A high sensitivity tune measurement system for BEPCII

Background The tune is one of the most important parameters of the storage ring which play a crucial role in the brightness optimization. The synchrotron radiation will suppress the oscillation and make the detection unusual difficulty without any kicker excitation.
Purpose A new high sensitivity tune measurement system is developed to show the real-time tune during the colliding.
Method Peak diode detectors are used to convert short beam pulses from a button BPM into slowly varying signals. Their DC components, constituting a large background related to beam offsets, are suppressed by series capacitors, while the small signals related to beam oscillations are passed to the subsequent stages for amplification and filtering.
Conclusion A direct diode detection technique based on the diode peak hold circuit could increase the sensitivity by hundreds time which gets a clearly tune peak even with synchrotron radiation and bunch-by-bunch feedback damping.