EGU2014-3245

The secrets of the ion diffusion
region in collisionless magnetic
reconnection
Seiji ZENITANI
National Astronomical
Observatory of Japan

I. Shinohara (JAXA/ISAS)
T. Nagai (Titech)
T. Wada (NAOJ)Electron-scalestructure
Ion-scalestructure(E+vi xB)yInflow Alfvén

Z

speed, cA,in(A) Quadrupole
magnetic field(B)

-By

Hal

nt
urrelc(F) Pedestal+By(D) Dissipation regionzy(C) Electron current layerxZenitani et al. 2011 PoPX(E) Super-Alfvénic electron jetHybridNakamura et al. 1998 JGRLottermoser et al. 1998 JGRArzner & Scholer 2001 JGRHigashimori & Hoshino 2012 JGR
30-40% of inflow Alfvén
speed
Kinetic
Karimabadi et al. 2007
GRL
Drake et al. 2009 JGR
Bessho & Bhattacharjee
PoP
Liu et 2010
al. 2011--2012
PoP•Q1. Is this a “[ion] diffusion region”?
•Q2. Why is the ion ideal condition violated?
•Q3. Why is the ion flow sub-Alfvénic?

Magnetic diffusion• Arbitrary Ohm’s law

Frozen-in condition

Magnetic diffusion(Flux preservation)

Bv• Relaxation to the frozen-in state

Newcomb 1958Stern 1966, Vasyliunus 1972,
Scudder 1997, Hornig 2001

Relative concepts that depend
on a reference velocity field v

Violation of the flux frozen-in

Frozen-in condition(Flux preservation)

No energy conversion
Reconnection

Energy conversion
Diffusion in a narrow sense

Additional compression
or expansion

Newcomb 1958

Zenitani & Umeda 2014

Violation ofLine preservation

Newcomb 1958

Effective magnetic diffusivity
Nonideal(E+vi xB)yZ

X

Electron diffusion region
based on its literal meaning

Ion diffusion region
based on its literal meaning

Frozen-in
2D PIC simulationsIon velocity distribution function(E+vi xB)yZX• Non-ideal, but outside
the ion diffusion region

Vy• Non-Maxwellian

Bz
Vx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

Vy
VExB
Bz

Vx

Vx

(Local-type) Speiser orbit

ZBz

Vz

Bz
Lyons & Speiser 1985 JGRSpeiser 1965 JGR

Vy

VxLottermoser et al. 1998 JGRNakamura et al. 1998 JGR

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

Empty islands

Sea of chaos
Great onion

One can visuallyclassify particle orbits.
Chen & Palmadesso 1986 JGRParticle-orbit theory
Nonlinear system

Curvatureradius of B

Büchner & Zelenyi 1989 JGR

B

Larmor radius

B

B??
Bounce motion(I-adiabatic)

Chaotic motion
Footprint = Poincaré map

Gyro motion(μ-adiabatic)

Ion distribution function
By
VyZXVxByZVyXVx

Ion distribution function
By
Vy

ZXVx

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

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

Trapped ionsPhase diagram @x=51

3 orbitRegularZ 2Mainpopulation

10Vy’
3.5332.5Z 22Orbit theory

1.5

8-shaped regular orbit

110.500-2-10

Vy’12

Macroscopic properties
Vx along the outﬂow line
Inflow Alfvén speed (cA,in)

ViVyVExBx
VExB

VExB

ViXx

Bz
|Vi -VExB| sinα

Vx
slow

• Slow outflow: An apparent effect• Nonidealness: Nongyrotropic motion• Speiser ions do not fully gyrate about Bz !!

Dissipation region

Sub-Alfvénic
ion flow
ep+= Ensemble of theswing-by motion oflocal Speiser ions
Local Speiserions

ZYXiViVyxx
VExB

BzVxslowDissipation region

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

p+JZY

Local Speiserelectrons

Xe-Vy

VExB
VeVx
Chen et al. 2011 PoPText summary• Magnetic diffusion– Relaxation to the frozen-in state

relax– Relative concept that depends on one’s choice of v
– Ion diffusion region is smaller than the Riy ≠ 0 region• Poincaré map ⇔ Ion velocity distribution function– Nongyrotropic particle motion– (1) Global Speiser ions
– (2) Local Speiser ions
• Violation of the ideal condition• Sub-Alfvénic ion flow

– (3) Trapped ions: (NEW)• Regular orbits in the chaos theory• References– Zenitani, Shinohara, Nagai, & Wada, Phys. Plasmas, 20, 092120 (2013)– Zenitani & Umeda, Phys. Plasmas, 21, 034503 (2014)– Zenitani, Hesse, Klimas, & Kuznetsova, Phys. Rev. Lett., 106, 195003 (2011)

Visual summary
Electron Diffusion Region
Dissipation Region

Nongyrotropic layers

Ion Diffusion Region
Magnetic dissipation(Zenitani+ 2011 PRL)
relaxMagnetic diffusion(Zenitani & Umeda 2014 PoP)

Nongyrotropic motion(Zenitani+ 2013 PoP)

• The ion diffusion region is smaller than thought:
Ion nongyrotropic physics dominates in the outer layer