2. 空间等离子体和单粒子的运动、 kinetic theory 和 mhd 简介
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空间物理学( I ). 2. 空间等离子体和单粒子的运动、 Kinetic Theory 和 MHD 简介. 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. 等离子体. 等离子体的定义 : - PowerPoint PPT PresentationTRANSCRIPT
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
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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。
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Property Gas Plasma
Electrical Conductivity
Very low
Air is an excellent insulator until it breaks down into plasma at electric field strengths above 30 kilovolts per centimeter.
Usually very high
For many purposes, the conductivity of a plasma may be treated as infinite.
Independently acting species
One All gas particles behave in a similar way, influenced by gravity and by collisions with one another.
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.
Velocity distribution
Maxwellian
Collisions usually lead to a Maxwellian velocity distribution of all gas particles, with very few relatively fast particles.
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.
Interactions Binary
Two-particle collisions are the rule, three-body collisions extremely rare.
Collective
Waves, or organized motion of plasma, are very important because the particles can interact at long ranges through the electric and magnetic forces.
http://en.wikipedia.org/wiki/Plasma_%28physics%29
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See http://en.wikipedia.org/wiki/Plasma_%28physics%29
Plasma lamp
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?
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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 。
20
0
en
kTeD
10
德拜屏蔽 (Debye Shielding)
统计物理指出自由粒子在相空间 * 的分布大致如下:
e
e
e
e
kT
qVm
kT
mn
2212
3
0e exp2
(v)f
* 相空间指( vx, vy, vz, rx, ry, rz )组成的坐标空间
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典型的德拜长度Plasma
Densitne(m
-3)
Electron temperature
T(K)
MagneticFieldB(T)
DebyeLengthλD(m)
Solar core 1032 107 -- 10−11
Tokamak 1020 108 10 10−4
Gas discharge 1016 104 -- 10−4
Ionosphere 1012 103 10−5 10−3
Magnetosphere 107 107 10−8 102
Solar wind 106 105 10−9 10
Interstellar medium 105 104 10−10 10
Intergalactic medium
1 106 -- 105
http://en.wikipedia.org/wiki/Debye_length#Debye_length_in_silicon
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如何联系自由带电粒子和 ND ?
1
ekT
e库仑势能远小于粒子热运动的动能
考虑极限条件下:31
1min
enr
于是:
min04
1
r
e
32
31 1
4
1
4
1 2
0 D
eee Nn
kT
e
kT
e
1
ekT
e 13 DeD nN