Solar Orbiter – Solar Wind Analyser (SWA) Suite: Early results from the Electron Analyser System

Abstract:

Solar Orbiter was launched in early 2020 carrying a state of the art complement of both in situ and remote sensing instruments with a goal to further our understanding of the Sun and its connections to the heliosphere. The spacecraft entered cruise phase on 14^th June 2020, a period during which only the 4 in situ instruments sampling the solar wind around the spacecraft will remain routinely turned on. However, together these sensors can provide new insights into the nature of the solar wind inside 1 AU ahead of the start of the nominal science mission. Of particular focus in this presentation are the early measurements from the Electron Analyser System (EAS), which is one of 3 sensor units which make up the Solar Wind Analyser (SWA) instrument suite. EAS is a dual-head, top-hat electrostatic analyser system that is capable of making 3D measurements of solar wind electrons at energies below ~5 keV from a vantage point at the end of a 4-metre boom extending into the shadow of the spacecraft. This accommodation also helps to minimise the effect of spacecraft related disturbances on the low-energy (less than a few tens of eV) electrons expected the core population of the solar wind.

In this contribution, we illustrate the capabilities of the sensor through presentation of scientific analyses of the early cruise phase measurements from SWA/EAS. We describe how these measurements, including 3D electron velocity distribution functions, moments of the distribution and high time resolution 2D pitch angle distributions, contribute new information for use in answering some open science questions on the nature and origins of the solar wind inside of 1 AU. We also describe the caveats to the availability and accuracy of these measurements and the plans in place to mitigate them.