The Solar Orbiter Solar Wind Analyser (SWA) suite

Abstract

The Solar Orbiter mission seeks to make connections between the physical processes occurring at the Sun or in the solar corona and the nature of the solar wind created by those processes which is subsequently observed at the spacecraft. The mission also targets physical processes occurring in the solar wind itself during its journey from its source to the spacecraft. To meet the specific mission science goals, Solar Orbiter will be equipped with both remote-sensing and in-situ instruments which will make unprecedented measurements of the solar atmosphere and the inner heliosphere. A crucial set of measurements will be provided by the Solar Wind Analyser (SWA) suite of instruments. This suite consists of an Electron Analyser System (SWA-EAS), a Proton and Alpha particle Sensor (SWA-PAS), and a Heavy Ion Sensor (SWA-HIS) which are jointly served by a central control and data processing unit (SWA-DPU). Together these sensors will measure and categorise the vast majority of thermal and suprathermal ions and electrons in the solar wind and determine the abundances and charge states of the heavy ion populations. The three sensors in the SWA suite are each based on the top hat electrostatic analyser concept, which has been deployed on numerous space plasma missions. The SWA-EAS uses two such heads, each of which have 360° azimuth acceptance angles and ±45° aperture deflection plates. Together these two sensors, which are mounted on the end of the boom, will cover a full sky field-of-view (FoV) (except for blockages by the spacecraft and its appendages) and measure the full 3D velocity distribution function (VDF) of solar wind electrons in the energy range of a few eV to ∼5 keV. The SWA-PAS instrument also uses an electrostatic analyser with a more confined FoV (−24° to +42° × ±22.5° around the expected solar wind arrival direction), which nevertheless is capable of measuring the full 3D VDF of the protons and alpha particles arriving at the instrument in the energy range from 200 eV/q to 20 keV/e. Finally, SWA-HIS measures the composition and 3D VDFs of heavy ions in the bulk solar wind as well as those of the major constituents in the suprathermal energy range and those of pick-up ions. The sensor resolves the full 3D VDFs of the prominent heavy ions at a resolution of 5 min in normal mode and 30 s in burst mode. Additionally, SWA-HIS measures 3D VDFs of alpha particles at a 4 s resolution in burst mode. Measurements are over a FoV of −33° to +66° × ±20° around the expected solar wind arrival direction and at energies up to 80 keV/e. The mass resolution (m/Δm) is > 5. This paper describes how the three SWA scientific sensors, as delivered to the spacecraft, meet or exceed the performance requirements originally set out to achieve the mission’s science goals. We describe the motivation and specific requirements for each of the three sensors within the SWA suite, their expected science results, their main characteristics, and their operation through the central SWA-DPU. We describe the combined data products that we expect to return from the suite and provide to the Solar Orbiter Archive for use in scientific analyses by members of the wider solar and heliospheric communities. These unique data products will help reveal the nature of the solar wind as a function of both heliocentric distance and solar latitude. Indeed, SWA-HIS measurements of solar wind composition will be the first such measurements made in the inner heliosphere. The SWA data are crucial to efforts to link the in situ measurements of the solar wind made at the spacecraft with remote observations of candidate source regions. This is a novel aspect of the mission which will lead to significant advances in our understanding of the mechanisms accelerating and heating the solar wind, driving eruptions and other transient phenomena on the Sun, and controlling the injection, acceleration, and transport of the energetic particles in the heliosphere.

Stellar versus Galactic: the intensity of cosmic rays at the evolving Earth and young exoplanets around Sun-like stars

“…This finding is quite interesting because the velocity of the solar wind at close distances is currently unknown. NASA's Parker Solar Probe (Bale et al 2019) and ESA's Solar Orbiter (Owen et al 2020) have only recently begun to probe the solar wind at these distances. Thus, our simulation results are sensitive to parameters of the solar wind that are only now being observationally constrained.…”

Exploring the Properties of the Electron Strahl at 1 AU as an Indicator of the Quality of the Magnetic Connection Between the Earth and the Sun

“…Such information is important in determining the nature of the change in the magnetic connection into the corona that may be occurring when there is a change in the strahl intensity and a change in the magnetic-field orientation. Such an examination has been recently enabled by the heavy-ion measurements onboard Solar Orbiter with ≤30-s time resolution (Owen et al, 2020), measurements that are an order of magnitude faster than on previous solar-wind missions. 2) Examination of strahl changes on spacecraft closer to the Sun is important for a better determination of the interpretation of strahl-intensity changes.…”

Evaluating the Performance of a Plasma Analyzer for a Space Weather Monitor Mission Concept

“…We examine solar wind proton measurements, obtained by a typical top hat electrostatic sensor design. Our concept instrument is based on Solar Wind Analyser's Electron Analyser System (SWA‐EAS, Owen et al, 2020) on board Solar Orbiter, while similar electrostatic analyzer designs have provided successful measurements of plasma species in several space plasma environments (e.g., Barabash et al, 2006; Johnstone et al, 1997; McComas et al, 2017; Nilsson et al, 2007). In Figure 1, we show a schematic of our instrument and a single proton trajectory through its structure, in order to demonstrate the measurement principle.…”