A tune measurement system for the Tevatron using a phase‐locked loop

A system for continous real time measurement of betatron tune has been developed and installed for the Fermilab Tevatron and Accumulator ring. A phase‐locked loop, using a considerable amount of input signal preconditioning, is used to lock to a betatron oscillation harmonic in the Schottky detector output signal. This system has demonstrated the capability of measuring the Tevatron fractional tune to an accuracy of ±.002 at 100 Hz bandwidth. The desired tune spectrum line has a very low signal to noise ratio, undesired revolution frequency harmonics, frequency modulation with wide deviations, and amplitude modulation with levels to 100%. Shown are the techniques used to overcome some of these limitations, with examples of the systems accuracy and tracking performance.