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)
Electron-scale structure (A) Quadrupole magnetic field -B y (B) Hall current (F) Pedestal z y x Zenitani et al. 2011 PoP +B y (D) Dissipation region (C) Electron current layer (E) Super-Alfvénic electron jet
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. 2011 PoP Hybrid Nakamura et al. 1998 JGR Lottermoser et al. 1998 JGR Arzner & Scholer 2001 JGR Higashimori & Hoshino 2012 JGR Kinetic Drake et al. 2009 JGR Liu et al. 2011--2012 PoP
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. 2011 PoP Hybrid Nakamura et al. 1998 JGR Lottermoser et al. 1998 JGR Arzner & Scholer 2001 JGR Higashimori & Hoshino 2012 JGR 30-40% of inflow Alfvén Kinetic speed Karimabadi et al. 2007 Drake GRL et al. 2009 JGR Bessho & Bhattacharjee Liu et 2010 al. 2011--2012 PoP PoP
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. 2011 PoP (D) Dissipation region (C) Electron current layer (E) Super-Alfvénic electron jet Hybrid Nakamura et al. 1998 JGR Lottermoser et al. 1998 JGR Arzner & Scholer 2001 JGR Higashimori & Hoshino 2012 JGR 30-40% of inflow Alfvén Kinetic speed Karimabadi et al. 2007 Drake GRL et al. 2009 JGR Bessho & Bhattacharjee Liu et 2010 al. 2011--2012 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?
Diffusion Something spreads out Relaxation to a flat state
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
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
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
Ion velocity distribution function Z X Vy Non-ideal, but outside the ion diffusion region Non-Maxwellian B z Vx
Ion velocity distribution function (1) global Speiser ions (2) local Speiser ions (3) trapped ions Vz Vy Vy B z Vx Vx
(Local-type) Speiser orbit Z B z Vz Vy B z Vx Lyons & Speiser 1985 JGR Speiser 1965 JGR Lottermoser et al. 1998 JGR Nakamura et al. 1998 JGR
Ion velocity distribution function (1) global Speiser ions (2) local Speiser ions (3) trapped ions Vz Vy Vy B z 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 Great onion One can visually classify particle orbits. Chen & Palmadesso 1986 JGR
Distribution function Poincaré map... (x, x) (-y, x) Regular orbits Speiser orbits (Transient orbits) Chen & Palmadesso 1986 JGR
Confined on a hyper-surface 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
Particle orbits 3 Regular orbit Phase diagram @x=51 Z 2 1 Main population 0 Vy 8-shaped regular orbit Z 3.5 3 3 2.5 2 2 1.5 1 1 0.5 0 0-2 -1 0 1 2 Vy Orbit theory
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!!
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!!
Ion-scale Electron-scale structure Z y z x (A) Quadrupole magnetic field -B y +B y Zenitani et al. 2011 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.
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
Thank you for your attention! Zenitani, Shinohara, Nagai, & Wada, Phys. Plasmas, 20, 092120 (2013) Zenitani & Umeda, Phys. Plasmas, to be submitted