Kinetic aspects of the ion current
layer in an outflow exhaust inmagnetic reconnection
Seiji ZENITANI
National Astronomical Observatory of Japan

S. Zenitani, I. Shinohara, T. Nagai, & T. Wada, Phys. Plasmas 20, 092120 (2013)

Outline•1. Introduction– Kinetic structure of the reconnection site

•2. Ion velocity distribution function– Composition of the VDF– Chaotic particle motion•3. Discussion– Outflow speed problem– Multiscale picture of the outflow region•4. Summary

1. Introduction

Kinetic structure of reconnection siteionelectronIon-scale structure

Electron-scale structure(E+ve xB)y?

ZX(E+vi xB)y?
X

2D PIC simulations

Dissipation region
Generalized measure[Zenitani et al. 2011 PRL]
Energy dissipation(resistive MHD)

Total energy transfer

Work by Lorentz force (Ideal MHD)(a) anti-parallel(b) guide-field (Bg=0.8B0)

zx

Dissipation regionx

2D PIC simulationsElectron-scale structure(A) Quadrupole
magnetic field(B)-By

Hrreucallnt(F) Pedestal+By(D) Dissipation regionzy(C) Electron current layerx

Zenitani et al. 2011 PoP(E) Super-Alfvénic electron jetElectron-scale structure• The electron ideal condition is violated.
(A) Quadrupole• Super-Alfvénicelectron jet.
rentrl cula)Hmagnetic field(B-By(F) Pedestal+By(D) Dissipation regionzy(C) Electron current layer(E) Super-Alfvénic electron jetx

Zenitani et al. 2011 PoPvex

Shay et al. 2007 PRL(E+VexB) ≠ 0
Karimabadi et al. 2007 GRL

Electron-scalestructure
Ion-scalestructure(E+vi xB)yZ(A) Quadrupole
magnetic field(B)-ByHalnturrelc(F) Pedestal+By(D) Dissipation regionzy(C) Electron current layerx

Zenitani et al. 2011 PoPX(E) Super-Alfvénic electron jet

HybridLottermoser et al. 1998 JGRArzner & Scholer 2001 JGRHigashimori & Hoshino 2012
Kinetic
Drake et al. 2009 JGR
Liu et al. 2011--2012 PoPElectron-scale
structure
Ion-scalestructure(E+vi xB)yZ(A) Quadrupole
magnetic field(B)-ByHalXnturrelc(F) Pedestal

HERE+By(D) Dissipation regionzy(C) Electron current layer

xZenitani et al. 2011 PoP(E) Super-Alfvénic electron jet

HybridLottermoser et al. 1998 JGRArzner & Scholer 2001 JGRHigashimori & Hoshino 2012
Kinetic
Drake et al. 2009 JGR
Liu et al. 2011--2012 PoP•Q1. Why is the ion ideal condition violated?
•Q2. Why is the ion flow sub-Alfvénic?

2. Ion velocity distributionfunction

Ion velocity distribution function(E+vi xB)y• 2D PIC simulation• mi/me=100

Z• 76.8 x 38.4 [di]• 109 particlesX• Non-Maxwellian• Non-gyrotropicViVy• Non-idealxxVExBBzVxIon velocity distribution function• (1) global Speiser ions
• (2) local Speiser ions
• (3) trapped ions

Vz

Vy

Vy

Bz

Vx
Vx

(Global-type) Speiser orbit

Movie: X-line to outflow
Energetic tail rotates clockwise

Speiser 1965 JGR

Vyx

VyVExB
Bz

Vx

Vx

(Local-type) Speiser orbit

Zx
VExB
Bz

Vz

Bz
Lyons & Speiser 1985 JGRSpeiser 1965 JGR

Vy

Vx
Lottermoser et al. 1998 JGRNakamura et al. 1998 JGRArzner & Scholer 2001 JGRHall effect• Magnetic field lines are draggedout of the page (Sonnerup 1979,Mandt et al. 1994)(c) T. Wada

Two Speiser orbits• Global-type (classical one)(A) Quadrupole
magnetic field

(B)

Hall

entcurr(F) Pedestal(G) Electron shock& magnetic cavity

zy(D) Dissipation regionx(C) Electron current layer(E) Electron diamagnetic jet• Local-type (local reflection)(A) Quadrupole
magnetic field

(B)

Hall

ent

curr

(F) Pedestal(G) Electron shock& magnetic cavity

zy(D) Dissipation regionx(C) Electron current layer(E) Electron diamagnetic jet

Ion velocity distribution function• (1) global Speiser ions
• (2) local Speiser ions
• (3) trapped ions

Vz

Vy

Vy

Bz

Vx
Vx

Nonlinear dynamics in 1980’s• The night before
kinetic PIC simulations• Poincaré
map:.
(x, x) at z=0

Empty islands
Sea of chaos
Mystery onion

One can visuallyclassify particle orbits.
Chen & Palmadesso 1986 JGRIon velocity distribution function
By
Vy

ZX

Vx

By
Z

Vy
X

Vx

Ion velocity distribution function
By
Vy

ZX

Vx

By
Z

Vy
XVx

Ion velocity distribution function
By
Vy

ZXVx

ByZVy
X
• Two of 5 variables (x, y, Vx, Vy, Vz) at z=0

Vx

Distribution function ⇔ Poincaré map.
. .
• (x, x) ⇔ (-y, x)

Regular orbits

Speiser orbits(Transient orbits)

Chen & Palmadesso 1986 JGR

by T. Wada @ NAOJ

http://th.nao.ac.jp/MEMBER/zenitani/research-e.html
http://th.nao.ac.jp/MEMBER/zenitani/files/regular_orbits.mp4

Vy’

Simulation vs Theory

3

PIC simulation

Z 2ZZ

10X

Vy’
Chaos model

3.53

3

2.5Z 221.5

110.500-2

Regular motion in a moving, rotated frame-10Vy’

12(Reconstructed)

Trapped-ion orbit• Decomposed to the regular motion and the frame motion• First demonstration of regular orbits in a self-consistent PIC
simulation
Trapped ion(a) 3D trajectories

zyx

Regular motion in a moving,rotated frame

3. Discussion

Particle-orbit theory
Curvature radius of B

Larmor radius

Büchner & Zelenyi 1989 JGR

B

Bounce motion

B

Chaotic motion

B

Gyro motion(μ-adiabatic)

Particle-orbit theory
Curvature radius of BLarmor radius

B

Bounce motion

B

Chaotic motion

B

Gyro motion(μ-adiabatic)

Ideal condition• The ideal condition can be easily violated• Particles no longer gyrate about B• The nonidealness is necessary, but not
sufficient for magnetic dissipation

B

Bounce motion

B

Chaotic motion

B

Gyro motion(μ-adiabatic)

Sub-Alfvénic ion flowVix• Ion flow (Vi) is slower than
the inflow Alfvén speed (cA,in)• Typically 0.4-0.5 cA,inZ• Local Speiser ionsin the rotated frame
X
Inflow Alfvén speed (cA,in)

ViVyxx
VExB=UVExB

BzVxDissipation region

Super-Alfvénic
electron jet
e-= Ensemble of theswing-by motion oflocal Speiser electrons

p+JZY

Local Speiser
electrons

X

e-Vy

VExBVeVx
Chen et al. 2011 PoP

Multiscale picture of the outflow region
Vex• Curvature radius increases
in the farther downstream• We may eventually see
MHD-like Alfvénic outflow

Vy
Super-Alfvénic
electron jet in x
[E + ve x B]y < 0Vi

VExBVeSub-Alfvénic
ion flow in x

VExBVxVx[E + vi x B]y > 0Summary• We have examined an ion velocity distribution function in
the reconnection outflow:– (1) Global Speiser ions
– (2) Local Speiser ions
– (3) Trapped ions
• Regular orbits in the chaos theory• First demonstration in PIC simulation• Plasma ideal condition– Easily violated in the κ<1 regime– Particles no longer gyrate• Local-Speiser motion explains– Sub-Alfvénic ion flow
– Super-Alfvénic electron jet• Better understanding of the outflow region
from the viewpoint of particle motion

Thank you for your attention!