Trigger and Calorimeter Data Acquisition of the High-Energy Particle Detector Onboard the CSES-02 Satellite

This article describes the innovative system performing the trigger and the readout of the photomultiplier tubes (PMTs) for the high-energy particle detector (HEPD) onboard the second satellite of the China Seismo Electromagnetic Satellite (CSES) mission. The second HEPD is designed to measure cosmic rays covering an energy spectrum ranging from a few megaelectronvolts to several hundreds of megaelectronvolts. This high-precision detector consists of different subsystems: a solid-state tracker, a segmented trigger, a calorimeter composed of a tower of plastic scintillators, and two layers of lutetium-yttrium oxyorthosilicate (LYSO) crystals, along with a containment detector. The data acquisition (DAQ) process for the trigger, calorimeter, and containment detector is carried out by a single electronic board, relying on two Weeroc CITIROC application-specific integrated circuits (ASICs), which are being utilized in space for the first time. This board also generates and manages trigger signals for the entire detector. It effectively captures signals with distinct timing characteristics from plastic scintillators and inorganic crystals. Given the wide range of particle fluxes encountered during CSES’s orbit, adaptability of the trigger generation system becomes crucial, and DAQ is optimized to ensure consistent energy spectra measurement with a substantial duty cycle. The trigger system of the second HEPD implements concurrent trigger patterns and the ability to select DAQ strategies based on orbital zones and the presence of impulsive events. Each trigger configuration is designed to meet scientific demands concerning the field of view and the characteristics of the particles reaching the detector, with prescaling settings fine-tuned accordingly. In addition to monitoring particle bursts, trigger configurations specific to gamma rays will be tracked in 5-ms intervals to measure photon fluxes in the energy range from 2 to 20 MeV and provide sensitivity for impulsive events, such as gamma-ray bursts (GRBs). This article provides a comprehensive account of the design criteria, the architectural choices specifically adapted for space applications, and the original trigger management strategy. Additionally, this article presents an in-depth analysis of the performance of the trigger system and comprehensive results from laboratory and beam tests conducted on the qualification and flight models of second HEPD.