Architecture and implementation of the front-end electronics of the time projection chambers in the T2K experiment

The tracker of the near detector in the T2K neutrino oscillation experiment comprises three time projection chambers based on micro-pattern gaseous detectors. A new readout system is being developed to amplify condition and acquire in real time the data produced by the 124,000 detector channels. The cornerstone of the system is a 72-channel application specific integrated circuit which is based on a switched capacitor array. Using analog memories combined to digitization deferred in time enables reducing the initial burstiness of traffic from 50 Tbps to 400 Gbps in a practical manner and with a very low power budget. Modern field programmable gate arrays coupled to commercial digital memories are the next elements in the chain. Multi-gigabit optical links provide 140 Gbps of aggregate bandwidth to carry data outside of the magnet surrounding the detector to concentrator cards that pack data and provide the interface to commercial PCs via a standard Gigabit Ethernet network. We describe the requirements and constraints for this application and justify our technical choices. We detail the design and the performance of several key elements and show the deployment of the front-end electronics on the first time projection chamber where the final tests before installation onsite are being conducted.