Ion-scale current sheet instabilities in kinetic plasma turbulence

无碰撞等离子体物理学的一个关键未解决的问题，例如，太阳风和日冕是宏观能量的不可逆耗散，没有碰撞粘性和电阻率。它是通过能量从宏观尺度到动力学尺度的湍流转移而实现的，在动力学尺度能量最终被耗散。现场多航天器（集群，MMS）的空间观测和无碰撞等离子体湍流的数值模拟表明，间歇性耗散本地化和周围的动力学尺度电流片自洽形成的湍流的证据。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确定动力学等离子体湍流的相关性质，例如，磁场谱的离子尺度突变和波矢各向异性的非单调尺度依赖性。然而，动力学尺度电流片不稳定性在决定耗散和湍流性质方面的作用尚不清楚。这个建议的目的是调查离子尺度等离子体不稳定性的作用，这是可能增长的离子动力学等离子体湍流中形成的电流片，在确定的离子尺度的湍流特性，特别是，位置的离子尺度的突破和非单调的尺度依赖波矢量各向异性。首先，我们将使用A.I.K.E.F.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）。TU布伦瑞克的代码，以表征（1）通过变量的功率谱、破裂位置和波矢量各向异性充分发展的3-D湍流，（2）通过其峰值电流密度、厚度、宽度形成的电流片，电子和离子电流的高度和分数以及（3）通过密度的梯度标度长度和离子和电子的体积速度以及离子温度各向异性，这些电流片中的自由能量源。接下来，在个别层流片与自由能源和参数的湍流的电流片的典型的等离子体不稳定性的非线性演化将研究的混合代码模拟初始化与适当的一维电流片平衡。链接，如果有的话，在个别电流片之间的湍流和等离子体不稳定性将探索通过比较的湍流的属性与相应的属性的非线性状态的演变个别电流片。我们的研究在0.1-10的范围内的八个值的离子等离子体β将比较与MMS/CLUSTER观测电流片和湍流与Z。Vörös和Y.在格拉兹的成田机场。我们的研究是及时的，因为专门的磁重联，电流片和湍流的动力学尺度测量将由MMS空间使命和实验室实验VINETA-II在格赖夫斯瓦尔德和FLARE在普林斯顿从2018年开始。

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.