The upgraded HADES trigger and data acquisition system

Abstract

The HADES experiment is a High Acceptance Di-Electron Spectrometerlocated at GSI in Darmstadt, Germany. Recently, its trigger and data acquisitionsystem was upgraded. The main goal was to substantially increase the event ratecapability by a factor of up to 20 to reach 100 kHz in light and 20 kHz in heavyion reaction systems. The total data rate written to storage is about 400MByte/s in peak.In this context, the complete read-out system was exchanged to FPGA-basedplatforms using optical communication. For data transport a general-purposereal-time network protocol was developed to meet the strong requirements of thesystem. In particular, trigger information has to reach all front-end moduleswith latencies of less than 5 μs through up to 10 intermediate hubs in astar-like network setup. Monitoring and slow control features as well as readoutand trigger distribution were joined in a single network protocol made up bythree virtual channels with inherent arbitration by priority and a typical switchingtime of 100 ns. The full DAQ system includes about 550 FPGAs distributed over thecomplete detector system. For control and monitoring a virtual address spacespanning the whole network is provided. Data are merged by the network hubs intodata streams and passed on to a server farm using an Ethernetinfrastructure. Due to the electromagnetic noise environment, severaltransmission error detection and correction features were included.In collaboration with groups from experiments of the FAIR accelerator complex, further developments based on the versatile hardware and communicationprotocol are being pursued.