Preparing for the Solar Orbiter Mission: Properties of Solar Wind Charged Particle Populations

UCL/MSSL是一个国际联盟的主要研究机构，该联盟为欧洲航天局太阳轨道飞行器任务提供太阳风分析仪套件（SWA），该任务将于2018年发射。SWA将在距离太阳0.28天文单位（即大约太阳到地球距离的四分之一）的不同距离取样电子、质子、α粒子和重离子种群。特别是，UCL/MSSL正在为SWA套件设计和构建电子分析仪系统（EAS）。为了准备任务，并能够使用3个传感器在太阳风中进行最佳测量，我们将利用现有在轨任务的相关数据，研究太阳风粒子群的性质、它们的可变性以及它们与太阳的联系。例如，众所周知，太阳风电子种群一般由3个部分组成：最冷电子的“核心”种群几乎是各向同性的-在任何方向都可以检测到给定能量的大约相同的电子通量；“光晕”人口出现在更高的能量上，并且显示相对于核心的平均速度略有变化，因此在太阳风中提供了“热通量”；最后，“斯特劳”种群通常被视为沿磁场流动的高能粒子束。总之，这些不同的电子居群包含了在太阳源区域发生的过程的信息，采样等离子体与太阳的磁连接，以及可能在太阳风本身发生的等离子体过程（例如湍流、波粒相互作用和磁重联）。分离这些过程的影响是一项复杂的任务，当一个或多个航天器位于太阳风中时，需要从UCL/ mssl建造的4个群集航天器上的PEACE电子能谱仪获得在突发模式期间可用的高节奏，高分辨率数据。例如，一个与任务高度相关的博士项目将使用这些数据来探索电子种群的性质和可变性，使用多点测量来确定航天器之间的变化水平。第二个与任务相关的项目将解决太阳风中的重离子测量与紫外线成像和光谱望远镜对太阳本身的测量之间的联系。在SWA对离子组成的测量和对太阳的遥感测量之间建立这种联系已被确定为太阳轨道飞行器任务成功的关键。因此，利用现有的数据集，建立一个可靠的方法来做这件事，在发射后的分析阶段将是无价的。这样一个项目将受益于与UCL/MSSL太阳物理小组的研究人员的现成合作，该小组拥有分析遥感观测的专业知识。这些项目的结果对于欧空局太阳轨道飞行器计划的准备和投入至关重要，因此学生也将成为MSSL科学规划团队的组成部分，负责为这些过程提供科学投入。我们还将有机会与我们在法国、意大利和美国的合作伙伴合作，他们将为SWA套件提供重离子传感器和质子α传感器。

UCL/MSSL is the Principal Investigator Institute on an international consortium providing the Solar Wind Analyser suite (SWA) of instruments for the ESA Solar Orbiter mission, due for launch in 2018. SWA will sample electron, proton, alpha particle and heavy ion populations at various distances down to 0.28 AU from the Sun (i.e. around a quarter the distance from the Sun to the Earth). In particular, UCL/MSSL is designing and building the electron analyser system (EAS) for the SWA suite. In order to prepare for the mission, and to be able to use the 3 sensors to make optimum measurements in the solar wind, we will undertake studies of the nature of the solar wind particle populations, their variability and their links to the Sun using, where relevant, data from existing in-orbit missions.For example, it is known that the solar wind electron population in general consists of 3 components: A 'core' population of the coldest electrons which is nearly isotropic - approximately the same flux of electrons of a given energy may be detected in any direction; A 'halo' population occurs at somewhat higher energies, and shows a slight shift in average velocity with respect to the core, and thus provides a 'heat flux' in the solar wind; Finally, a 'strahl' population is often seen as a more energetic beam of particles streaming along the magnetic field. Together these different electron populations contain information about the processes occurring at the source region on the Sun, the magnetic connections of the sampled plasma back to the Sun and on the plasma processes (e.g. turbulence, wave-particle interactions and magnetic reconnection) which may be occurring within the solar wind itself. Separating the effects of these processes is a complicated task requiring high-cadence, high resolution data of the type available during burst modes from the UCL/MSSL-built PEACE electron spectrometers on the 4 Cluster spacecraft when one or more of the spacecraft are located in the solar wind. A highly mission-relevant PhD project would, for example, use these data to explore the nature and variability of the electron populations, using the multi-point measurements to determine the level of variation between spacecraft.A second mission-relevant project will address the links between the heavy ion measurements in the solar wind and the measurements of the Sun itself available from ultra-violet imaging and spectroscopic telescopes. Establishing such links between the SWA measurements of ion composition and the remote sensing measurements of the Sun has been identified as critical for the success of the Solar Orbiter mission. Thus establishing a reliable method to do this, with existing datasets, will be invaluable during the post-launch analysis phase. Such a project would benefit from the ready collaboration possible with researchers in the UCL/MSSL Solar Physics Group which possesses expertise in analysis of the remotely sensed observations.The results of such projects are critical as preparation and inputs into the ESA Solar Orbiter program, and the student will thus also be an integral part of the MSSL science-planning team, with the responsibility of making scientific inputs to those processes. There will also be opportunity to collaborate with our partners in France, Italy and the USA, who will provide the Heavy Ion Sensor and Proton-Alpha Sensor for the SWA suite.