阿尔文波

阿尔文波，又称剪切阿尔文波，是等离子体中的一种沿磁场方向传播的波，这种波的频率远低于等离子体的回旋频率，是一种线偏振的低频横波。处在磁场中的导电流体在垂直于磁场的方向上受到局部扰动时，沿着磁感线方向的磁张力提供恢复力，就会激发阿尔文波。阿尔文波是由瑞典物理学家汉尼斯·阿尔文首先预言的，因此得名。后来隆德奎斯特（）使用1特斯拉左右的磁场在水银中观察到了阿尔文波，列纳尔特（）使用液态钠也证实了阿尔文波的存在。

A cluster of double layers forming in an Alfvén wave, about a sixth of the distance from the left.
图例:
红色=electrons
绿色=ions
黄色=electric potential
橙色=parallel electric field
粉色=charge density
蓝色=magnetic field

阿尔文波的色散关系为：

\omega ^{2}=k^{2}v_{A}^{2}\cos ^{2}\theta

这样的波称为斜阿尔文波。θ=0时是沿着磁感线的方向传播的，称为阿尔文波。此时阿尔文波的相速度为：

v_{A}={\frac {B}{\sqrt {\mu _{0}\rho _{0}}}}

称为阿尔文速度，其中μ₀是等离子体的磁导率，ρ₀是离子的密度。在垂直于磁感线的方向上阿尔文波不能传播。

阿尔文时间

在等离子体物理中, 阿尔文时间 $\tau _{A}$ 是波动现象的一个重要时标。它和阿尔文速度的关系为：

\tau _{A}={\frac {a}{v_{A}}}

式中 $a$ 代表了系统的特征尺度。例如， $a$ 是托卡马克中较小的环的半径。

参见

压缩阿尔文波

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