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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.

  • MMS3 DIS008 energy sweep limited to maximum of 21 keV.
  • MMS4 DES1 (DES210) HV801 optocoupler (ESA high range stepper circuit) failure has left the unit permanently disabled, as of 5Jun2018 12:43 UTC. ref
  • MMS4 DES0 (DES215) HV801 optocoupler failure (Deflector0 high range stepper circuit) allows the ESA to sweep the full range of energies at one extreme, uncalibrated deflection angle, as of 15Jul2018 00:49 UTC. This spectrometer has not been in operation since the optocoupler failure. ref

An important consequence of this approach is that each 3D phase space distribution is "stitched together" from the measurements of 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. See Data Analysis Checklist.

Fields of View: the 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

For publications, cite the following references:

for general use of the FPI data:

– Pollock, C., Moore, T., Jacques, A. et al. Fast Plasma Investigation for Magnetospheric Multiscale. Space Sci Rev (2016) 199: 331. https://doi.org/10.1007/s11214-016-0245-4.

for use of the FPI quarter moment data:

– Rager, A. C., Dorelli, J. C., Gershman, D. J., Uritsky, V., Avanov, L. A., Torbert, R. B.,…Saito, Y. (2018). Electron crescent distributions as a manifestation of diamagnetic drift in an electron-scale current sheet: Magnetospheric Multiscale observations using new 7.5 ms Fast Plasma Investigation moments. Geophysical Research Letters, 45, 578–584. https://doi.org/10.1002/2017GL076260

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