Thermal conduction in a mirror-unstable plasma
Thermal conduction in a mirror-unstable plasma
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DOI：
10.1093/mnras/stw963
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发表时间：
2016-07-21
影响因子：
4.8
通讯作者：
Schekochihin, A. A.
中科院分区：
文献类型：
--
作者：
Komarov, S. V.;Churazov, E. M.;Schekochihin, A. A.
星系团的等离子体在离子拉莫尔半径的量级上会受到火管和镜像不稳定性的影响。镜子的不稳定性会产生类似于 1 的磁场强度 delta B/B 波动。这些波动充当热传导电子的磁陷阱，抑制其传输。我们计算了在不稳定性演化的不同阶段存在镜像涨落的情况下 ICM 中的有效平行热导率。镜子波动的幅度受到场强的最大值和最小值的限制，与平均值没有大的偏差。这一关键特性导致对大尺度热传导的有限抑制。我们发现扰动增长的长期阶段的斯皮策值的抑制大约为 0.2，饱和阶段的抑制大约为 0.3。该效应与其他抑制机制一起发挥作用，并且独立于其他抑制机制。在全球范围内，类似于 1 的波动 Delta B/B 可以出现在更大的尺度上，相当于湍流运动的尺度。然而，我们并不期望这些对热传导有很大的抑制，因为它们的规模比 ICM 电子的碰撞平均自由程大得多。所获得的热传导抑制系数约为 5 倍似乎是弱碰撞镜面不稳定等离子体的特征，并且可能具有普遍性。
The plasma of galaxy clusters is subject to firehose and mirror instabilities at scales of order the ion Larmor radius. The mirror instability generates fluctuations of magnetic-field strength delta B/B similar to 1. These fluctuations act as magnetic traps for the heat-conducting electrons, suppressing their transport. We calculate the effective parallel thermal conductivity in the ICM in the presence of the mirror fluctuations for different stages of the evolution of the instability. The mirror fluctuations are limited in amplitude by the maximum and minimum values of the field strength, with no large deviations from the mean value. This key property leads to a finite suppression of thermal conduction at large scales. We find suppression down to approximate to 0.2 of the Spitzer value for the secular phase of the perturbations' growth, and approximate to 0.3 for their saturated phase. The effect operates in addition to other suppression mechanisms and independently of them. Globally, fluctuations delta B/B similar to 1 can be present on much larger scales, of the order of the scale of turbulent motions. However, we do not expect large suppression of thermal conduction by these, because their scale is considerably larger than the collisional mean free path of the ICM electrons. The obtained suppression of thermal conduction by a factor of similar to 5 appears to be characteristic and potentially universal for a weakly collisional mirror-unstable plasma.