The trigger system for the HIRFL-CSR external-target experiment

A trigger system has been designed and implemented for the external-target experiment (CEE), which is under construction at the heavy ion facility in Lanzhou, cooling storage ring (HIRFL-CSR). The experiment aims at studying high-density nuclear matter properties with heavy ion collisions in the GeV energy regime. The trigger system adopts a master-slave structure and a serial data transmission mode using optical fiber to deal with multi subdetectors and long-distance signal flow. The trigger logic, based on the field programmable gate array (FPGA) technologies, can be accessed by means of command register and remotely reconfigured online according to the experimental settings. The trigger system has been tested in a test beam experiment involving the subdetector prototypes. It is demonstrated that the trigger system functions correctly and meets physical requirements of the experiment.