Assessment of Precise Time Protocol in a Prototype System for the ITER Neutral Beam Test Facility

Data acquisition and real-time control in nuclear fusion science are usually demanding with respect to the number of involved components, the amount of handled data, and the accuracy required in time reconstruction. The latter aspect becomes critical in new and future experiments that will be running for hours. In these conditions, the mechanisms used to generate and distribute time information, to keep synchronization in devices such as acquisition boards and processing nodes, and to label with a timestamp the acquired samples play an important role. The IEEE1588 Precise Time Protocol (PTP) is a standard for clock synchronization that can be implemented over an Ethernet network. The technology is being considered for the implementation of the timing system of the ITER Neutral Beam Test Facility to be built in Padova, Italy. A PTP network has been set up using commercial off-the-shelf PTP electronic components, PTP and non-PTP switches, with the purpose of assessing the synchronism in conditions similar to those expected in real application. The capabilities of the PTP standard and of PTP hardware have been assessed with different measurement methodologies. Data have been acquired and analyzed using internal capabilities of the PTP hardware, a histogram-enabled digital oscilloscope, and a couple of digital acquisition boards. In particular, the last measurement method is based on data acquisition hardware that is commonly used in fusion experiments. The different measurements of the synchronization performance are in good agreement. These measurements allow assessing the accuracy in time reconstruction and in particular its dependency on the network switches. Based on the results obtained, the tested PTP implementation can be considered a candidate for time reconstruction of signals with analog bandwidth up to 33 kHz.