Ion-scale current sheet instabilities in kinetic plasma turbulence

动态等离子体湍流中的离子级电流片不稳定性

• 批准号: 399153660
• 负责人: Dr. Neeraj Jain
• 金额: --
• 依托单位: Max-Planck-Institut für Sonnensystemforschung (MPS)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/399153660?language=en
• 关键词: Ion; scale; current; sheet; instabilities

A key unsolved problem of the physics of collisionless plasmas, e.g., solar wind and solar corona, is the irreversible dissipation of macroscopic energy without collisional viscosity and electrical resistivity. It is enabled by turbulent transfer of energy from macroscopic to kinetic scales where the energy is finally dissipated. In-situ multi-spacecraft (Cluster, MMS) space observations and numerical simulations of collisionless plasma turbulence show evidences of intermittent dissipation localized in and around kinetic scale current sheets self-consistently formed in the turbulence. Plasma instabilities in these current sheets can provide the collisionless dissipation and determine the associated properties of kinetic plasma turbulence, e.g., the ion-scale break in magnetic field spectra and non-monotonous scale dependence of wave-vector anisotropy. Role of kinetic scale current sheet instabilities in determining the dissipation and the turbulence properties is, however, not clear yet. Goal of this proposal is to investigate the role of ion-scale plasma instabilities, which are likely to grow in current sheets formed in ion kinetic plasma turbulence, in determining the ion-scale properties of the turbulence, in particular, location of the ion-scale break and non-monotonous scale dependence of wave-vector anisotropy. First, we will carry out 3-D hybrid simulations (ions as particles and electrons as inertia-less fluid) of ion-kinetic plasma turbulence using the A.I.K.E.F. code of the TU Braunschweig to characterize (1) the fully developed 3-D turbulence by power spectra of variables, location of the break and wave-vector anisotropy, (2) the current sheets formed thereof by their peak current density, thicknesses, widths, heights and fractions of electron and ion currents and (3) free energy sources in these current sheets by gradient scale lengths of density and ions and electrons bulk velocities and ion temperature anisotropy. Next, nonlinear evolution of plasma instabilities in individual laminar current sheets with free energy sources and parameters typical of the current sheets of the turbulence will be studied by the hybrid code simulations initialized with appropriate one dimensional current sheet equilibria. Links, if any, between the turbulence and plasma instabilities in individual current sheets will be explored by comparing the properties of the turbulence with the corresponding properties of the nonlinear state of the evolution of individual current sheets. Our studies for eight values of ion plasma beta in the range 0.1-10 will be compared with MMS/CLUSTER observations of current sheets and turbulence in collaboration with the group of Z. Vörös and Y. Narita at Graz. Our studies are just timely since dedicated kinetic scale measurements of magnetic reconnection, current sheets and turbulence will be carried out by the MMS space mission and by laboratory experiments VINETA-II at Greifswald and FLARE at Princeton starting 2018.

无碰撞等离子体(如太阳风和日冕)物理中尚未解决的一个关键问题是宏观能量的不可逆耗散，而没有碰撞粘性和电阻率。它是通过能量从宏观到运动尺度的湍流转移而实现的，在那里能量最终被耗散。无碰撞等离子体湍流的多航天器(星团，MMS)原位空间观测和数值模拟表明，在湍流中自洽形成的运动尺度电流片及其周围存在间歇耗散的证据。这些电流片中的等离子体不稳定性可以提供无碰撞耗散，并决定动态等离子体湍流的相关性质，例如，磁场光谱中的离子尺度破裂和波矢各向异性的非单调尺度依赖关系。然而，动力学尺度电流片不稳定性在决定耗散和湍流性质中的作用尚不清楚。这一建议的目的是研究离子尺度等离子体不稳定性在决定湍流的离子尺度性质中的作用，特别是离子尺度破裂的位置和波矢各向异性的非单调尺度依赖关系。离子尺度等离子体不稳定性可能在离子动能等离子体湍流形成的电流片中增长。首先，我们将使用TU Braunschweig的A.I.K.E.F.程序对离子动力学等离子体湍流进行三维混合模拟(离子作为粒子，电子作为无惯性流体)，以表征(1)由变量功率谱、破裂位置和波矢量各向异性充分发展的三维湍流，(2)由其峰值电流密度、厚度、宽度、高度和电子和离子电流的比例形成的电流片，以及(3)这些电流片中的自由能源，由密度和离子的梯度尺度长度和离子和电子的体积速度和离子温度各向异性。接下来，我们将用一维电流片平衡初始化的混合程序模拟，研究具有自由能源和湍流电流片的典型参数的单个层流电流片中等离子体不稳定性的非线性演化。通过比较湍流的性质和单个电流片演化的非线性状态的相应性质，将探索单个电流片中的湍流和等离子体不稳定性之间的联系。我们对0.1-10范围内的8个离子等离子体β的研究将与GRAZ的Z·VöröS和Y·Narita的电流片和湍流的MMS/星团观测相比较。我们的研究来得正是时候，因为从2018年开始，MMS太空任务将对磁重联、电流片和湍流进行专门的动力学尺度测量，格雷夫斯瓦尔德的Vineta-II和普林斯顿的耀斑将通过实验室实验进行。