CSES-01 (China Seismo-Electromagnetic Satellite) is a space mission dedicated to the study of the ionospheric environment, searching for disturbances that can be correlated to seismic activity. For this reason, the satellite is equipped with several instruments to monitor various physical parameters including the Earth's electric and magnetic field, ionospheric plasma principal parameters (i.e. density, temperature, and ions composition) and high energy particle flux fluctuations.
The High Energy Particle Detector (HEPD), built by the Italian CSES-Limadou collaboration, is designed to detect mostly electrons in the energy range between 3 MeV and 100 MeV and protons in the energy range between 30 MeV and 300 MeV. The detector is composed of a tracking system, a segmented layer of plastic scintillator (used for the trigger), a range calorimeter and a veto system.

After CSES-01 launch (February 2, 2018), the apparatus underwent the commissioning phase where its configuration was adjusted in order to guarantee optimal operational conditions in the space environment. Now the satellite is in stable data-taking mode.

In this work a description of the HEPD detector will be reported, focusing on the results of the electron and proton test beam calibrations. In addition, a particular relevance will be given to the presentation of the HEPD in-flight performance, such as its good capability in particle identification. The high statistic collected by HEPD, thanks to its large acceptance window, makes it perfectly suitable for the investigation of fluctuations in the charged particle fluxes.