Space current sheets: structure, stability and evolution

在宇宙中的热而稀的无碰撞等离子体中，电流片（CS）是累积的磁能通过重连释放的地方，通常是爆炸性的，导致等离子体加热，等离子体体整体流动和粒子加速。因此，CSs是仅次于激波的对天体物理等离子体演化最重要的物理现象，尽管它们与天体物理等离子体的结构、稳定性和演化有关，但许多关键问题仍然没有解决。其中包括离子组成的影响，各向异性和等离子体湍流的作用。原因是大多数天体物理学的CS都无法直接观测。幸运的是，宇宙CS可以在日光层中进行原位研究，例如在行星磁尾和太阳风中。这些研究揭示了由比质子重的离子、粒子速度空间分布的各向异性和湍流引起的多尺度CS结构，并将这些性质深入到最小的电子尺度（地球，火星和水星）和太阳风，利用现有的卫星数据的财富，从统一的角度来看，基于CS结构，稳定性和能量释放的模型，通过他们，我们将开发，考虑到离子的丰度，我们的比较研究考虑到，虽然表征空间等离子体中CS的绝对参数有很大差异，但归一化到等离子体条件下的物理相关量表明类似的物理情况。为此目的，我们将利用多航天器观测地球的磁尾在离子尺度的集群和MMS在电子尺度。为了研究火星磁尾中的CS，我们将使用MAVEN观测，对于Hermean磁尾，我们将使用信使号的观测，对于太阳风中的CS，我们将使用STEREO A和B、WIND、ACE、ULYSSES、HELIOS 1和2、CASSINI、VOYAGER 1和2等太阳层航天器。我们将开发和应用CS结构的分析模型依赖于所观察到的环境条件，研究它们的稳定性理论和数值模拟的手段，探索的不稳定结构的演变，以及通过他们利用测试粒子，混合动力学和PIC代码的数值模拟重连的非线性后果。我们将验证模型预测的多尺度CS结构及其演变的影响下，重离子，各向异性分布函数和湍流的空间观测，以及高能粒子的光谱，为了能够得出结论，也为远程天体物理CS，不能直接访问现场观测。

In the hot and dilute collisionless plasmas of the Universe, current sheets (CSs) are the sites at which accumulated magnetic energy is released, often explosively, by reconnection, causing plasma heating, plasma-bulk-flow and particle acceleration. Hence, CSs are next to shock waves most important for the energization of astrophysical plasmas.Despite their relevance a number of crucial questions about structure, stability and evolution of astrophysical CSs are still unsolved. Among them are the influence of the ion composition, of anisotropies and the role of the plasma turbulence. The reason is that most astrophysical CSs are out-of reach for direct observations. Fortunately, cosmic CSs can be in-situ investigated in the heliosphere, e.g. in planetary magnetotails and in the solar wind. These investigations have revealed multi-scale CS structures due to ions heavier than protons, anisotropies in the particles velocity space distribution and turbulence down to the smallest, the electron scales.We plan systematical analysis of those properties of CS in three planetary magnetotails (Earth, Mars and Mercury) and in the solar wind, utilizing the wealth of existing satellite data from a unified point of view based on models of CS structure, stability and energy release through them, which we are going to develop, taking into account the abundance of ions, heavier than protons, anisotropic distribution functions and turbulence similar to the observed ones.Our comparative investigations take into account that, although the absolute parameters characterizing CSs in space plasmas considerably differ, the physically relevant quantities, normalized to the plasma conditions, indicate similar physical situations. For this purpose we will utilize multi-spacecraft observations in the Earth's magnetotail by CLUSTER at ion scales and by MMS at electron scales. For the investigations of CSs in the Martian magnetotail we will use MAVEN observations, for the Hermean magnetotail those of MESSENGER, for CSs in the solar wind the heliospheric spacecraft STEREO A and B, WIND, ACE, ULYSSES, HELIOS 1 and 2, CASSINI, VOYAGER 1 and 2. We will develop and apply analytical models of CS structure in dependence on the observed environmental conditions, investigate their stability theoretically and by means of numerical simulations, explore the nonlinear consequences of the evolution of the unstable structures as well as of reconnection through them utilizing test-particle, hybrid-kinetic and PIC-code numerical simulations. We will verify the model predictions of multi-scale CS structures and their evolution under the influence of heavy ions, anisotropic distribution functions and turbulence by means of space observations, as well as the spectra of energetic particles, in order to be able to draw conclusions also for remote astrophysical CSs, not directly accessible for in situ observations.