日球层终端激波的全粒子模拟研究

The heliospheric termination shock (TS) is a transition between the solar wind and heliosheath. The found of TS is a milestone in the history of human space exploration. However, there are still many physical problems is remain unclear. As Voyager 2 went across the TS, a single crossing was expected, with a boundary that was stable on a timescale of several days. But the data reveal multiple crossings (at least 5 times) of a complex shock. In addition, observed shock compression ratio and ion heating rate are lower than expected by Rankine-Hugoniot (R-H) jump conditions. Previous observations and one-dimensional simulations indicate that the percentage of pickup ions (PUIs) at the TS is relatively high (about 25%) which may have a large impact on the TS structures. Details are still unclear. To understand the physical problems above, one-and two- dimensional particle-in-cell (PIC) simulations are performed in order to study the particle energy partition and the shock front microstructures of the termination shock. Furthermore, the shock front rippling in small and large scales are investigated to understand the shock front nonstationarity and the multiple crossings of the spacecraft. We concentrate on the full comparison between the Voyager 2 plasma data and the PIC simulation data. This study also may help understand the multiple crossings of the heliopause which is a hot issue nowadays.

日球层终端激波（TS）是太阳风和日鞘层的过渡区，旅行者号飞船对它的发现是人类太空探索史上的一次里程碑。然而，诸多物理问题尚不清楚。旅行者2号穿越终端激波的几天里太阳风非常稳定，科学家们预计穿越只发生1次。但观测表明，飞船至少穿越了激波5次。此外，观测还发现激波压缩率和离子加热率都比用兰金-雨果跃变关系（R-H）预计的值小。前人通过观测和一维模拟指出，终端激波处新生离子（PUIs）百分比较大（约25%），这对终端激波结构会产生很大影响。但具体细节仍不清楚。为了理解上述物理问题，我们利用一维和二维的全粒子模拟（PIC）研究终端激波处的粒子能量分配和激波面微观结构。另外，我们还研究激波面大、小尺度的涟波、理解激波面非稳态的物理机制、解释飞船为什么会多次穿越终端激波。我们重点对旅行者2号的等离子体数据和模拟结果做一次全面的比较。本研究对理解当今热点问题“飞船多次穿越日球层顶”也会起到一定的帮助。

日球层终端激波（TS）是太阳风和日鞘层的过渡区，旅行者号飞船对它的发现是人类太空探索史上的一次里程碑。然而，诸多物理问题尚不清楚。我们利用全粒子模拟研究终端激波处的粒子能量分配和激波面非稳态结构，重点对旅行者2号的等离子体数据和模拟结果做一次全面的比较。本研究不但揭示了飞船多次穿越日球层顶极有可能是激波面的非稳态造成的，同时也得到了粒子从上游到下游的完整演化过程。我们不但完整揭示了旅行者号飞船观测到的日球层终端激波数据，还将模型推广到整个外日球层。模拟结果与新视野号在外日球层观测到的离子能谱和激波特性一致。这充分证明了我们研究方法的普适性。本研究能帮助我们理解日球层结构、太阳高能粒子加速机制以及反常宇宙射线的产生机制。相关研究结果已在国内外SCI期刊上发表论文7篇，并做国际会议邀请报告3次、口头报告多次，协助培养博士生2名。