Distributed digital data acquisition system with network time synchronization

Large scale nuclear physics experiments often use arrays of radiation detectors, which can be physically separated – in different rooms, near and remote to a target, and/or at different positions in the beam. To detect related events, time synchronization of the detector readout electronics is essential. In most existing large digital data acquisition systems, time synchronization is accomplished by sharing clock, trigger, and reset signals within and between chassis. This works well over short distances, but requires dedicated cabling and/or modules and becomes cumbersome for widely separated arrays. Statement of how it is being addressed: Recently, techniques and standards have been developed to synchronize time in network devices, for example the “Precision Time Protocol” (IEEE 1588) and the higher performance “White Rabbit” project. These techniques can reach low/sub-nanosecond time synchronization between processors. In this project, these techniques will be used to develop a practical, compatible, low cost product for nuclear physics applications, i.e. bringing the precision network timing to the front end data acquisition where detector pulses are detected, captured and timestamped. Achievements in Phase I: An existing detector readout module, the Pixie-Net, was adapted in hardware and firmware to tag detector events with timestamps derived from the network time synchronization techniques. It achieved time resolutions in the range of 1300ns to 200ps, depending on signal source, network, and synchronization technique. A concept for software triggering was developed, based on timestamped data rather than hard wired trigger pulses. Plans for Phase II: The Pixie-Net will be upgraded to be fully compatible with the White Rabbit technique, for higher precision, more readout channels, and higher data bandwidth. The software triggering concept will be implemented as an open source data acquisition prototype, for researchers to use as is or to integrate in a larger software framework. For backwards compatibility, converters and adapters to existing shared clock techniques will be developed. Commercial applications and other benefits: The primary benefit of the project is to enable researchers to synchronize detector readout electronics in physically separated systems. This will simplify large nuclear physics experiments, by reducing cabling requirements and by making it easier to merge data streams from different systems (since tagged with universal date/time). Beyond nuclear physics research, the technique may be used in homeland security (e.g. synchronizing portal monitors) or astrophysics (e.g. synchronizing arrays of cosmic ray detectors). General purpose clock/trigger adapters may find a market in “ground based precision timing” applications such as cellular networks and financial transactions