阿爾文波

阿爾文波，又稱剪切阿爾文波，是等離子體中的一種沿磁場方向傳播的波，這種波的頻率遠低於等離子體的迴旋頻率，是一種線偏振的低頻橫波。處在磁場中的導電流體在垂直於磁場的方向上受到局部擾動時，沿着磁感線方向的磁張力提供恢復力，就會激發阿爾文波。阿爾文波是由瑞典物理學家漢尼斯·阿爾文首先預言的，因此得名。後來隆德奎斯特（Lundquist）使用1特斯拉左右的磁場在水銀中觀察到了阿爾文波，列納爾特（Lehnert）使用液態鈉也證實了阿爾文波的存在。

運動的阿爾文波。

A cluster of double layers forming in an Alfvén wave, about a sixth of the distance from the left.
圖例:
紅色=electrons
綠色=ions
黃色=electric potential
橙色=parallel electric field
粉色=charge density
藍色=magnetic field

阿爾文波的色散關係為：

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

這樣的波稱為斜阿爾文波。θ=0時是沿着磁感線的方向傳播的，稱為阿爾文波。此時阿爾文波的相速度為：

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

稱為阿爾文速度，其中μ₀是等離子體的磁導率，ρ₀是離子的密度。在垂直於磁感線的方向上阿爾文波不能傳播。

阿爾文時間

在等離子體物理中, 阿爾文時間${\displaystyle \tau _{A}}$是波動現象的一個重要時標。它和阿爾文速度的關係為：

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

式中${\displaystyle a}$ 代表了系統的特徵尺度。例如，${\displaystyle a}$ 是托卡馬克中較小的環的半徑。

參見

• 壓縮阿爾文波

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