Particle dynamics in the electron
current layer in collisionlessmagnetic reconnection
Seiji ZENITANI
National Astronomical Observatory of Japan
Key points:• We study electron orbits in symmetric reconnection with PIC simulation.
• We are introducing an electron figure-8 shaped orbit.
• We are introducing a new family of electron orbits.

Magnetospheric Multiscale (MMS) mission• MMS is going to observe the Earth’s magnetotail in 2017,
where symmetric antiparallel reconnection takes place.
• MMS is the first mission to observe electron Velocity
Distribution Function (VDF) at unprecedented resolution.

Electron VDFs in PIC simulation

6x4Chen+ 2008 JGR• Many PIC studies on electron VDFs [in symmetric reconnection]• Hoshino+ 2001, Pritchett 2006, Chen+ 2008, 2009, Ng+ 2011, 2012, Hesse+ 2011, Bessho+ 2014,
Shuster+ 2014, 2015, Cheng+ 2015

6x4

Electron VDFs vs electron orbits
VDFs

Orbits-By

B
Egedal orbit
igne
d-alleiw
F
inflodDissipation
regionLocal
Speiser orbitzyGlobal Speiser
orbit+Byx-B• In addition to VDFs,
we have to understandelectron orbits, too.
• We examine 2x107 selfconsistent electron orbits
in our PIC simulation

Speiser VDFs in PIC simulation
Global Speiser
via EDR
Local Speiserof pickup type

Vex : electron jets

Z

321Z

0-1-2-3
35

40

35

40

45

50

45

50

0

Vey-5

Y -10-15-20

Vex

32.5

123X

Regular (integrable) orbits(b) VexZz

Trapped in a figure-8
shaped orbit (κ~0.2)

2.5
21.5
10.5

Z

0-0.5
-1-1.5-236

38

40

42

44

46

48

20-2-4

X

Chen & Palmadesso 1986 JGRClass of particle orbits
Global-type
Speiser orbits

Local-type
Speiser orbits

Regular orbits

Noncrossing
electrons

Zenitani+ 2016

Zenitani+ 2016

Zenitani+ 2016

Electrons

Speiser 1965

(Straightforward)

Zenitani+ 2016

Speiser 1965

Nakamura+ 1998,
Lottermoser+ 1998,
Drake+ 2009

Zenitani+ 2013

Ions

Noncrossing Speiser-like orbits
2D 3orbits
2.52Zz

(d)

(a)

6

1.5

4

1
2

0.5

Midplanevey 00-0.5

3D orbit35

40

10-1(b)X

45

50-2-4

Electrostatic field Ez-6-2y -3Ez
-4 x B drift +E-5// acceleration-6-7Midplane

-8

ε0.35
0.3

1-Ez

0.8

12
30.6Ez35404550

z 0.40.2-2

Noncrossing regular orbits
Trapped on flanks ofthe electron jet

2.5
2
1.5

10100.55

51Z

0-0.500-1-5-1.5-5-2-1036

3840

42-10

2

0 -10-5051015Phase-space
diagrams-2
144X-10-5

46

05

48

1015

1-4

Chen & Palmadesso 1986 JGR-60.5-8-10Z -120-14

0.512343638-0.50.9

Detached fromthe midplane,48
due to Ez

040

4244-0.5

460.8
0.7-1
0.6
0.5
0.4

-10-505Vx

1015-1-10-50Vz

510

Noncrossing electrons are non-negligible(f) NElectrondensityez(a) Noncrossing electronsz

Observational signatures: ET diagram
PIC simulation(a) z=0.0• Speiser-accelerated electrons• Low-energy electrons are absent

log10ε• Midplane (super-Alfvénic e jet)x
Low-energy electrons-Ez

keVEz

Geotail observationtime

2007-05-05 (Nagai+ 2013 JGR)

Summary-By
Super-Alfvénic
electron jet

By

Speiser orbit

Noncrossing local
Speiser orbit

Egedal orbit

Field -a li
inflo gnedw

Crossing
regular orbit☆

Dissipation
regionLocal
Speiser orbitz☆ Noncrossing global

Nongyrotropic
electrons

Noncrossing
regular orbit

GlobalSpeiser orbit+Byx-B

PSBL electron
outflow

Zenitani+ 2016a in prep.

• Many NEW electron orbits in magnetic reconnection• Noncrossing electrons appear to be important• Consistent with Geotail ET-diagram