Solar Accelerated Electron Beam-Plasma Interactions in our Solar System

Our Sun's outer atmosphere is extremely unstable. Frequent explosions accelerate particle beams to near-light speeds, and periodically expel huge volumes of mass, known as solar storms. The effect of our active Sun on the Earth is known as space weather. Understanding the acceleration and transport of these particle beams is an important, modern challenge, previously hindered by a lack of spacecraft measurements near the Sun. The goal of this project is to understand how these particle beams evolve on their journey through the solar system using a combined programme of data from cutting-edge spacecraft and advanced simulations.

A new frontier of near-Sun plasma measurements is being taken by NASA's Parker Solar Probe (launched 2018) and ESA's Solar Orbiter (launching 2020), both flying closer to the Sun than ever before. These spacecraft fly through the solar wind, hot plasma that continuously streams out from the Sun and populates the interplanetary space. We will quantify how electron beams resonantly interact with waves in the solar atmosphere and the solar wind. This will involve measuring the time evolution of the near-relativistic electron distribution function at many different distances from the Sun. The particle data can then be compared with increases in local electric fields; the signature of beam-generated plasma waves. The new measurements will allow us to test the validity of existing theories regarding electron energy loss, wave generation, and how both are affected by the turbulent nature of the solar wind. We will then utilise high-performance numerical simulations that model the transport of electrons and their interaction with plasma waves. By including our cutting-edge solar wind data measurements as simulations inputs, we will refine our understanding about how electrons lose energy and change trajectories through the solar system. We will also explore the initial acceleration characteristics in the solar atmosphere, where spacecraft are unable to enter. The new models can make important predictions, including the arrival times of electron beams at Earth. Such outputs can be used to update space weather models that help secure safety for future space technology. This combination of simulations and wide-ranging observations presents an exciting opportunity to significant progress human knowledge and understanding of how the Sun works, and how it interacts with our solar system.