Phase loop bandwidth measurements on the Advanced Photon Source 352-MHz RF systems

Phase loop bandwidth tests were performed on the Advanced Photon Source storage ring 352-MHz RF systems. These measurements were made using the HP3563A Control Systems Analyzer, with the RF systems running at 30 kilowatts into each of the storage ring cavities, without stored beam. An electronic phase shifter was used to inject approximately 14 degrees of stimulated phase shift into the low-level RF system, which produced measurable response voltage in the feedback loops without upsetting normal RF system operation. With the PID (proportional-integral-differential) amplifier settings at the values used during accelerator operation, the measurement data revealed that the 3-dB response for the cavity sum and klystron power-phase loops is approximately 7 kHz and 45 kHz, respectively, with the cavities the primary bandwidth-limiting factor in the cavity-sum loop. Data were taken at various PID settings until the loops became unstable. Crosstalk between the two phase loops was measured