O7-8

Electron physics near
the X line in asymmetricmagnetic reconnection

Seiji ZENITANI
Kobe University

Hiroshi HASEGAWA
Tsugunobu NAGAI
JAXA/ISAS

Outline• Introduction• Asymmetric reconnection (2-D PIC simulation)– 1. Crescent-shaped electron velocity distribution functions (VDFs)– 2. Sheath-side anomaly– 3. Outflow anomaly• Asymmetric reconnection with a guide-field– 4. Shannon entropy for the sheath-side boundary layer• SummaryMagnetic reconnection in near-Earth space

Burch+ 2016 Space Sci. Rev.

Magnetic reconnection in near-Earth space
Electron-scale measurement with MMS

We try to understand electron-physics
Burch+ 2016 Sciencesignatures in magnetopause reconnection
by using PIC simulations
Burch+ 2016 Space Sci. Rev.

2-D particle-in-cell (PIC) simulation• Asymmetry in plasma properties• Density variation

n1 : n2 = 3 : 1• Magnetic variation

B1 : B2 = 1 : 3• Simulation parameters• mi : me = 25 : 1• Domain size: 128.0 x 25.6 [di]Magnetosphere

ZZY

MagnetosheathXXThree features near the X line
(electron diffusion region; EDR)(c) E’
Ey0 = [E + V e ⇥ B]y

1. Sphere-side
1z

X
33. Outflow region

2. Sheath-side2x

1. Sphere-side: Crescent-shaped VDFs
Our PIC simulation

MMS observation (Burch et al. 2016)(c) E’y1z
32x

See also
Hesse et al. 2014 GRL
Bessho et al. 2016 GRL
Shay et al. 2016 GRL

Crescent-shaped VDFs = meandering electrons
VDF: ensemble of particles

Orbit in the velocity spacevz
Theoryvy
Front view

Side viewxyWhy is “crescent” clear in asymmetric RX? (1/2)
High-density
meandering electrons

Front view

Meandering electrons
are hidden here

Side viewxyWhy is “crescent” clear in asymmetric RX? (1/2)
High-density
meandering electrons

Meandering electrons
are hidden here

Sheath-origin
high-density core

Sphere-origin
low-density core
Front view

Side viewxyWhy is “crescent” clear in asymmetric RX? (2/2)
High-density
meandering electrons

Meandering electrons
are hidden here

Sheath-origin
high-density core

Sphere-origin
low-density coreion

Front viewelectronxyWhy is “crescent” clear in asymmetric RX? (2/2)
High-density
meandering electronsMeandering electrons
are hidden here

Sheath-origin
high-density core

Sphere-origin
low-density core
Front view-eEzion• (1) Low-density core and(2) electric field (Ez)make the crescent much clearer

electronxy2. Sheath-side anomaly(c) E’
Eyy0 = [E + V e ⇥ B]ySphere1• In a well magnetizedplasma, we expect anelectron condition ofz
SheathE + ve ⇥ B ' 032x

<latexit sha1_base64="z3kBLFhPd6CMfoyFiUaRwNNybVE=">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</latexit>(E + v e ⇥ B)y < 0Sharp magnetic
curvature in 3D

Larger gyro radius due toweaker magnetic field

132zxSheath-side anomaly: curvature parameter(c) E’Eyy0 = [E + V e ⇥ B]ySphere

1zSheath

32x(g) Box 2 - curv. parameter

Non-adiabatic (chaotic) ←(E + v e ⇥ B)y < 0→ Adiabatic (gyration)

R c . rLrL ⌧ R c<latexit sha1_base64="bz/I9qfOl3qgu4B5/5rXSXYUk6Q=">AAADt3ichZLNTttAEMcnuC0f/SDApVIvViOkHlC0rloQN0QvHDhA2wBSElleZwkW64+unSBk7Qv0TRDPUakvwKGPgDi2VS899O+NrSpEIWvZnp35/2Z2d5YnMkgzxn7U5qxHj5/MLywuPX32/MVyfWX1KI0HyhctP5axOuFeKmQQiVYWZFKcJEp4IZfimJ9/KOLHQ6HSII4+Z5eJ6IZePwpOA9/L4HLrbt4xSdqqz7u502RmbLD/xnvmbG86WkGpQntfa7sjpT2GQV0QGxWuP47EvtZuvVHlsieNCmhQOQ7ilZpNHepRTD4NKCRBEWWwJXmU4mmTQ4wS+LqUw6dgBSYuSNMS2AFUAgoP3nN8+5i1S2+EeZEzNbSPKhKvAmnTOrthV+wn+86u2S37OzVXbnIUa7nEn49YkbjLX19++gNqOseh17QOPTeVe7BCRDM6m1mt0j3EK7NDQRdmZ6GJRVDliA3h90EX59c1nipHtY9illMDcV2e5LRcfVTyYGszK86Um/7omavooVfDCa7ouG96ns2orErNON8xd2DUV/C4c879GzZpHL1tOqzpHL5r7OyWt2+BXtFreoMT2KId2qMDamEN3+iOftFva9tyrVPrbCSdq5XMGo0N68s/dyLOxg==</latexit><latexit sha1_base64="/Lsb1ZZhTkQPFGq5YdnjFagDVyQ=">AAADvHichVLLbtNAFL2peZTyaAobJDYWUSUWKBojHmKDKtiwYFEKaSvFUeSxh9SKX5pxgiprfoA/qfojiD0LPqG7Sl1UoC44M7EXIQoZa8b3cc69M/deXiSxKhn71Vpzrl2/cXP91sbtO3fvbba37u+rfCJD0QvzJJeHPFAiiTPRK+MyEYeFFEHKE3HAx++M/2AqpIrz7HN5XIhBGoyy+EscBiVMw3ZU+TZIX474oGJd9tRsr8vs0nvDypepG2rt+olQSsWpO8dokIbWCC+Y9/qlp+WM+0HrYbvTuN1FoQnRoXrt5lstl3yKKKeQJpSSoIxKyAkFpPD1ySNGBWwDqmCTkGLrF6RpA9wJUAKIANYxzhG0fm3NoJuYyrJDZEmwJZgubbOf7IRdsO/slJ2xq6WxKhvD3OUYfz7jimK4+e3hp0uwlvM48Jq2gec2cwQphbeko5XZGtz/+NK+UNBX+7LU+jKgKvimsIdgm/oNrKWJ0bzDaBV14Nd1JZfFGiFTAFlbzdSU2/7olbeI0KvpAs90PLQ9L1dkljVmnu/bGZj1FXzMnPfvhC0K+8+6Hut6H593dt7W07dOj+gxPUEFXtEOvadd6uEOP+icftMf540TOWMnnUHXWjXnAc0tZ/oXg/bRIA==</latexit>• The region is largely filled with
non-adiabatic electrons,
whose chaotic motion isbeyond the scope of theguiding-center approximation.
Buchner & Zelenyi
1989, 1991

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r

Rc
rL

Magnetic curvature radius
Larmor radius

E + v e ⇥ B 6= 03. Outflow anomaly(c) E’
Eyy0 = [E + V e ⇥ B]y(E + v e ⇥ B)y < 01z32xAdiabatic

Nonadiabatic

Chaotic electron motion no longer
guarantees (E + Ve x B) = 0⌘<latexit sha1_base64="t7PnDyaf+umIIgyPDIgIqoD3Lew=">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</latexit>

rRcrL

Magnetic curvature radius
Larmor radiusOutflow anomaly: MMS4 observation

E + v e ⇥ B 6= 0Hwang+ 2017 GRL

Asymmetric reconnection with a guide-field• Asymmetry in plasma properties• Density variation

n1 : n2 = 3 : 1• Magnetic variation

B1 : B2 = 1 : 3• Simulation parameters

By Guide field• mi : me = 25 : 1vex

MagnetosphereZZY

MagnetosheathXX

Unmixed electron VDF
Electron VDF

vex
Vy

Vx

Sphere-origin

Vy
Sheathorigin
Vx
PIC data• On the magnetosheath-side boundary,sphere/sheath-origin electrons are separate
in the velocity space (Hesse+ 2017 PRL)

Shannon entropy of electron VDF
Electron VDF

vex
Vy

Vx

Xpi log pii

pi : probability in the
3D velocity space

Theory predicts
an increase by ΔS = 0.35

Shannon entropySummary• Asymmetric reconnection (2-D PIC simulation)– 1. Crescent-shaped electron VDFs, due to meandering electrons– 2. Sheath-side anomaly– 3. Outflow anomaly

Nonadiabatic electrons
lead to (E + Ve x B) ≠ 0• Asymmetric reconnection with a guide-field– 4. Shannon entropy for the sheath-side boundary layer
with unmixed electron populations• Reference:– Zenitani, Hasegawa, & Nagai (2017), J. Geophys. Res. Space Physics, 122,7396-7413, doi:10.1063/1.4963008

Electron VDFs in our PIC simulation• We have uploaded 70,000 ion/electron VDFs
• Click a link in our abstract: http://rish.kyoto-u.ac.jp/~zenitani/MRA/