Novel phase-averaging reference system for the CiADS facility

The China initiative Accelerator Driven System (CiADS) requires a stable phase reference distribution system (PRDS) to provide low-drift reference signals for over 300 radio-frequency (RF) clients on its superconducting linac and beam transport lines. PRDS is realized using a coaxial cable that transmits 162.5 MHz reference signals, and the phase averaging technique will be employed to counteract phase drift caused by changes in the cable length due to temperature variations. This paper analyzes the limitations of the current technical approach and proposes an improvement based on a bi-line structure with unidirectional transmission of the reference signal and front-end phase locking. The design of the PRDS for the CiADS and signal processing in the low level radio-frequency (LLRF) system are detailed. The feasibility of the new scheme is verified by testing a prototype PRDS.