First in-flight performances of the High Energy Particle Detector on board CSES

The China Seismo-Electromagnetic Satellite (CSES) is a scientific mission devoted to the study of electromagnetic, plasma and particle perturbations of atmosphere, ionosphere, magnetosphere and Van Allen belts, with special focus on potential correlation between transient phenomena and high magnitude earthquakes. For this purpose, CSES comprises nine payloads, including the High-Energy Particle Detector (HEPD), developed by the Italian CSES-Limadou collaboration. HEPD is devoted to the observations of high energy Cosmic Rays in the range 3-200 MeV, measuring both the incident direction and the energy of the incoming particle, discriminating its nature (electrons, protons). The satellite, launched on February 2, 2018 from the Jiuquan Satellite Launch Center (Inner Mongolia, China), underwent the commissioning phase (February-July 2018) during which several configurations were set in order to define the optimal operational conditions throughout the foreseen 5-year mission duration. This paper describes the HEPD instrument, its energy calibration and first in-flight performances, with special emphasis on the calorimeter and trigger subsystems, demonstrating its sensitivity to different particle populations.