The data acquisition and transport design for NEMO Phase 2

Many high energy physics experiments (Auger, IceCube, NEMO, Km3Net) currently taking data or planned in the near future consist of big and sparse detectors that acquire a huge amount of data. This kind of topology requires the ability to acquire physics information in different places of the detector and correlate them using the occurrence time, usually with a sub-ns precision. The architecture described here provides a real-time data transport layer, used to implement the data acquisition system for the NEMO experiment, and consists of a synchronous link with fixed and deterministic latency. The system clock, distributed at every level of the apparatus, has been derived by the signals provided by a GPS receiver during the operating configuration. The aim of this contribution is to give an overview of the NEMO electronic system: the underwater electronics sample signals from photomultipliers and acquires slow-control data from both oceanographic instruments and dedicated sensors, allowing to monitor the operational conditions of the apparatus. The whole data are sent to the laboratory through a fully bi-directional fiber optic link. On-shore the data are received by dedicated boards that distribute them to the first-level trigger and to the slow-control system. A description of the different stages of data acquisition and transport will be given.