Solar Wind and Pickup Ion (SWAPI) Instrument on NASA’s Interstellar Mapping and Acceleration Probe (IMAP)

The Solar Wind and Pickup Ion (SWAPI) instrument onboard the Interstellar Mapping and Acceleration Probe (IMAP) is a top-hat electrostatic analyzer designed to measure energy-per-charge distributions of solar wind protons (H+), alpha particles (He2+), and interstellar pickup ions (PUIs; combined H+ and He+) across a range of 0.1 to 20 keV/q. These measurements are essential for advancing understanding of the solar wind dynamics, particle acceleration, and physical processes governing the heliosphere. SWAPI builds on the heritage of the Solar Wind Around Pluto (SWAP) instrument on New Horizons, with enhancements tailored for continuous operation at 1 au. A key innovation is its grounded aperture grid assembly, which passively attenuates solar wind flux by approximately three orders of magnitude while preserving a large geometric factor for PUIs. The instrument’s electro-optics include an electrostatic analyzer, a field-free flight path, and a coincidence detector system employing an ultrathin carbon foil and dual Channel Electron Multipliers (CEMs), enabling effective background suppression with some species discrimination. These capabilities support detailed studies of solar wind transients, pickup ion distributions, and the interaction between the solar wind and the interstellar medium. SWAPI also contributes to IMAP’s space weather system, extending ACE-like solar wind monitoring with enhanced time and energy resolution, and provides real-time data for heliospheric modeling and forecasting.