Abstract
The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Solar Probe Plus is a four sensor instrument suite that provides complete measurements of the electrons and ionized helium and hydrogen that constitute the bulk of solar wind and coronal plasma. SWEAP consists of the Solar Probe Cup (SPC) and the Solar Probe Analyzers (SPAN). SPC is a Faraday Cup that looks directly at the Sun and measures ion and electron fluxes and flow angles as a function of energy. SPAN consists of an ion and electron electrostatic analyzer (ESA) on the ram side of SPP (SPAN-A) and an electron ESA on the anti-ram side (SPAN-B). The SPAN-A ion ESA has a time of flight section that enables it to sort particles by their mass/charge ratio, permitting differentiation of ion species. SPAN-A and -B are rotated relative to one another so their broad fields of view combine like the seams on a baseball to view the entire sky except for the region obscured by the heat shield and covered by SPC. Observations by SPC and SPAN produce the combined field of view and measurement capabilities required to fulfill the science objectives of SWEAP and Solar Probe Plus. SWEAP measurements, in concert with magnetic and electric fields, energetic particles, and white light contextual imaging will enable discovery and understanding of solar wind acceleration and formation, coronal and solar wind heating, and particle acceleration in the inner heliosphere of the solar system. SPC and SPAN are managed by the SWEAP Electronics Module (SWEM), which distributes power, formats onboard data products, and serves as a single electrical interface to the spacecraft. SWEAP data products include ion and electron velocity distribution functions with high energy and angular resolution. Full resolution data are stored within the SWEM, enabling high resolution observations of structures such as shocks, reconnection events, and other transient structures to be selected for download after the fact. This paper describes the implementation of the SWEAP Investigation, the driving requirements for the suite, expected performance of the instruments, and planned data products, as of mission preliminary design review.
Highlights
For centuries solar eclipses have provided brief glimpses of the solar corona, a highly structured and magnetized atmosphere that surrounds the Sun and extends throughout the solar system as the supersonic solar wind
The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation, described in this paper, is a four sensor instrument suite that provides complete measurements from several eV to tens of keV of the velocity distribution functions of electrons and ionized helium and hydrogen that constitute the bulk of the solar wind and coronal plasma, along with properties of other ions sorted by their mass/charge
Solar Probe Plus will allow us to answer fundamental questions about our closest star: Why is the corona millions of degrees hotter than the visible surface of the Sun? How does the corona produce the supersonic and variable solar wind? How are solar flares and coronal eruptions able to produce storms of energetic particle radiation? Successfully answering these questions would represent a major breakthrough in our understanding of the physics of energetic magnetized plasmas, allowing us to better understand and predict the evolution of the corona and solar wind and providing us with general insights into the physics of plasmas from the laboratory to exotic astrophysical environments
Summary
For centuries solar eclipses have provided brief glimpses of the solar corona, a highly structured and magnetized atmosphere that surrounds the Sun and extends throughout the solar system as the supersonic solar wind. The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation, described in this paper, is a four sensor instrument suite that provides complete measurements from several eV to tens of keV of the velocity distribution functions of electrons and ionized helium and hydrogen (alpha particles and protons) that constitute the bulk of the solar wind and coronal plasma, along with properties of other ions sorted by their mass/charge. SWEAP consists of the Solar Probe Cup (SPC), a Sun-viewing fast Faraday Cup designed to operate under extreme temperatures, and the Solar Probe Analyzers (SPAN), a combination of three electrostatic analyzers that make detailed measurements of ion and electron velocity distributions from the shadowed region behind the spacecraft heat shield.
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