations
– Test Framework• Statistics of Reconnection: Kinetic PIC
Simulations
Kinetic PIC Turbulence Simulations
• Wu et al, 2013, Parashar et al., 2016.
• 2 1/2 Dimensions• Initial uniform Bz = 5• Initial Perturbation:
Z20 ⌘ hv2i+ h B2
4⇡mini
NASA Phan et al Publicity Movie, 2018
Turbulence Simulations• Constant Mean field B0 = 5, B >> Br
5
run family βi βe Z0 B0 λc L Nx = Ny Qi/Qe τc/τnl ppg krun805.1 PAPJ15 0.08 0.08 1.1 5.0 0.445 1.28 64 0.584 0.534 200 {1,2}run805.2 PAPJ15 0.08 0.08 0.825 5.0 0.445 2.56 128 0.887 0.340 200 {1,2}run805.3 PAPJ15 0.08 0.08 0.737 5.0 0.445 5.12 256 0.435 0.260 200 {1,2}run805.4 PAPJ15 0.08 0.08 0.713 5.0 0.445 10.24 512 0.331 0.209 200 {1,2}run805.5 PAPJ15 0.08 0.08 0.707 5.0 0.445 20.48 1024 0.343 0.169 200 {1,2}run809.1 OTVdbB 0.08 0.08 0.718 5.0 3.820 20.48 1024 0.551 0.169 200 {1,2}run810.1 OTVdbB 0.08 0.08 1.075 5.0 3.928 20.48 1024 0.588 0.251 200 {1,2}run811.1 OTVdbB 0.08 0.08 1.433 5.0 4.286 20.48 1024 0.754 0.325 200 {1,2}run812.1 OTVdbB 0.08 0.08 1.790 5.0 4.608 20.48 1024 0.945 0.397 200 {1,2}Turb808 k13 0.25 0.25 1.0 5.0 0.349 25.6 2048 0.404 0.173 400 {1,3}Turb812 k13 0.25 0.25 2.5 5.0 0.871 25.6 2048 0.542 0.404 400 {1,3}Turb813 k13 0.25 0.25 4.0 5.0 1.394 25.6 2048 0.857 0.606 400 {1,3}Turb814 k24lb 0.25 0.25 2.5 5.0 0.868 25.6 2048 0.697 0.419 400 {2,4}Turb815 k24lb 0.25 0.25 4.0 5.0 1.389 25.6 2048 1.159 0.646 400 {2,4}Turb816 k24sb 0.10 0.10 2.5 5.0 0.868 25.6 2048 0.546 0.427 400 {2,4}Turb817 k24sb 0.10 0.10 4.0 5.0 1.389 25.6 2048 1.010 0.664 400 {2,4}
TABLE 1Properties of simulation runs. All simulations employ P3D particle-in-cell code in 2.5D (3 components for vectors; 2 dimensional grid)periodic boxes of lengths described in the L column and grid described in the Nx = Ny column. The table does not list the runs from Wu
et al. (2013). Listed are proton beta βi, electron beta βe, turbulence amplitude Z0, out of plane unfirm magnetic field B0, correlationscale λc, box size L, grid points in plane Nx = Ny , ratio of average ion/electron heating rates Qi/Qe, ratio of proton cyclotron time to
nonlinear time at di ion inertial scale τc/τnl, number of particles per grid point ppg and wavenumber band of initial conditions. Alllengths are in di. The b and v fluctuations in the initial conditions were excited for wave-numbers having the values given in the k column
and with a given initial spectrum. The time step in all the simulations was chosen to satisfy the CFL condition for the speed of light.
wave-numbers. The energy then cascades to fill in the complete wave-number range available and produce turbulence.Typical parameters for these runs (except for Wu et al. (2013) runs) are given in Table 1.
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Determining Nonlinear Time• Estimate of 𝜏nl(di) based on von Karman-
Kolmogorov phenomenology
– λ is correlation or energy containing scale• Is this estimate applicable to our system?
⌧nl(`) =`
�Z`= ⌧nl
✓`
�
◆2/3
�Z` = Z
✓`
�
◆1/3
Turbulence Simulations: Scaling of Heating
"p"e
/ ↵nl
Approximate Best Fit Not Consistent"p / ↵3
nl "e / ↵2nl
Ratio of Heating Matches Well
Conclusions: Heating• Turbulence Simulations:
• Theory Predictions:
• Why the difference?• Is ΔB at di scale best measure of magnetic fields upstream of
current sheets?• 𝜏nl(di) determined ignoring intermittency. Justified?• Are the number of x-lines changing with changing
parameters?• Filling factor of reconnection exhausts?
• εp/εe matches reconnection prediction quite well. – Even if some details of scaling of reconnection parameters wrong,
taking the ratio removes the discrepancy.
"p"e
/ ↵nl "p / ↵3nl "e / ↵2
nl
"p"e
/ ↵nl "p / ↵4nl "e / ↵3
nl