Inflight Calibration of the PEP JEI ion and electron spectrometer on the JUICE spacecraft

The plasma spectrometer JEI is an ion and electron spectrometer designed to observe the thermal and medium energy charged particle environement of Jupiter. It is part of the PEP instrument onboard JUICE. Meanwhile the instrument was switched on several times while JUICE was in the solar wind. The flyby through the Earth-Moon system in August 2024 was the first test of the instrument in a magnetospheric plasma and under higher radiation. We report on the instrument performance and on observations of charged particles in the solar wind, the lunar environment and during the crossing of the Earth magnetosphere.  Specifically the solar wind observations and the crossing of the Earth plasmasphere provided excellent opportunities to test the performance of the instrument and provide calibration parameters in prospect of the further cruise phase of JUICE and expected observations at Jupiter. The Earth plasmasphere crossings allowed some rare measurements of the plasmaspheric ion composition.