SM12A-04 Magnetic diffusion and ion nonlinear dynamics in magnetic reconnection

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1 SM12A-04 Magnetic diffusion and ion nonlinear dynamics in magnetic reconnection Seiji ZENITANI National Astronomical Observatory of Japan Collaborators: I. Shinohara (JAXA/ISAS), T. Nagai (Titech), T. Wada (NAOJ), T. Umeda (Nagoya U)

2 Electron-scale structure (A) Quadrupole magnetic field -B y (B) Hall current (F) Pedestal z y x Zenitani et al PoP +B y (D) Dissipation region (C) Electron current layer (E) Super-Alfvénic electron jet

3 Ion-scale Electron-scale structure Z (A) Quadrupole magnetic field -B y (B) Hall current (F) Pedestal X +B y (D) Dissipation region z (C) Electron current layer (E) Super-Alfvénic electron jet y x Zenitani et al PoP Hybrid Nakamura et al JGR Lottermoser et al JGR Arzner & Scholer 2001 JGR Higashimori & Hoshino 2012 JGR Kinetic Drake et al JGR Liu et al PoP

4 Ion-scale Electron-scale structure Inflow Alfvén speed, c A,in Z (A) Quadrupole magnetic field -B y (B) Hall current (F) Pedestal X +B y (D) Dissipation region z (C) Electron current layer (E) Super-Alfvénic electron jet y x Zenitani et al PoP Hybrid Nakamura et al JGR Lottermoser et al JGR Arzner & Scholer 2001 JGR Higashimori & Hoshino 2012 JGR 30-40% of inflow Alfvén Kinetic speed Karimabadi et al Drake GRL et al JGR Bessho & Bhattacharjee Liu et 2010 al PoP PoP

5 Ion-scale Electron-scale structure Inflow Alfvén speed, c A,in Z (A) Quadrupole magnetic field -B y (B) Hall current (F) Pedestal X y z x +B y Zenitani et al PoP (D) Dissipation region (C) Electron current layer (E) Super-Alfvénic electron jet Hybrid Nakamura et al JGR Lottermoser et al JGR Arzner & Scholer 2001 JGR Higashimori & Hoshino 2012 JGR 30-40% of inflow Alfvén Kinetic speed Karimabadi et al Drake GRL et al JGR Bessho & Bhattacharjee Liu et 2010 al PoP PoP Q1. Is this a [ion] diffusion region? Q2. Why is the ion ideal condition violated? Q3. Why is the ion flow sub-alfvénic?

6 Diffusion Something spreads out Relaxation to a flat state

7 Magnetic diffusion Arbitrary Ohm s law Frozen-in condition (Flux preservation) Magnetic diffusion B v Relaxation to the frozen-in state Newcomb 1958 Stern 1966, Vasyliunus 1972, Scudder 1997, Hornig 2001

8 Magnetic diffusion Arbitrary Ohm s law Frozen-in condition (Flux preservation) Magnetic diffusion B v Relaxation to the frozen-in state Newcomb 1958 Stern 1966, Vasyliunus 1972, Scudder 1997, Hornig 2001 Relative concepts that depend on a reference velocity field v

9 Effective magnetic diffusivity Nonideal Z X Electron diffusion region based on its literal meaning Ion diffusion region based on its literal meaning Frozen-in 2D PIC simulations

10 Ion velocity distribution function Z X Vy Non-ideal, but outside the ion diffusion region Non-Maxwellian B z Vx

11 Ion velocity distribution function (1) global Speiser ions (2) local Speiser ions (3) trapped ions Vz Vy Vy B z Vx Vx

12 (Local-type) Speiser orbit Z B z Vz Vy B z Vx Lyons & Speiser 1985 JGR Speiser 1965 JGR Lottermoser et al JGR Nakamura et al JGR

13 Ion velocity distribution function (1) global Speiser ions (2) local Speiser ions (3) trapped ions Vz Vy Vy B z Vx Vx

14 Nonlinear dynamics in 1980 s The night before kinetic PIC simulations Poincaré. map: (x, x) at z=0 Empty islands Sea of chaos Great onion One can visually classify particle orbits. Chen & Palmadesso 1986 JGR

15 Distribution function Poincaré map... (x, x) (-y, x) Regular orbits Speiser orbits (Transient orbits) Chen & Palmadesso 1986 JGR

16 Confined on a hyper-surface by T. NAOJ

17 Particle orbits 3 Regular orbit Phase Z 2 1 Main population 0 Vy 8-shaped regular orbit Z Vy Orbit theory

18 Macroscopic properties VExB Inflow Alfvén speed (ca,in) Vy Vi x x V ExB VExB Vi B z X Vx Slow outflow: An apparent effect Nonidealness: Nongyrotropic motion Speiser ions do not fully gyrate about Bz!!

19 Macroscopic properties VExB Inflow Alfvén speed (ca,in) Vy Vi x x V ExB VExB X Vi Vi -VExB sinα Vx B z slow Slow outflow: An apparent effect Nonidealness: Nongyrotropic motion Speiser ions do not fully gyrate about Bz!!

20 Ion-scale Electron-scale structure Z y z x (A) Quadrupole magnetic field -B y +B y Zenitani et al PoP (D) Dissipation region (C) Electron current layer (B) Hall current (F) Pedestal (E) Super-Alfvénic electron jet HERE Q1. Is this a diffusion region? X No. Q2. Why is the ion ideal condition violated? Q3. Why is the ion flow sub-alfvénic? Nongyrotropic ion motion is responsible.

21 Magnetic diffusion Summary Relaxation to the frozen-in state Relative concept that depends on one s choice of v 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 Better understanding of the reconnection outflow region, both from the macroscopic and microscopic viewpoints

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23 Thank you for your attention! Zenitani, Shinohara, Nagai, & Wada, Phys. Plasmas, 20, (2013) Zenitani & Umeda, Phys. Plasmas, to be submitted