The FPI experiment comprises the Dual Electron Sensors (DES) and the Dual Ion Sensors (DIS). Each set of instruments is made of 4 dual sensor heads on each of the four satellites (thus 8 heads each). Each particle detection head measures in a 180° plane, oriented North-South in a plane containing the spin axis of the spacecraft, and divided into 16 anodes of 11.25° each. The entrance deflection system permits each head to steer the arrival direction of the particles (typically in 4 directions), and, since all 8 heads are placed equidistant around the spacecraft, permit to perform measurements of the full three-dimensional particle distribution functions in just 30 ms for electrons and 150 ms for ions.
The full FPI description is provided in Pollock et al. (Space Sci. Rev., 2016). The full 3D distributions, in particular at electron scales and at more than 100 times faster cadence than past missions, permit to study collisionless plasma process in an unprecedented fashion, and is crucial for the study of the main mission target: the electron diffusion region of magnetic reconnection.
IRAP, with the support of CNES, has contributed hardware to the mission through the provision and calibration of the set of micro-channel plate detectors (32 flight models) for the DIS ion instruments.
Development Institution: Goddard Space Flight Center (PI: B. Giles), ISAS / JAXA (Lead-CoI: Y. Saito), IRAP (CoI : V. Génot & J.-A. Sauvaud), LAB (CoI : B. Lavraud)