阿爾文波
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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。
阿爾文波的色散關係為:
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:
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, 阿爾文時間是波動現象的一個重要時標。它和阿爾文速度的關係為:
式中 代表了系統的特徵尺度。例如, 是托卡馬克中較小的環的半徑。
參見
延伸閱讀
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