Solar Wind Analyser – Electron Analyser System (SWA-EAS) Response Model: An Analysis Tool for the Solar Wind Electron Observations by Solar Orbiter

Abstract:

The Solar Wind Analyser – Electron Analyser System (SWA-EAS) is designed to measure the solar wind electrons in the heliocentric distance range between ~0.3 au and 1 au. The measurements allow the construction and the study of the electron velocity distribution functions (VDFs) which are essential in understanding the solar wind dynamics. SWA-EAS instrument comprises two electrostatic analyser heads with aperture deflectors, orthogonally mounted on a long boom behind the shadow of the spacecraft. The combined field of view from each SWA-EAS unit covers the entire sky and while operating in normal mode, the instrument samples the three dimensional electron VDFs. In burst mode, one of the two analyser units covers the two-dimensional pitch angle distributions of the solar wind electrons allowing the study of basic plasma mechanisms along and perpendicular to the magnetic field direction. In this presentation, we demonstrate a forward model of the instrument’s response which predicts the observations in given solar wind conditions. We use the response model to validate the transformation of the constructed VDFs onto the spacecraft frame and quantify the accuracy of analysis tools that derive the solar wind electron bulk parameters. We specifically examine the accuracy of the statistical velocity moments of the constructed VDFs in certain solar wind conditions. We then investigate whether analytical expressions can be fitted to the observations in order to determine the key populations of solar wind electrons.