Cross-sectional view of the SWAPI sensor with blue trajectories that highlight the incident A stream of charged particles, mostly protons and electrons, that escapes into the Sun's outer atmosphere at high speeds and streams out into the solar system. and green that highlight PUIs. Yellow trajectories show the path of the secondary electrons generated from the foil to provide the coincidence timing.
The Solar Wind and Pickup Ion (SWAPI) instrument measures several different elements of the solar wind, including hydrogen (H) and helium (He) ions, and, on occasion, heavy ions produced by large events from the Sun. SWAPI also measures interstellar pickup ions (PUIs), whose material comes from beyond our solar system and moves along with the solar wind. Its data will provide information about the local ion conditions, such as temperature, density, and speed. This will also be used in the I-ALiRT data stream allowing space weather to be measured in real-time. The data from SWAPI will be valuable for understanding how the solar wind changes in response to the Sun’s behavior over time. SWAPI’s first-ever high time resolution measurements of helium PUIs will provide new insights into physical processes that accelerate charged particles and shape and change our global heliosphere.
At L1, where IMAP will observe, the solar wind is colder but much more intense than the hotter PUIs. The Solar wind particles flow mainly in one direction while PUIs enter SWAPI from all directions. SWAPI's entrance structure is designed to sort out these particles. First, the particles pass through "sunglasses” that decrease the solar wind by a factor of a thousand, and then through vanes that block deflected solar wind from overwhelming the weaker PUI signal.
SWAPI design and assembly is led by Princeton University.