Distributed digital data acquisition system with network time synchronization

Large scale nuclear physics experiments often use arrays of radiation detectors. Arrays from the same experiment 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. Most existing large digital data acquisition systems for radiation detectors consist of a host computer linked to one or more chassis containing multi-channel detector readout electronics modules. Time synchronization in such systems is accomplished by sharing clock 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. Recently, timing techniques and standards have been developed to synchronize network devices (i.e. processors). The most relevant in this discussion is the Precision Time Protocol defined in the IEEE 1588 standard that has been shown to reach low/sub-nanosecond time synchronization between processors. In the proposed effort, this standard 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. An existing detector readout electronics module, the Pixie-Net, will be adapted in hardware and firmware to tag detector events with timestamps derived from the network time synchronization. While focusing on the current IEEE 1588 standard for immediate results, the implementation will allow for compatibility with other efforts improving or exceeding the standard, such as the “White Rabbit” project. Time resolution measurements will characterize performance and results will be compared to traditional clock sharing. A concept for software triggering will be developed, based on timestamped data rather than hard wired trigger pulses. Commercial applications and other benefits: The primary benefit of the proposed project is to provide researchers with a solution to synchronize detector data acquisition in physically separated systems. This is useful to reduce the complexity of large nuclear physics experiments, by reducing cabling requirements and in some instances allowing measurements that would not be feasible otherwise. The electronics developed in this project is designed to be practical, compatible, low cost, and can be used to upgrade existing readout electronics. 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).