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

由于太阳风的磁场很弱，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，并导致了高能粒子的产生。1974年和1975年，Short Mariner 10号航天器首次对Herean磁场、等离子体和粒子环境进行了现场观测。在水星附近已经发现了能量超过60keV的电子和能量超过80keV的质子，远远高于上游太阳风(1.5-10keV)中的粒子能量。由于水星上的粒子加速机制是一个尚未解决的奇迹，人们已经提出了几种机制来解释观测到的高粒子能量，例如Herean磁尾中的重联和Herean弓形激波处的加速、随机Ist和二阶费米加速。由于水星的空间尺度较小，而拉莫尔半径较大，并且由于加速度的时间尺度较短，要正确描述水星上的粒子加速，需要等离子体动力学方法。在这个方案中，我们主要关注由于磁尾重联和激波加速而引起的粒子加速的动力学模拟。以前对赫平均粒子加速的研究通常是基于给定磁场和电场下的测试粒子计算，该计算来自于修正的地球磁场经验模型。相比之下，我们将从基于NASA信使号宇宙飞船2011年后刚刚观测到的、目前正在开发的赫米恩磁场模型开始，例如在MPS Lindau发电机小组中。对于无碰撞磁尾等离子体中的加速，我们将模拟向下变薄到离子惯性长度的尾部电流片。在它们中，加速电场的形成是一个纯粹的动力学过程，我们将相应地处理。由于电子和离子的去耦合，动力学重联速率(电场)高于流体重联模型。早期的Herean弓形激波粒子加速模型发现，对于MHD跳跃条件，无法解释观测到的高能。目前对行星弓激波的观测表明，它们可能变得非常薄，大约是几个电子惯性长度(c/cope)，因此是离子惯性长度(c/o)的一小部分)，因此必须考虑动力学效应才能理解激波加速。虽然对于地球来说，离子加速也被发现是由于前震等离子体“气泡”中的相互作用，但它们的存在对于水星来说仍有待证明。到目前为止，它们中的粒子加速只能通过混合模拟来处理，在混合模拟中，只有离子被动力学处理，而电子äS是一种无质量的流体。由于水星的Alfven马赫数(MA~40)远大于地球的马赫数(MA&lt；10)，激波和前震粒子加速的条件将不同于其他行星冲击波。因此，我们建议对水星的两个假定粒子加速点，Herean磁尾及其激波区域，完全动量地处理。我们计划首先使用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3D PIC模拟代码。

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.