Improvements of the APS storage ring klystron power supplies

Summary form only given. The Advanced Photon Source (APS) is a third generation synchrotron X-ray source that provides super-intense X-rays for basic and applied research in materials science, biology, medicine, chemistry, physics, geology and environmental science. The APS has been providing brilliant X-ray beams for users since April 1995. There are many complicated subsystems at the APS. One of the systems essential for operation of our accelerator is the high power radio frequency (RF) system. The RF systems consist of five, 1 MW, CW klystron stations, each having a 100 kV, 18 A power supply with a 1400 V SCR gated voltage regulation, a hard tube modulator, a 100 kV rectifier, and an ignitron crowbar unit. A major concern during initial commissioning and early operation of the APS was the reliability of its RF power systems. At the beginning of 1997, the APS machine was only delivering beams to users 75% of scheduled time. Approximately 70% of the lost beam time was caused by indiscriminate high voltage power supply interlock trips. Most of these trips were found to occur in the power supply crowbar cabinet and control electronics. The authors describe the nature and the steps taken to overcome these problematic trips.