A Versatile Readout and Trigger System for the High Energy Particle Detector Onboard the Satellite CSES-02

This paper describes the system performing the readout of the PMT and the trigger for the High Energy Particle Detector (HEPD) onboard the second satellite of the China Seismo Electromagnetic Satellite (CSES) mission.CSES is a collaboration project of the Chinese National Space Administration (CSNA) and the Italian Space Agency (ASI), which aims at studying the ionospheric phenomena associated with earthquakes. Among the goals of CSES there is also the deepening of the theoretical studies on the mechanism of preparation processes of seismic events. In order to perform a comprehensive study of ionospheric phenomena, the mission has been designed to build a constellation of multi-instrument satellites.One of the instruments on board, the High Energy Particle Detector (HEPD), is developed by the Italian part of the Collaboration. The HEPD is designed to detect cosmic rays, i.e. electrons and protons, as well as light nuclei, in the energy range between a few MeV and a few hundreds of MeV. The instrument is composed by a tracker, a trigger system and a calorimeter surrounded by a veto system.The trigger board, main focus of this paper, performs the readout of all the detectors based on scintillators (trigger, energy and veto), furthermore, it issues and manages all the trigger signals for the whole apparatus. Since along the orbit the HEPD encounters different fluxes, it is necessary to switch between different trigger configurations in order to match the amount of data the instrument is able to process and send on ground. Each trigger configuration corresponds to different field of view and subset of particles viewed from the apparatus.This paper will provide a thorough description of the design criteria and the architecture of the trigger and a summary of the trigger performance studies.