Energy Distribution of Pickup Ions at the Solar Wind Termination Shock
Energy Distribution of Pickup Ions at the Solar Wind Termination Shock
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DOI：
10.3847/1538-4357/aabf96
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发表时间：
2018-06
期刊：
影响因子：
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通讯作者：
Rahul Kumar;E. Zirnstein;A. Spitkovsky
中科院分区：
文献类型：
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作者：
Rahul Kumar;E. Zirnstein;A. Spitkovsky
旅行者2号航天器进行的现场测量表明，太阳风终止激波受到由于星际中性粒子和太阳风离子之间的电荷交换而在内日光层产生的拾取离子的显著影响。我们使用一个完全动力学的粒子在细胞的方法来自洽地模拟冲击与旅行者2号提供的所有物理特性。我们已经进行了一组模拟与不同的速度分布函数的皮卡离子，因为它不是由旅行者的测量。我们表明，测量表明，上游的冲击皮卡离子比通常认为的更有活力。如果它们的速度分布函数在风系中假设为填充壳形状，那么拾取离子的最大截止速度应该是650 km s-1，以便重现测量结果，这几乎是当地风速的两倍。我们认为，皮卡离子上游的冲击是充满活力的绝热压缩的太阳风等离子体，以及由于在一个广泛的前震区域的湍流增强水平。
In-situ measurements taken by the Voyager 2 spacecraft suggest that the solar wind termination shock is significantly affected by the presence of pickup ions that are produced in the inner heliosphere due to charge exchange between interstellar neutrals and the solar wind ions. We use a fully kinetic particle-in-cell method to self-consistently simulate the shock with all physical properties available from Voyager 2. We have performed a set of simulations with varying velocity distribution functions for the pickup ions, since it was not determined by Voyager’s measurements. We show that the measurements suggest that the pickup ions upstream of the shock are more energetic than generally believed. If their velocity distribution function assumes a filled-shell shape in the wind frame, the maximum cutoff speed for the pickup ions should be ≳650 km s−1 in order to reproduce the measurements, which is almost twice the local wind speed. We suggest that pickup ions upstream of the shock are energized by adiabatic compression of the solar wind plasma as well as due to an enhanced level of turbulence in a broad foreshock region.