Studies of charged particle populations in the solar wind using Solar Orbiter SWA data.

UCL/MSSL is the Principal Investigator (PI) Institute on an international consortium providing the Solar Wind Analyser suite (SWA) of instruments for the ESA Solar Orbiter mission. Using 3 scientific sensors, 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) and at high solar latitudes. In particular, UCL/MSSL has designed and built the Electron Analyser System (EAS) for the SWA suite. SWA partners in France, Italy and the USA have provided the Heavy Ion Sensor (HIS) and Proton-Alpha Sensor (PAS) for the suite.

The mission is currently baselined for launch in Feb 2020, with a back-up in October 2020. SWA data will be available within a few weeks of the launch, and thus analysis of this new data set can begin within the first year of this PhD program. In particular, we aim to use cruise-phase measurements from the 3 SWA sensors to undertake studies of the nature of the solar wind particle populations, their variability and their links to the Sun. In the (hopefully short) period between the start of the PhD and launch we will undertake background/ preparatory studies using data from previous missions.

Many potential research projects fall within the scope of the mission science plan (as detailed, for example, in the mission 'Science Activity Plan' at https://issues.cosmos.esa.int/solarorbiterwiki/display/SOSP/SAP-related+work generated by the PI's and ESA) and so a specific initial project will be identified at the start of the funded period according to the specific background and interests of the student. As a possible 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 that will be available from SWA EAS. As a further example of the kind of scientific research possible here, the student might undertake studies of both the global drivers and local properties of interplanetary shocks. Shocks and other wave fronts are driven through the solar wind by many forms of solar activity (for example, CME eruption, co-rotating interaction regions). These shock fronts will be captured in unprecedented detail as they pass the spacecraft by the execution of a trigger mode on SWA and other in situ instruments.

The results of such projects are critical to the success of the overall ESA Solar Orbiter program, and the student will thus also be an integral part of the MSSL science and science-planning team. The student will also have the opportunity to collaborate with our partners in France, Italy and the USA, who have provided the HIS and PAS sensors for the SWA suite. This project will place the student in a good position to collaborate more generally and to find future positions e.g. within the Solar Orbiter community internationally.