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

UCL/MSSL是一个国际财团的主要研究所，为定于2018年发射的欧空局太阳轨道器使命提供太阳风分析仪套件（SWA）。SWA将在距离太阳0.28 Au（即太阳到地球距离的四分之一左右）的不同距离处对电子、质子、α粒子和重离子群进行采样。特别是，UCL/MSSL正在为SWA套件设计和建造电子分析仪系统（EAS）。为了准备这一使命，并能够利用这三个传感器对太阳风进行最佳测量，我们将利用现有在轨飞行任务的相关数据，对太阳风粒子群的性质、其可变性及其与太阳的联系进行研究。最冷电子的“核心”人口几乎是各向同性的-在任何方向上都可以检测到给定能量的电子的大致相同的通量;“晕”人口出现在稍微更高的能量处，并且相对于核心显示出平均速度的轻微变化，因此在太阳风中提供了“热通量”;最后，一个“strahl”人口往往被视为一个更有活力的粒子束流沿着磁场。这些不同的电子群包含了有关太阳源区发生的过程、采样等离子体与太阳的磁连接以及可能发生在太阳风本身内的等离子体过程（例如湍流、波粒相互作用和磁重连）的信息。分离这些过程的影响是一项复杂的任务，需要高节奏，高分辨率的数据类型，在爆发模式期间，当一个或多个航天器位于太阳风中时，由UCL/MSSL建造的PEACE电子能谱仪在4 Cluster航天器上提供。例如，一个与任务高度相关的博士项目将利用这些数据探索电子总数的性质和可变性，利用多点测量来确定航天器之间的变化水平。在SWA离子成分测量和太阳遥感测量之间建立这种联系，已被确定为太阳轨道器使命成功的关键。因此，利用现有数据集建立一种可靠的方法来做到这一点，在发射后分析阶段将是非常宝贵的。这类项目将得益于与伦敦大学学院/海洋和大气科学部太阳物理小组研究人员的合作，该小组拥有遥感观测分析方面的专门知识，这类项目的结果对于欧空局太阳轨道器方案的准备和投入至关重要，因此，学生也将成为海洋和大气科学部科学规划小组的一个组成部分，负责为这些进程提供科学投入。我们还将有机会与法国、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.