Dynamical stability of a thermally stratified intracluster medium with anisotropic momentum and heat transport
Dynamical stability of a thermally stratified intracluster medium with anisotropic momentum and heat transport
复制标题
具有各向异性动量和热传输的热分层簇内介质的动态稳定性
DOI：
10.1111/j.1365-2966.2011.19303.x
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发表时间：
2011
影响因子：
4.8
通讯作者：
M. Kunz
中科院分区：
文献类型：
--
作者：
M. Kunz
在弱碰撞等离子体中，例如簇内介质（ICM），热量和动量传输相对于局部磁场方向变得各向异性。当温度沿重力方向升高时，各向异性热传导导致慢磁声波变得浮力不稳定，导致磁热不稳定性（MTI）；当温度沿重力方向降低时，慢磁声波变得不稳定，导致热通量驱动的浮力不稳定（HBI）。引起这些不稳定性的磁场强度的局部变化会导致压力各向异性，从而粘性阻尼平行于磁场的运动。在本文中，我们采用线性稳定性分析来阐明各向异性粘度（即 Braginskii 压力各向异性）对 MTI 和 HBI 的影响。通过抑制磁场线的会聚/发散，压力各向异性显着影响 ICM 与温度梯度的相互作用。依赖于磁场线会聚/发散产生不稳定浮力运动（H BI）的不稳定性在大部分波数空间上被抑制，而那些受场线会聚/发散（MTI）阻碍的不稳定性则得到加强。因此，HBI 在 ICM 中基本上不受抑制的波数具有太小的并行分量，无法严格视为局部波数。当磁场变得越来越与温度梯度正交时尤其如此。最近的数值模拟发现，场线绝缘是标准 HBI 的非线性结果，因此可能会减弱。相比之下，增长最快的 MTI 模式不受各向异性粘度的影响。然而，我们
In weakly-collisional plasmas such as the intracluster medium (ICM), heat and momentum transport become anisotropic with respect to the local magnetic field direction. Anisotropic heat conduction causes the slow magnetosonic wave to become buoyantly unstable to the magnetothermal instability (MTI) when the temperature increases in the direction of gravity and to the heat-flux‐driven buoyancy instability (HBI) when the temperature decreases in the direction of gravity. The local changes in magnetic field str ength that attend these instabilities cause pressure anisotropies that viscously damp motions parallel to the magnetic field. In this paper we employ a linear stability analysis to elucidate the effects of anisotropic viscosity (i.e. Braginskii pressure anisotropy) on the MTI and HBI. By stifli ng the convergence/divergence of magnetic field lines, pressure anisotropy significantly a ffects how the ICM interacts with the temperature gradient. Instabilities which depend upon the convergence/divergence of magnetic field lines to generate unstable buoyant motions (the H BI) are suppressed over much of the wavenumber space, whereas those which are otherwise impeded by field-line convergence/divergence (the MTI) are strengthened. As a result, the wavenumbers at which the HBI survives largely unsuppressed in the ICM have parallel components too small to rigorously be considered local. This is particularly true as the magnetic field becomes more and more orthogonal to the temperature gradient. The field-line insula tion found by recent numerical simulations to be a nonlinear consequence of the standard HBI might therefore be attenuated. In contrast, the fastest-growing MTI modes are unaffected by anisotropic viscosity. However, we