Magnetic Reconnection— Questions &
Challenges
Xiaogang Wang
School of Physics, Peking UniversityIFTS, Zhejiang University
Sept 23 2007, Suzhou, China
OUTLINE
• What we have known• What we don’t know• Possible answers• Brief summary
What we have known
• Hall effect physics– Alfven frequency whistler waves– Quadruple field– Fast reconnection rate 0.01 ~ 0.2VA
– Layer width of reconnecting field ~ di
– Electrical potential well on separatrix
What we have known
• In question– Layer length of reconnecting field ~
(diL)1/2
– Reconnecting rate ~ (di/L)1/2
– Electron density dip on separatrix (numerically observed)
– Lower hybrid oscillations (observed) – Electron Alfven speed disturbance
(observed)
What we have known
•3D reconnection features– The existence of magnetic nulls
(observed)–Null-null line (Separator,
observed)–Spines and fans (observed)– Lower hybrid waves on the
separator (observed)
What we have known
•3D reconnection features– Electron density peak on separato
r (observed)– Electrical potential well on separa
tor (observed)– Langmuir oscillation near separat
or (observed)
What we don’t know
• 电子惯性区中的波动,特别是低杂波的激发与传播;
• 电子惯性区(包括分形线)中的密度 sh 上升?下降? —— 原因及后果;
• 重联过程中的电子加热机制?• 电子 Alfven 波的存在?• Electron hole 的产生原因以及电子声
波是否存在?
What we don’t know
• 电子压强梯度张量非对角项的贡献;• 重联率的 Scaling 的继续研究;• 电子惯性是否对重联率有贡献?• Whistler or 离子波的贡献、观测及其
与其他模式(比如 LHW )的耦合? • 剪切流对重联结构和重联率的影响
What we don’t know
• Hall 四极分布是否就是 Whistler or Alfven 频率 whistler 的驻波表现?
• 边界驱动对无碰撞磁重联的影响?
What we don’t know (3D)
• 3D 重联中的 Hall 四极分布问题?• Separator 上的电子加热机制及其与
2D 理论的对比?• Anti-parallel reconnection vs. Co
mponent reconnection ( 理论、观测上,对重联率的影响 )?
What we don’t know (3D)
• Null 以及 Null-null line 的产生机制( X-line 不稳定导致 null pair 产生是否是唯一机制)?
• 3D 重联的动力学理论( Theory of 3D reconnection dynamics )
• 单个 Null 与 Null pair 对重联发生和重联率大小的影响
Possible answers
• 应用回旋动力学理论研究电子压强梯度张量非对角项的贡献;
• 重联率 Scaling 的实验研究;• 双流体理论、回旋动力学理论中 Whistler or Alfv
en 频率 whistler 与其它模式(如 LHW )的耦合;
• 剪切流及 Alfven 共振研究 • 边界驱动无碰撞磁重联研究( Hall MHD + Hybri
d codes)
Possible answers
• Separator 上的磁镜效应及电子加速与加热机制
• Anti-parallel reconnection — Component reconnection :一个过程的两种表现形式;统计研究
SUMMARY
• Hall effects well understood• Electron dynamics not• 3D features getting attentions
• MHD & Magnetic reconnection FTP (PKU, ZJU, NAOC, USTC, DLUT)