ESS, Lund, Sweden
The European Spallation Source (ESS) will be a cutting-edge research facility that uses neutrons to study the properties of materials. This paper presents the timestamping strategy employed in the neutron instruments of the ESS, to enable efficient data correlation across subsystems and between different sources of experiment data. ESS uses absolute timestamps for all data and a global source clock to synchronize and timestamp data at the lowest appropriate level from each subsystem. This way we control the impact of jitter, delays and latencies when transferring experiment data to the data storage. ESS utilizes three time synchronisation technologies. The Network Time Protocol (NTP) providing an expected accuracy of approximately 10 milliseconds, the Precision Time Protocol (PTP) delivering roughly 10 microsecond accuracy, and hardware timing using Microreseach Finland (MRF) Event Receivers (EVR) which can reach 10 nanoseconds of accuracy. Both NTP and PTP rely on network communication using common internet protocols, while the EVRs use physical input and output signals combined with timestamp latching in hardware. The selection of the timestamping technology for each device and subsystem is based on their timestamp accuracy requirements, available interfaces, and cost requirements. This paper describes the choice of method used for different device types, like neutron choppers, detectors or sample environment equipment and covers some details of the implementation and characterisation.
