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.

由于水星的磁场很弱，而且距离太阳很近，太阳风几乎直接与水星的几乎所有横截面相互作用。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号航天器首次对Hermean磁场、等离子体和粒子环境进行了短暂的实地调查。在水星附近已经发现了能量超过60 keV的电子和能量超过80 keV的质子，远高于上游太阳风中的粒子能量（1.5-10 keV）。由于水星上的粒子加速机制是一个未解的奇迹，人们提出了几种机制来解释观测到的高粒子能量，例如Hermean磁尾的重联和Hermean弓形激波的加速，随机的Ist和二阶费米加速。由于小的空间尺度在水星相比，大拉莫尔半径和由于短的时间尺度的加速粒子加速在水星的适当描述需要一个等离子体动力学的方法。本文主要研究了Hermean磁尾重联和激波加速引起的粒子加速的动力学模拟，以往的Hermean粒子加速的研究通常是基于实验粒子在指定磁场和电场中的计算，而这些磁场和电场是根据修正的地球外部磁场的经验模型得出的。相比之下，我们将从Hermean磁场模型开始，该模型基于2011年后刚刚进行的NASA信使号航天器观测，目前正在开发中，例如MPS Lindau发电机组。对于加速在无碰撞的赫敏磁尾等离子体，我们将模拟尾电流片减薄到离子惯性长度。在它们中，加速电场的形成是一个纯粹的动力学过程，我们将相应地加以论述。由于电子和离子的退耦，动力学重联率（电场）高于流体（MHD）重联模型。早期的Hermean弓形激波粒子加速模型发现，对于MHD跳跃条件，观测到的高能量无法解释。目前对行星弓形激波的观测表明，它们可能会变得非常薄，大约只有几个电子惯性长度（c/科普），因此，只有离子惯性长度（c/o）的一小部分，因此，为了理解激波加速，也必须考虑动力学效应。虽然对于地球的情况下，离子加速被发现也是由于前震等离子体“气泡”的相互作用，但它们的存在仍有待证明。到目前为止，它们中的粒子加速仅通过混合模拟来处理，其中仅离子被动力学处理，电子是无质量流体。由于水星的阿尔芬马赫数（MA~40）远高于地球（MA<10），因此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，我们建议完全动力学地处理水星上的两个假设粒子加速点，即赫敏磁尾及其冲击波区域。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。在项目过程中，我们还将应用我们与捷克科学院共同开发的大规模并行化3D PIC模拟代码。