Conceptual Design Reports

CDR chapter 9 - Timing and Synchronization

The FERMI timing and synchronization (T&S) scheme is based on a hybrid system utilising both “pulsed” and continuous wave (CW) timing techniques. The “pulsed” technique has been originally developed at MIT [1]: an ultra-low phase noise pulsed laser, called optical master oscillator (OMO), is locked to the radiofrequency reference generator. Its pulses distributed over dispersion compensated fiber links (FO) give the time reference to all the “pulsed” timing clients, such as lasers and diagnostics devices The “CW” timing technique, developed by LBNL at Berkeley [2] is based on a frequency stabilized CW laser amplitude modulated by the radio frequency (RF) of CW timing clients, such as low level RF systems. In this scheme, the FO links are stabilized using the optical mixing concept which fully exploits a carrier frequency 105 times higher than the repetition rate of the pulsed system. The FERMI timing system is compatible with both the European (fS-band-EU=2.998010 GHz) and U.S. (fS-band-US = 2.856 GHz) S-band frequencies, a  ecessary condition since the fourth harmonic (X-band) linearizer, that is part of the FEL design, will work at the US frequency. The greatest common divisor of these two frequencies is the coincidence frequency fCOIN (15.779 MHz) used to generate the "bunch clock" at the FEL repetition rate frequency fbunch=10-50 Hz. At each period of the coincidence frequency waveform the rising slopes of the (EU) S-band and the (US) aX-band waveforms overlap, thus providing the required phase coincidence. ... Retrieve pdf