Speakers
Description
In this contribution, we describe the advantages of the pilot tone compensation technique that we implemented in a new BPM prototype. Injecting a fixed reference tone upstream of cables allows for a continuous calibration of the system, compensating the different behaviour of every channel due to thermal drifts, variations of cable properties, mismatches and tolerances of components.
Another key feature of this approach is that the pilot can be seen as a fixed beam: a parallel and independent demodulation of this signal returns a real-time diagnostic of the system status.
All of these features, combined with long term stability, reduced current dependence, and nanometer-scale accuracy are desirable for BPMs adopted in low emittance machines.
A BPM based on the pilot tone is currently operational in Elettra’s storage ring, connected to the global orbit feedback. It is capable of an equivalent RMS noise (@10 kHz data rate) for the pilot tone position of less than 200 nm on a 20 mm vacuum chamber radius, and a long-term stability better than 1 um in a 12-hour window.
Moreover, the possibility to improve further the compensation by means of tone frequency hopping is under investigation.
