The Fast Plasma Investigation measures 3D ion and electron phase space distributions at 150 ms and 30 ms, respectively. This high temporal resolution in 3D phase space measurements is the first in the history of scientific space flight.
Each of the four MMS spacecraft has eight high-speed ion sensors and eight high-speed electron sensors (packaged in pairs as four dual ion spectrometers (DIS) and four dual electron spectrometers (DES)).
These dual spectrometer packages are evenly distributed around the spacecraft perimeter so that full azimuthal sampling of phase space does not depend on the spin of the spacecraft as had been common for previous missions. This allows sampling at speeds limited only by the stepper speeds of the spectrometer high voltage power supplies and the counting statistics possible within the measurement accumulation times.
An important consequence of this approach is that each 3D phase space distribution is "stitched together" from the measurements of those eight spectrometers, which under certain environmental conditions can present an inter-calibration challenge that should be evaluated and managed as part of the user's data analysis approach.
Fields of View (FPI Skymap)
Each group of four dual spectrometers includes twelve independent high voltage power supplies: eight for detector bias and four (each with three outputs) for energy and angle selection,
Authors for this section: Barbara Giles, Craig Pollock, Amy Rager