The new ALICE data acquisition system (O2/FLP) for LHC Run 3

Abstract

ALICE (A Large Ion Collider Experiment) has undertaken a major upgrade during the LHC Long Shutdown 2. The increase in the detector data rates led to a hundredfold increase in the input raw data, up to 3.5 TB/s. To cope with it, a new common Online and Offline computing system, called O2, has been developed and put in production. The O2/FLP (First Level Processor) system, successor of the ALICE DAQ system, implements the critical functions of detector readout, data quality control and operational services running in the CR1 data centre at the experimental site. Data from the 15 ALICE subdetectors are read out via 8000 optical links by 500 custom PCIe cards hosted in 200 nodes. It addresses novel challenges such as the continuous readout of the TPC detector while keeping compatibility with legacy detector front-end electronics. This paper discusses the final architecture and design of the O2/FLP system and provides an overview of all its components, both hardware and software. It presents the selection process for the FLP nodes, the different commissioning steps and the main accomplishments so far. It will conclude with the challenges that lie ahead and how they will be addressed.