Q Measurement with Swept RC Filter for Automatic Data Acquisition and Display

This paper describes an automatic Q measurement system (Q = fbetatron/frevolution) which was developed and installed at the 28 GeV Proton Synchrotron of CERN. At the desired moment the beam is excited to 1mm betatron oscillations by means of a programmed full aperture air kicker. The frequency spectrum which appears at a beam position pick-up station contains the non integer part of the Q value as the lowest frequency. A voltage controlled RC filter scans the pick-up signal spectrum. When the lowest frequency of the spectrum is attained, a feedback loop switches the filter to a constant frequency. The ratio measurement (normalization to the revolution frequency) is performed by counting the doubled acceleration frequency during 10 periods of the filter output frequency. The counter output is fed to a computer which displays after data handling the Q value on an alphanumeric cathode ray tube. The measurement time for the acquisition of the horizontal or vertical Q value is less than lms. The resolution of the measurement is ΔQ = 0.001.