Universal picosecond timing system for the Facility for Antiproton and Ion Research

The present article presents a system making it possible to produce time information at spatially separate points with picosecond range precision. By using this time information, the accelerator and storage rings of the Facility for Antiproton and Ion Research (FAIR) are to be synchronized. To do this, the rf cavities of these ring accelerators have to be controlled by signals having different phases and frequencies (0.4 to 5.4 MHz). Some frequencies of the signals are variable during acceleration due to what is referred to as ramp control. To enable synchronization of all these different signals, also during acceleration, the signals for controlling the cavities are not sent directly by the timing system, but instead two clock signals of constant frequency are sent. These clock signals are produced phase synchronously at different points up to 1 km apart and represent the time information. With the help of these clock signals, it is then possible to synchronize frequency generators that produce the signals actually needed for the cavities. Because of the universal character of the time information produced, it can be used not only to control the cavities but also to synchronize other processes. To transmit the clock signals, an optical network with dense wavelength division multiplex methods is used. The delay of the clock signals is measured and with the help of the delay information a reference generator produces, at the end of each transmission line, a phase-synchronous and phase-stable time reference. Since the delays of the clock signals are not constant due to environmental influences, they must be determined regularly. Using a prototype of this system, a precision of the time information of 21.2 ps on average was achieved. The short-term jitter exhibits a standard deviation of 7.57 ps. In addition to the description of the system, detailed information on noise characteristics is provided that can also be used to optimize other optical systems for transmission of time information.