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arXiv 2106.04787physics.flu-dynastro-ph.HEphysics.plasm-ph
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Rayleigh-Taylor不稳定性中小尺度发电机性质的标度

Scaling of Small-Scale Dynamo Properties in the Rayleigh-Taylor Instability

Valentin Skoutnev, Elias R. Most, Amitava Bhattacharjee, Alexander A. Philippov

摘要:

我们推导出缩放关系的基础上自由落体和各向同性假设的运动小尺度发电机的增长率和放大因子的过程中的混合,饱和和衰减阶段的瑞利-泰勒不稳定性(RTI)在完全电离等离子体。的标度关系进行测试,使用组的三维,粘阻MHD模拟的RTI,并发现保持在饱和阶段,但表现出的差异在混合和衰变阶段,这表明需要放松自由落体或各向同性的假设。应用的标度关系允许在运动发电机阶段的净放大的磁能的定量预测,因此,确定是否的磁能要么保持在所有的速度尺度或达到均分与至少一些尺度的湍流动能在实验室和天体物理的情况下。作为一个例子,我们认为在RTI不稳定区域的外层包络的二进制中子星合并的发电机和预测的小规模发电机的运动学制度结束的纳秒的时间尺度上,然后达到饱和的时间尺度为微秒,这都是快的毫秒弛豫时间的合并后。

英文摘要:

We derive scaling relations based on free-fall and isotropy assumptions for the kinematic small-scale dynamo growth rate and amplification factor over the course of the mixing, saturation, and decay phases of the Rayleigh-Taylor instability (RTI) in a fully-ionized plasma. The scaling relations are tested using sets of three dimensional, visco-resistive MHD simulations of the RTI and found to hold in the saturation phase, but exhibit discrepancies during the mixing and decays phases, suggesting a need to relax either the free-fall or isotropy assumptions. Application of the scaling relations allows for quantitative prediction of the net amplification of magnetic energy in the kinematic dynamo phase and therefore a determination of whether the magnetic energy either remains sub-equipartition at all velocity scales or reaches equipartition with at least some scales of the turbulent kinetic energy in laboratory and astrophysical scenarios. As an example, we consider the dynamo in RTI-unstable regions of the outer envelope of a binary neutron star merger and predict that the kinematic regime of the small-scale dynamo ends on the time scale of nanoseconds and then reaches saturation on a timescale of microseconds, which are both fast compared to the millisecond relaxation time of the post-merger.

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