The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on SolarProbe 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.

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Spectral characteristics of low‐frequency plasma turbulence in a cometary environment have been determined using cross‐spectral analyses of magnetic field and plasma measurements made on board the Giotto spacecraft upstream of comet P/Halley. Two upstream regions have been identified, where the mean solar wind magnetic field was approximately parallel and perpendicular to the solar wind flow velocity direction, respectively. The two regions also differ with respect to magnetic field lines having been disconnected (connected) to the cometary bow shock in the quasi‐parallel (quasi‐perpendicular) regions. In the quasi‐perpendicular region the mean magnetic field and solar wind flow direction as well as the Giotto velocity relative to the comet are approximately mutually perpendicular to each other. Thus there is no Doppler shift between the observations made in the spacecraft and plasma frame of reference for parallel propagating waves in the quasi‐perpendicular region. In both regions the turbulence spectrum can be described by a power law with a spectral index steeper than that of a Kolmogoroff‐Obukov spectrum. In the quasi‐parallel region the observed turbulence clearly exhibits an Alfvénic character with dynamic alignment between magnetic field and flow found throughout the frequency range (1‐100 mHz) analyzed. Wave propagation is sunward for all spectral components, at least in the quasi‐parallel region. The turbulence cascade observed is probably driven by right‐hand resonant pickup water group ion instabilities in the quasi‐parallel region, while in the quasi‐perpendicular region, left‐hand ion cyclotron ring or Alfvén/ion anisotropy instabilities might be a possible driving mechanism. The polarization of the pump wave in the quasi‐parallel region is almost linear, while at higher frequencies almost linear as well as right‐ and left‐handed polarization is found. In the quasi‐parallel, region evidence for water group ion cyclotron harmonics has been found with the first harmonic exhibiting a slow mode character and all harmonics almost propagating along the mean magnetic field. In the quasi‐perpendicular connected region, no clear evidence has been found for the existence of backstreaming protons, reflected off the cometary bow shock, and associated upstream wave activity.

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Using four-point measurements of the Cluster spacecraft, the energy distribution was determined for magnetic field fluctuations in the solar wind directly in the three-dimensional wave-vector domain in the range |k|