Kinetic theory of small-amplitude fluctuations in astrophysical plasmas
Kinetic theory of small-amplitude fluctuations in astrophysical plasmas
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天体物理等离子体小幅度涨落的动力学理论
DOI：
10.1016/j.physrep.2018.10.003
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Schlickeiser
中科院分区：
文献类型：
--
作者：
Kolberg;Schlickeiser
电磁场涨落可以说是经典无碰撞等离子体中最基本的动力学过程之一。考虑到它们的两个特征，传播和振幅调制，它们包括波和不稳定性等突出现象。这项工作致力于扩展他们的理论理解，特别强调弱传播和非周期性波动及其自发辐射。在这方面，主要取得了三个结果，有助于一般的等离子体理论以及天体物理的应用：第一，弱耦合热等离子体的波动耗散定理推广到任意值的复频率，以摆脱以前的公式在这方面的限制;第二，自发发射的磁场波动在星系际介质中进行了处理。由于最近发现的阻尼和非周期性模式，磁噪声的水平足够高，后者作为种子场进一步放大过程，如磁流体动力发电机行动，所以这种自发辐射是宇宙磁成因的主要相关性。在这里，它表明，一个高度相对论性的电子-正电子对光束可以触发这些阻尼波动到放大的在一定的波数范围内的过渡，从而允许一个更高的种子级。结果表明，只有那些波矢垂直于或几乎垂直于光束传播方向的涨落才能被放大。第三，由于韦伯模的稳定分支至今仍有待于实验证实，因此我们对这一新发现的稳定分支的观测证据进行了研究。结果表明，模式驱动的湍流是不可压缩的，因此，色散措施，旋转措施，和闪烁相关的技术是不适用的。然而，所产生的模式的速度波动，被证明是足够大的资格线加宽的研究作为一个合适的诊断方法来检测模式毕竟。
Electromagnetic field fluctuations are arguably among the most fundamental kinetic processes in classical, collisionless plasmas. Considering their two characteristic features, propagation and amplitude modulation, they include such eminent phenomena as waves and instabilities. This work is devoted to an extension of their theoretical understanding with particular emphasis on weakly propagating and aperiodic fluctuations and their spontaneous emission. In this regard, three main results are achieved that contribute to both generic plasma theory as well as astrophysical applications.Firstly, the fluctuation–dissipation theorem for weakly coupled thermal plasmas is generalized to arbitrary values of the complex frequency in order to rid the previous formulations of their restrictions in this respect.Secondly, the spontaneously emitted magnetic field fluctuations in the intergalactic medium are addressed. Due to a recently discovered damped and aperiodic mode, the level of magnetic noise is high enough to have the latter serving as a seed field for further amplification processes like magnetohydrodynamic dynamo action, so this spontaneous emission is of major relevance for cosmic magnetogenesis. Here, it is shown that a highly relativistic electron–positron pair beam can trigger a transition of these damped fluctuations into amplified ones in certain wavenumber ranges, thus allowing for an even higher seed level. It is found that only those fluctuations are accessible to amplification whose wavevectors are perpendicular or at least almost perpendicular to the propagation direction of the beam.Thirdly, the possibilities are investigated to obtain observational evidence for this newly discovered stable branch of the Weibel mode because an empirical confirmation of its existence is still pending today. It is shown that the mode-driven turbulence is incompressible and that, therefore, dispersion measure, rotation measure, and scintillation related techniques are not applicable. The velocity fluctuations generated by the mode, however, are shown to be large enough to qualify line broadening studies as a suitable diagnostic method to detect the mode after all.
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影响因子：
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