扩展无感磁旋转不稳定性的范围
Extending the range of the inductionless magnetorotational instability
摘要：
磁旋转不稳定性（MRI）可以破坏流体动力学稳定的旋转流，从而允许在吸积盘的角动量输运。磁共振成像的一个臭名昭著的问题是它在低磁普朗特数区域的适用性值得怀疑，因为它们是原行星盘和黑洞周围吸积盘外部的典型区域。使用WKB方法，我们扩展了MRI的适用范围，证明了如果方位磁场的径向分布仅与无电流分布~ 1/r略有不同，则无感应形式的MRI（如螺旋MRI和方位MRI）很容易使开普勒分布~ 1/r^（3/2）不稳定。这样，我们进一步展示了以前已知的临界Rossby数的下限Ro=-0.828与上限Ro=+4.828之间的自然联系。
英文摘要：
The magnetorotational instability (MRI) can destabilize hydrodynamically stable rotational flows, thereby allowing angular momentum transport in accretion disks. A notorious problem for MRI is its questionable applicability in regions with low magnetic Prandtl number, as they are typical for protoplanetary disks and the outer parts of accretion disks around black holes. Using the WKB method, we extend the range of applicability of MRI by showing that the inductionless versions of MRI, such as the helical MRI and the azimuthal MRI, can easily destabilize Keplerian profiles ~ 1/r^(3/2) if the radial profile of the azimuthal magnetic field is only slightly modified from the current-free profile ~ 1/r. This way we further show how the formerly known lower Liu limit of the critical Rossby number, Ro=-0.828, connects naturally with the upper Liu limit, Ro=+4.828.
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