Clock Distribution and Synchronization Based on DDS for SHINE

Shanghai High repetition rate X-ray Free Electron Lasers and Extreme light facility (SHINE) is expected to be the first hard X-ray FEL facility in China, which has been under construction. Hundreds of devices will be integrated in such kind of accelerators typically, and the perimeter of the SHINE accelerator is about 3.1 km. In order to make sure all the devices work exactly in a uniform manner, a high-precision multi-node clock distribution and synchronization system is required. For the reference clock fed into the clock distribution system is about 9.028 MHz, standard White Rabbit (WR) protocol cannot directly deal with it. A promising solution is that extracting the frequency and phase messages of the input clock by the DDS circuit on the master node, and then recovering the clock in all slave nodes according to the received frequency and phase messages. While the working clocks of both master and slave nodes are synchronized using WR. A prototype electronics is designed, and efforts are devoted to both hardware and Field Programmable Gate Array (FPGA) logic design to achieve high precision clock synchronization, fine phase adjustment, and frequency tuning. Test results show that the prototype can achieve multi-node machine clock distribution and synchronization at several kilometers distance, and the synchronization accuracy is better than 0.7 ns with the skew jitter better than 18 ps RMS within a frequency range from about 1 Hz to 1 MHz. Moreover, the temperature drift is less than 2 ps/°C.