Solar Orbiter – Solar Wind Analyser Suite: Design and performance of the Electron Analyser System for the measurement of Solar Wind Electrons

Abstract:

Solar Orbiter, launched in February 2020, will sample the near-Sun (< 0.3 AU) and high helio-latitude (> 30 degrees) environments using a state of the art complement of both in situ and remote sensing instruments. In this contribution, we discuss details of the Electron Analyser System (EAS), one of 3 sensor units which make up the Solar Wind Analyser (SWA) in-situ suite of instruments. EAS consists of two top-hat electrostatic analyser heads, each with a field of view (FOV) of 90° x 360°, mounted orthogonal to each other to provide full sky coverage. The analysers are enhanced performance top-hats with a deflection system enabling electrostatic steering of the incoming particles to cover a ±45° FOV and a variable geometric factor system enabling electrostatic control of particle throughput by up to an order of magnitude. The sensor is additionally mounted at the end of a 4-metre boom, minimising FOV blockage by the spacecraft and its appendages as well as the impact of photo- and secondary-electrons on the low-energy solar wind plasma. Details of the design will be presented along with charged particle optics and ground calibration results and preliminary in-flight performance will be discussed. The instrument has several features for flexible sampling of solar wind electron plasma as well as for monitoring the health of the sensor throughout the life of the mission. These will also be discussed.