标题： 彗星67P的离子动力学：与罗塞塔数据比较的碰撞粒子方法 显示英文标题

标题： Cometary ion dynamics at 67P: A collisional test-particle approach with Rosetta data comparison

摘要： 罗塞塔航天器陪伴彗星67P/丘留莫夫-格拉西缅科两年，收集了丰富且多变的数据集。 在罗塞塔等离子体联盟（RPC）仪器的数据中，包括通过互阻抗探针（MIP）和朗缪尔探针（LAP）测量的总电子密度。 在低挥发性条件下，等离子体密度测量可以通过电离产生的平衡和通过传输损失的平衡来解释。 假设离子以中性气体的流出速度沿径向运动。 在近日点附近，这种无磁场无化学反应的模型假设不再有效，等离子体密度被高估。 这可以由磁异常腔体内由于双极电场增强的离子传输来解释，太阳风磁场无法到达该区域。 在本研究中，我们探讨了这两个模式之间的过渡，在中等挥发性（$5.4 \times10^{26}~\mathrm{s^{-1}}$）时，当彗星和太阳风等离子体之间的相互作用影响离子的传输。 我们使用了一个3D碰撞测试粒子模型，改编自Stephenson等人2022年的研究，用于模拟2.5-3天文单位处的彗星离子，输入电场和磁场来自混合模拟。 然后将该模型的总等离子体密度与MIP/LAP的数据以及无磁场无化学反应的模型进行比较。 在此过程中，我们突出了混合方法的局限性，并展示了对电子碰撞冷却进行建模的重要性，以理解靠近核附近的离子动力学。 显示英文摘要

摘要： The Rosetta spacecraft escorted comet 67P/Churyumov-Gerasimenko for two years, gathering a rich and variable dataset. Amongst the data from the Rosetta Plasma Consortium (RPC) suite of instruments are measurements of the total electron density from the Mutual Impedance Probe (MIP) and Langmuir Probe (LAP). At low outgassing, the plasma density measurements can be explained by a simple balance between the production through ionisation and loss through transport. Ions are assumed to travel radially at the outflow speed of the neutral gas. Near perihelion, the assumptions of this field-free chemistry-free model are no longer valid, and plasma density is overestimated. This can be explained by enhanced ion transport by an ambipolar electric field inside the diamagnetic cavity, where the interplanetary magnetic field does not reach. In this study, we explore the transition between these two regimes, at intermediate outgassing ($5.4 \times10^{26}~\mathrm{s^{-1}}$), when the interaction between the cometary and solar wind plasma influences the transport of the ions. We use a 3D collisional test-particle model, adapted from Stephenson et al. 2022 to model the cometary ions with input electric and magnetic fields from a hybrid simulation for 2.5-3 au. The total plasma density from this model is then compared to data from MIP/LAP and to the field-free chemistry-free model. In doing so, we highlight the limitations of the hybrid approach and demonstrate the importance of modelling collisional cooling of the electrons to understand the ion dynamics close to the nucleus.