Kinetic Turbulence and Particle Transport in Astrophysical Plasmas

在天体物理学等离子体中，如太阳风或星际介质湍流已经被观察到。这意味着等离子体中的能量从大尺度级联到小尺度。到目前为止频谱的低频部分（即，低于质子回旋频率）。在这个频率范围内，等离子体湍流可以用磁流体力学理论和Kolmogorov或Goldreich和Sridhar的湍流模型来描述。这种方法的先决条件是流体的plasma.Recent观测在太阳风中所执行的集群和MMS和未来的观测由雷神使命将授予一个更详细的了解湍流质子回旋频率以外。在该范围内，等离子体中的动力学效应变得相关，并且流体描述不再是一种选择。从观测和理论上考虑，还不可能找到一个详细的描述波的模式和结构的动力region.The目前的项目旨在更好地了解这一制度：使用数值模拟，它应调查如何湍流演变在更大的尺度。这里的核心问题是，没有一个单一的模拟技术能够捕捉所有的波数范围。有些方法不能描述每一个区域的物理过程，而另一些方法则需要大量的数值计算，本项目的目的是将不同的方法结合起来，从模拟中得到一个多尺度模型，其范围从MHD湍流到最小的动力学尺度。将使用的技术是MHD模拟、混合和粒子细胞代码。在这个项目中将处理以下问题： 在质子回旋频率之外的湍流的性质是什么？ 动力学湍流对粒子输运（特别是电子）有什么影响？最后一个问题在这个项目中非常重要。粒子输运本身不仅在科学上令人感兴趣，而且在空间天气中的应用也具有技术应用。在这个项目中，将特别关注电子的传输。由于电子共振主要与湍流的动力学制度，应该有一个可观察到的差异质子运输。应研究电子输运是否可用于探测湍流。

In astrophysical plasmas like the solar wind or the interstellar medium turbulence has been observed. This means that energy in the plasma is cascading from large scales to smaller scales. Up to now the low frequency part of the spectrum (i.e., below the proton gyrofrequency) has been considered. In this frequency range plasma turbulence can be described using magnetohydrodynamics theory and the turbulence models by Kolmogorov or Goldreich and Sridhar. A prerequisite for this approach is a fluid description for the plasma.Recent observations in the solar wind as performed by Cluster and MMS and future observations by the THOR mission will grant a more detailed insight into turbulence beyond the proton gyrofrequency. In that range kinetic effect in the plasma become relevant and fluid descriptions are no longer an option. It has not been possible from observations and theoretical considerations to find a detailed description of wave modes and structures presents in the kinetic regime.The current project aims at a better understanding of this regime: Using numerical simulations, it shall be investigated how turbulence evolves over even larger scales. The core problem here is that there is not a single simulation technique capable of capturing all wave number ranges. Some techniques do not describe the physics in every regime, while other would incur a too large numerical effort.The ansatz of this project is to couple different techniques in a way that a multiscale model can be derived from the simulations, which spans a range from MHD turbulence to smallest kinetic scales. The techniques to be used are MHD simulations, hybrid and particle-in-cell codes.The following problems shall be approached in this project:- What is the nature of turbulence beyond the proton gyrofrequency?- Which influence does kinetic turbulence have on the particle transport (especially of electrons)?The last question is very important in this project. Particle transport itself is not only scientifically interesting, but the application to space weather have also technical applications. In this project there will be a special focus on the transport of electrons. Since electrons resonate mostly with turbulence in the kinetic regime, there should be an observable difference to proton transport. It shall be investigated if electron transport can be used to probe turbulence.