A typical usage for RFoWR is to control and distribute RF signals generated by RF cavities in particle accelerators; for example, those at CERN and ESRF. Distributing the RF signal throughout the accelerator complex enables applications to monitor beam position, beam loss and other beam synchronous events.
An RFoWR system combines two technologies: Direct Digital Synthesis (DDS) and White Rabbit Ethernet. A good reference and introduction to DDS systems is provided by Analog Devices. DDS systems typically include:
- Numerically Controlled Oscillator (NCO).
- Phase to amplitude converter, often this is a look-up table but implementations vary.
- Digital to Analog Converter (DAC) to drive the output RF signal.
White Rabbit Ethernet networks achieve sub-nanosecond accuracy and fully deterministic timing by utilizing:
- IEEE 1588 (1588) Precision Time Protocol (PTP)
- Synchronous Ethernet (SyncE)
- Phase difference measurement and correction between master and slave nodes.
By transmitting phase and frequency setpoints at precise timestamps, every RFoWR receiver can be disciplined to operate their DDS system in the same way, and at the same time. Subsequently, all receivers reproduce an RF signal that is coordinated anywhere in the network, subject to some (deterministic) latency.
Within the RFoWR system, there are two types of devices:
- A master node - responsible for digitising the RF signal, packetisation and distribution.
- A slave node - receives the digitised RF signal, unpacks the contents and replays the RF signal.
Direct digital synthesis (DDS)
TBD
Information about existing RF over WR systems/projects
- European Organization for Nuclear Research (CERN, Switzerland/France)
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European Synchrotron Radiation Facility (ESRF, France)
- "Refurbishment of the ESRF accelerator synchronisation system using White Rabbit", G. Goujon et al., in ICALEPCS, 2017 (paper)
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Super Photon Ring – 8 GeV (SPring-8, Japan)
- "Timing Signal Distribution for Synchrotron Radiation Experiments usng RF over White Rabbit", T.Masuda, in ICALEPCS, 2019 (paper)