镜像不稳定等离子体中热传导的抑制
Suppression of thermal conduction in a mirror-unstable plasma
摘要：
ICM等离子体在离子拉莫尔半径量级的尺度上会受到水龙带和镜像不稳定性的影响。镜面不稳定性产生磁场强度的波动$δB / B \sim 1$。这些波动作为热传导电子的磁陷阱，抑制它们的传输。我们计算的有效平行的ICM中的不稳定性的演化的不同阶段的镜像波动的存在下的热导率。镜像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。这一关键性质导致在大尺度上对热传导的有限抑制。我们发现抑制到$\approx 0.2$的斯皮策值的长期阶段的扰动的增长，和$\approx 0.3$的饱和阶段。这种效应除了其他抑制机制之外，还独立于它们发挥作用。在全球范围内，波动$δB / B \sim 1$可以出现在更大的尺度上，其量级为湍流运动的尺度。然而，我们并不期望这些大的抑制热传导，因为它们的规模是相当大的比ICM电子的碰撞平均自由程。所获得的抑制热传导的一个因素的$\sim 5$似乎是一个弱碰撞镜像不稳定等离子体的特性和潜在的普遍性。
英文摘要：
The ICM plasma is subject to firehose and mirror instabilities at scales of order the ion Larmor radius. The mirror instability generates fluctuations of magnetic-field strength $δB / B \sim 1$. 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 $\approx 0.2$ of the Spitzer value for the secular phase of the perturbations' growth, and $\approx 0.3$ for their saturated phase. The effect operates in addition to other suppression mechanisms and independently of them. Globally, fluctuations $δB / B \sim 1$ 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 $\sim 5$ appears to be characteristic and potentially universal for a weakly collisional mirror-unstable plasma.
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