Development of circuits and system models for the synchronization of the ILC crab cavities

The ILC reference design report (RDR) recommends a 14 mrad crossing angle for the positron and electron beams at the IP. A matched pair of crab cavity systems are required in the beam delivery system to align both bunches at the IP. The use of a multi-cell, 3.9 GHz dipole mode superconducting cavity is proposed, derived from the Fermilab CKM cavity being developed as a beam slice diagnostic [1]. Dipole-mode cavities phased for crab rotation are shifted by 90deg with respect to similar cavities phased for deflection. Uncorrelated phase errors of 0.086deg (equivalent to 61 fs) for the two cavity systems, gives an average of 180 nm for the relative deflection of the bunch centers. For a horizontal bunch size sigma_x = 655 nm, a deflection of 180nm reduces the ILC luminosity by 2%. The crab cavity systems are to be placed ~30 m apart and synchronization to within 61 fs is required; this is on the limit of what is presently achievable. This paper describes LLRF circuits under development at the Cockcroft Institute for proof of principle experiments planned on the ERLP at Daresbury and on the ILCTA test beamline at FNAL. Simulation results for stabilisation performance are also given.