An analog RF gap voltage regulation system for the Advanced Photon Source storage ring

An analog RF gap voltage regulation system has been designed and built at Argonne National Laboratory to maintain constant total storage ring RF gap voltage, independent of beam loading and cavity tuning effects. The design uses feedback control of the klystron mod-anode voltage to vary the amount of RF power fed to the storage ring cavities. The system consists of two independent feedback loops, each regulating the combined RF gap voltages of eight storage ring cavities by varying the output power of either one or two RF stations, depending on the mode of operation. It provides full operator control and permissive logic to permit feedback control of the RF system output power only if proper conditions are met. The feedback system uses envelope-detected cavity field probe outputs as the feedback signal. Two different methods of combining the individual field probe signals were used to generate a relative DC level representing one-half of the total storage ring RF voltage, an envelope-detected vector sum of the field probe RF signals, and the DC sum of individual field probe envelope detector outputs. The merits of both methods are discussed. The klystron high-voltage power supply (HVPS) units are fitted with an analog interface for external control of the mod-anode voltage level, using a four-quadrant analog multiplier to modulate the HVPS mod-anode voltage regulator set-point in response to feedback system commands