Space current sheets: structure, stability and evolution

空间电流片：结构、稳定性和演化

• 批准号: 426192610
• 负责人: Professor Dr. Jörg Büchner
• 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
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/426192610?language=en
• 关键词: Space; current; sheets; structure; stability

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.

在宇宙的热且稀的无碰撞等离子体中，电流片（CS）是累积磁能通过重新连接释放的场所，通常是爆炸性的，导致等离子体加热、等离子体整体流动和粒子加速。因此，CS对于天体物理等离子体的激发来说是仅次于冲击波的最重要的。尽管它们具有相关性，但有关天体物理CS的结构、稳定性和演化的许多关键问题仍未得到解决。其中包括离子组成、各向异性的影响以及等离子体湍流的作用。原因是大多数天体物理 CS 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。这些研究揭示了由于比质子重的离子、粒子速度空间分布的各向异性以及最小到电子尺度的湍流而产生的多尺度CS结构。我们计划系统分析三个行星磁尾（地球、火星和水星）和太阳风，从统一的角度利用大量现有卫星数据，基于 CS 结构、稳定性和通过它们释放的能量模型，我们将开发这些数据，考虑到考虑了比质子重的离子丰度、各向异性分布函数和与观察到的相似的湍流。我们的比较研究考虑到，尽管表征空间等离子体中CS的绝对参数有很大差异，但物理相关量（标准化为等离子体）条件，表示相似的身体状况。为此，我们将利用离子尺度的 CLUSTER 和电子尺度的 MMS 对地球磁尾进行多航天器观测。对于火星磁尾中的 CS 的研究，我们将使用 MAVEN 观测，对于 Hermean 磁尾，我们将使用 MESSENGER 的观测，对于太阳风中的 CS，我们将使用日光层航天器 STEREO A 和 B、WIND、ACE、ULYSSES、HELIOS 1 和 2、CASSINI、航行者 1 号和 2 号。我们将根据观测到的环境条件开发和应用 CS 结构的分析模型，从理论上研究其稳定性并通过数值模拟，利用测试粒子、混合动力学和 PIC 代码数值模拟，探索不稳定结构演化以及重新连接的非线性后果。我们将通过空间观测以及高能粒子光谱来验证重离子、各向异性分布函数和湍流影响下的多尺度CS结构及其演化的模型预测，以便能够得出结论也适用于无法直接进行现场观测的远程天体物理观测站。