Title: Suppression of thermal conduction in a mirror-unstable plasma Show Chinese title

Title: 镜面不稳定性等离子体中的热传导抑制

Abstract: 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 $\delta B / B \sim 1$. 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 $\delta B / B \sim 1$ 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. Show Chinese abstract

Abstract: ICM等离子体在离子回旋半径量级的尺度上会受到火舌不稳定性与镜像不稳定性的影响。 镜像不稳定性会产生磁场强度的波动，$\delta B / B \sim 1$。 这些波动作为磁约束，抑制热传导电子的输运。 我们计算了在镜像波动存在的情况下，ICM中不同不稳定性演化阶段的有效平行热导率。 镜像波动的幅度受到磁场强度最大值和最小值的限制，与平均值没有大的偏离。 这一关键特性导致在大尺度上热传导的有限抑制。 我们发现，在扰动增长的长期阶段，抑制程度达到Spitzer值的$\approx 0.2$，而在其饱和阶段为$\approx 0.3$。 该效应除了其他抑制机制之外独立起作用。 全局来看，波动$\delta B / B \sim 1$可以出现在比湍流运动尺度大得多的尺度上。 然而，我们并不期望这些波动对热传导产生显著抑制，因为它们的尺度明显大于ICM电子的碰撞平均自由程。 通过一个因子$\sim 5$的热传导抑制似乎对于弱碰撞的镜像不稳定等离子体是特征性的且可能具有普遍性。