Assessment of IEEE 1588-based Timing System of the ITER Neutral Beam Test Facility

MITICA is one of the two ongoing experiments at the ITER Neutral Beam Test Facility (NBTF) located in Padova (Italy). MITICA aims to develop the full-size neutral beam injector of ITER and, as such, its Control and Data Acquisition System will adhere to ITER CODAC directives. In particular, its timing system will be based on the IEEE1588 PTPv2 protocol and it will use the ITER Time Communication Network (TCN) on a dedicated Ethernet LAN. Following the ITER device catalog, the National Instruments PXI-6683H PTP timing modules will be used to generate triggers and clocks synchronized with a PTP grandmaster clock. The “Lazy Trigger" technique, then, will be adopted to implement event-driven data acquisition without the need of any hardware link in addition to the Ethernet connections used to transfer data and timing synchronization. To evaluate the accuracy over time that can be achieved with different network topologies and configurations, a test system has been set-up consisting of a grand master clock, two PXI-6683H devices and two PTP aware network switches. In addition, a detailed simulation of the network and the involved devices has been performed using the OMNET++ discrete event simulator. The simulation parameters include not only the network and switches configuration, but also the PID parameters used in the clock servo controllers. A comparison between simulated and measured statistics is reported, together with a discussion on the possible optimal configuration strategies.