TOF clock system for BES III

In this paper, a clock system providing high quality timing reference for Time-Of-Flight (TOF) electronics, as well as other sub-systems in the new Beijing Spectrometer (BES III) is presented, which includes RF clock transmission, low-jitter clock regeneration and distribution. In addition, a new clock synchronizing and monitoring mechanism is developed and implemented with off-the-shelf devices, which can force the TOF clock to precisely synchronize to the beam bunches in the accelerator. The experimental results show the clock jitter (RMS) is better than 11 ps (the design spec is 20 ps), and the synchronization function works quite robustly. Now the clock system has been assembled to the spectrometer and is operating steadily.