阿尔文波
外观
(重定向自阿尔芬速度)
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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(Lundquist)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(Lehnert)使用液态钠也证实了阿尔文波的存在。
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b4/Alfven-wave-double-layer.gif/220px-Alfven-wave-double-layer.gif)
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:
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:
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
[编辑]在等离子体物理中, 阿尔文时间是波动现象的一个重要时标。它和阿尔文速度的关系为:
式中 代表了系统的特征尺度。例如, 是托卡马克中较小的环的半径。
参见
[编辑]延伸阅读
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