Synchronisation of the LHC Betatron Coupling and Phase Advance Measurement System

The new LHC Diode ORbit and OScillation (DOROS) system will provide beam position readings with submicrometre resolution and at the same time will be able to perform measurements of local betatron coupling and beam phase advance with micrometre beam excitation. The oscillation sub-system employs gain-controlled RF amplifiers, shared with the orbit system, and followed by dedicated diode detectors to demodulate the beam oscillation signals into the kHz frequency range, subsequently digitized by multi-channel 24-bit ADCs. The digital signals are processed in each front-end with an FPGA and the results of reduced throughput are sent using an Ethernet protocol to a common concentrator, together with the orbit data. The phase advance calculation between multiple Beam Position Monitors (BPMs) requires that all DOROS front-ends have a common phase reference. This paper presents methods used to generate such a reference and to maintain a stable synchronous sampling on all system front-ends. The performance of the DOROS prototype synchronisation is presented based upon laboratory measurements.