Experience with Control of Frequency, Amplitude, and Phase

In superconducting accelerators, requirements for frequency, amplitude, and phase control are different from those used for normal conducting activities. Superconducting cavities have a very narrow bandwidth and are therefore highly sensitive to mechanical perturbations. Significant phase and amplitude errors are induced by the resulting frequency variations. Perturbations can be excited by microphonics, changes in pressure, or Lorentz forces. Slow ( and lt;1 Hz), large changes in frequency are typically corrected by a frequency tuner, while faster changes ( and gt;1Hz) are corrected by modulation of the incident rf power in amplitude and phase. The basic principles of rf control systems used in superconducting electron accelerators and their operational performance have been presented by Graf[1]. The present paper extends this earlier work. Operational experience gained at various accelerator facilities and performance details of the CEBAF rf control system are presented