Processing High-Bandwidth Bunch-by-Bunch Observation Data from the RF and Transverse Damper Systems of the LHC

The radiofrequency and transverse damper feedback systems of the Large Hadron Collider digitize beam phase and position measurements at the bunch repetition rate of 40 MHz. Embedded memory buffers allow a few milliseconds of full rate bunch-by-bunch data to be retrieved over the VME bus for diagnostic purposes, but experience during LHC Run I has shown that for beam studies much longer data records are desirable. A new "observation box" diagnostic system is being developed which parasitically captures data streamed directly out of the feedback hardware into a Linux server through an optical fiber link, and permits processing and buffering of full rate data for around one minute. The system will be connected to an LHC-wide trigger network for detection of beam instabilities, which allows efficient capture of signals from the onset of beam instability events. The data will be made available for analysis by client applications through interfaces which are exposed as standard equipment devices within CERN's controls framework. It is also foreseen to perform online Fourier analysis of transverse position data inside the observation box using GPUs with the aim of extracting betatron tune signals.