On-Line Q Measurement during Phase Displacement Acceleration in the CERN ISR

A new technique for measuring Q-values in a coasting beam traversed by RF buckets has been developed based on the RF knock-out principle. At the same time as the bucket traverses the stack a sweeping oscillator excites the beam transversely inside the stack. The resonance created can be detected from a pick-up signal when its radial position coincides with the bucket position. The exciting oscillator is locked to this signal via a phase-locked loop and the Q-value can be measured and stored by a local data acquisition system. At the end of the RF sweep the data is transferred to a computer for further treatment. Automatic control of the working line during phase displacement acceleration is then possible.