Description: Modern data acquisition systems are becoming more heterogenous and distributed. This presents new challenges in synchronization of the different elements of this event-driven architecture. The building blocks of the data acquisition system are digitizers, either flash digitizers or integrating digitizers of time, pulse height or charge. These elements respond in real-time to convert electrical signals from detectors into digital form. The data from each detector element is labeled with a precisely synchronized time and transmitted to buffers. The total charge, the number of coincident elements or other information summaries are used to determine if something interesting has happened, that is, forming a trigger. If the trigger justifies it, the data from the elements are assembled together into a time-correlated event for later analysis, a process called Event Building. At present the elements tend to be connected by buses (VME, cPCI), custom interconnects or serial connections (USB). In certain types of experiments at FRIB, low event rates of 1 to 10 kevents-s are anticipated, with dense data streams from FADC-based detector systems. The large latencies possible in highly buffered flash ADC architectures can be used to advantage in the design of the architecture.
A concept of the next generation data acquisition system is that it will be ultimately composed of separate ADC's for each detector element, connected by commercial network or serial technology. Development is required to implement the elements of this distributed data acquisition over commercially available network technologies such as 10 Gb Ethernet or Advanced Telecommunications Computing Architecture (ATC). The initial work needed is to develop a software architecture for a system that works efficiently in the available network bandwidth and latencies. The elements desired in the architecture are to (1) synchronize time to a sufficient precision, as good as 10ns or better to support Flash Analog-to-Digital Converter (FADC) clock synchronization, 100ns or better to support trigger formation and event building, (2) determine a global trigger from information transmitted by the individual components (3) notify the elements of a successful trigger, in order to locally store the current information, (4) collect event data from the individual elements to be assembled into events and (5) software tools to validate the function of the synchronization, triggering and event building during normal operation. The synchronization of time is critical to the success of this architecture, as is the constant validation of the synchronization.
Grant applications are sought for any of 1) development of the software architecture that specifies a functional model for the individual elements of the system, the high level network protocols, and requirements on the communications fabric for given data rates and system latencies, including a portable software implementation of the elements of the architecture, 2) hardware modules to implement the detector digitizer on Ethernet, and 3) time distribution protocols and hardware to support this architecture.
Such an architecture and its implementation could form the basis of a standard for next generation data acquisition in nuclear physics, particularly at the FRIB