空间等离子体和单粒子的运动、KineticTheory和MHD简介

1 Q exp( r )
4 0 r
D
2D

0kTe
n0e2
11
德拜长度的快速估算
D 6.9
Te n0
Debye Length in cm
Te in k n0 in cm-3
12
研究对象尺寸要求
保持等离子体电中性 L D
13
典型的德拜长度
Plasma
Solar core Tokamak Gas discharge Ionosphere Magnetosphere Solar wind Interstellar medium Intergalactic
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什么样的条件使得等离子体稳定存在？
1.保持电中性 2.自由粒子的存在 3.发生碰撞的几率低
6
德拜屏蔽(Debye Shielding)
等离子体存在一个特征长度，在此特征长
度以外，带电粒子间库仑势场因为屏蔽效应迅 速减弱。这个特征长度定义为Debye length。
D
0 k Te
n0e2
http://en.wikipedia.org/wiki/Plasma_%28physics%29 4
分离的正离子和电子是否会在电场力的库仑 相互作用下结合成电中性原子或者分子？频繁的 带电粒子碰撞对等离子体的影响是什么？
Plasma lamp
See http://en.wikipedia.org/wiki/Plasma_%28physics%29
7
Debye Length由温度和带电粒子的密度共同决定
8
Debye and Coulomb potential
库仑势
1 Q
4 0 r
德拜势
1 Q exp( r )
4 0 r
D
9
德拜屏蔽(Debye Leabharlann Baiduhielding)
统计物理指出自由粒子在相空间*的分布大致如下：
2
等离子体
等离子体的定义: 由自由电子和自由离子组成的集合体（气体），
其正负电荷数目相同。在平均作用的意义上，等离子体对 外呈现电中性。
等离子体的直接特性： 自由离子和自由电子占主导地位
（即带电粒子所受到的势能远小于粒子热 运动的动能），随机的热运动克服库仑势。
3
Property Electrical Conductivity
Independently acting species
Velocity distribution
Interactions
Gas Very low
Air is an excellent insulator until it breaks down into plasma at electric field strengths above 30 kilovolts per centimeter. One All gas particles behave in a similar way, influenced by gravity and by collisions with one another.
Plasma
Usually very high
For many purposes, the conductivity of a plasma may be treated as infinite.
Two or three
Electrons, ions, protons and neutrons can be distinguished by the sign and value of their charge so that they behave independently in many circumstances, with different bulk velocities and temperatures, allowing phenomena such as new types of waves and instabilities.
Collective
Waves, or organized motion of plasma, are very important because the particles can interact at long ranges through the electric and magnetic forces.
Often non-Maxwellian
Collisional interactions are often weak in hot plasmas and external forcing can drive the plasma far from local equilibrium and lead to a significant population of unusually fast particles.
空间等离子体和单粒 子的运动、Kinetic Theory 和 MHD 简介
1
Outline:
等离子体的定义
Debye长度和等离子体 的特性
空间等离子体
单个带电粒子的运动 回旋波 Guiding center motion
磁矩守恒量 磁镜效应
Trapped particles 辐射带 电离层 极光的产生 磁冻结效应 Kinetic theory简介 MHD简介
Maxwellian Collisions usually lead to a Maxwellian velocity distribution of all gas particles, with very few relatively fast particles.
Binary Two-particle collisions are the rule, three-body collisions extremely rare.
3
fe
(v)

n0
me
2kTe
2
exp
1 2
meV 2 k Te
q

*相空间指（vx, vy, vz, rx, ry, rz）组成的坐标空间
10
解Poisson方程
2
q 0


n0e
0
1

exp
e k Te