Kinetic simulation of particle acceleration due to the Interaction of the Mercury magnetic field with the Solar wind

水星磁场与太阳风相互作用引起的粒子加速的动力学模拟

• 批准号: 237376584
• 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: Priority Programmes
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/237376584?language=en
• 关键词: Kinetic; simulation; particle; acceleration; due

Due to the weak Hermean magnetic field and the close distance to the Sun the Solar wind interacts almost directly with almost all of Mercury's cross-section. This forms the most dynamic magnetosphere of all terrestrial planet and causes the generation of highly energetic particles. The Hermean magnetic field, plasma and particle environment was in situ investigated first by short Mariner 10 spacecraft flybys in 1974 and 1975. That already electrons with energies above 60 keV and protons with energies above 80 keV were discovered near Mercury, much above the particle energies in the upstream solar wind (1.5-10 keV). Since than the particle acceleration mechanism at Mercury is an unsolved miracle.Several mechanisms have been proposed to explain the observed high particle energies, e.g. reconnection in the Hermean magnetotail and acceleration at the Hermean bow shock wave, stochastic Ist and 2nd order Fermi acceleration. Due to the small spatial scales at Mercury compared to large Larmor radii and due to the short time scales of acceleration a proper description of the particle acceleration at Mercury requires a plasma kinetic approach. In this proposal we focus on the kinetic Simulation of particle acceleration due to reconnection in the Hermean magnetotail and shock acceleration.Previous investigations of Hermean particle acceleration were usually based on test particle calculations in prescribed magnetic and electric fields taken from a modified empirical models of the external Earth's magnetic field. In contrast we will start with Hermean magnetic fields models based on NASA's Messenger spacecraft observations just made after 2011 and currently under development, e.g. in the MPS Lindau dynamo group. For acceleration in the collisionless Hermean magnetotail plasma we will simulate the tail current sheets thinning down to the ion inertial length. In them the formation of the accelerating electric fields is a purely kinetic process, which we will treat accordingly. Due to the decoupling of electrons and ions the kinetic reconnection rate (electric field) is higher than for fluid (MHD) reconnection models.Already early models of Hermean bow shock particle acceleration models found that for the MHD Jump conditions the observed high energies cannot be explained. Current observations planetary bow shock waves have shown that they might become very thin, about a few electron inertial lengths (c/cope) and, therefore, a fraction of ion inertial length (c/o)pj) so that kinetic effects have to be considered to understand shock acceleration as well. While for the Earth's case ion acceleration was found to be also due to interactions in foreshock plasma "bubbles" their existence has still to be proven for the Mercury. Particle acceleration in them was so far treated only by hybrid simulations in which only the ions are treated kinetically and electrons äs a mass-less fluid. Since at Mercury the Alfven Mach number (MA~40) is much higher than for the Earth (MA<10) the conditions for shock and foreshock particle acceleration will be different from that at the other planetary shock waves.Hence we propose to treat the two assumed particle acceleration sites at Mercury, the Hermean magnetotail and its shock wave regions, fully kinetically. We plan to use first a 2D PIC code which we recently successfully applied to solar particle acceleration. In the course of the project we will apply also a massively parallelized 3D PIC Simulation code, developed in our group together with the Czech Academy of Sciences.

由于赫米亚磁场较弱且距太阳较近，太阳风几乎直接与水星的整个横截面相互作用，这形成了所有类地行星中最具活力的磁层，并导致高能粒子的产生。 1974 年和 1975 年，水手 10 号航天器短暂飞越，首先对等离子体和粒子环境进行了原位研究。其中已经有能量高于 60 keV 的电子和能量高于 60 keV 的质子在水星附近发现了 80 keV，远高于上游太阳风中的粒子能量（1.5-10 keV），因为水星的粒子加速机制是一个未解决的奇迹。已经提出了几种机制来解释观察到的高粒子能量，例如，赫米亚磁尾的重联和赫米亚弓激波的加速、随机 Ist 和二阶费米加速度，因为与大拉莫尔相比，水星的空间尺度较小。半径，并且由于加速的时间尺度短，对水星粒子加速度的正确描述需要等离子体动力学方法。在本提案中，我们重点关注由于赫尔米亚磁尾重联和冲击加速度而产生的粒子加速度的动力学模拟。 Hermean 粒子加速度的计算通常基于在规定的磁场和电场中进行的测试粒子计算，这些磁场和电场取自外部地球磁场的修改经验模型，相反，我们将从基于 NASA 信使号航天器的 Hermean 磁场模型开始。 2011 年之后刚刚进行的观测，目前正在开发中，例如，对于无碰撞 Hermean 磁尾等离子体中的加速，我们将模拟细化至离子惯性长度的尾电流片在其中形成的加速电场。是一个纯粹的动力学过程，我们将相应地处理，由于电子和离子的解耦，动力学重联率（电场）高于流体（MHD）。赫米亚弓激波粒子加速模型的早期模型已经发现，对于 MHD 跳跃条件，观测到的高能量无法解释，当前观测的行星弓激波可能会变得非常薄，约为几个电子惯性长度（ c/cope），因此，离子惯性长度（c/o）pj）的一小部分，因此必须考虑动力学效应来理解冲击加速度，而对于地球的情况，离子加速也被发现是由于。对于前震等离子体“气泡”中的相互作用，它们的存在仍有待证明，因为迄今为止，仅通过混合模拟来处理其中的粒子加速，其中仅对离子进行动力学处理，而电子则作为无质量流体。水星的阿尔文马赫数（MA~40）远高于地球（MA<10），冲击波和前震粒子加速的条件将与其他行星冲击波不同。因此我们建议将水星的两个假设的粒子加速点，赫尔米亚磁尾及其冲击波区域，完全动力学我们计划首先使用我们最近成功应用于太阳粒子加速的二维 PIC 代码。大规模并行 3D PIC 仿真代码，由我们团队与捷克科学院共同开发。