A Rapid Cycling Flat-Topped Synchrotron Magnet System

The Princeton-Pennsylvania Accelerator (PPA), operating as a rapid cycling synchrotron at 19 Hz, produces an intense beam with a spill duty factor of 18% or less. The beam has the "RF structure" characteristic of PPA but also the energy modulation associated with the variation in magnetic field during an extended spill. Some years ago, a plan was formulated to provide a flat top to the magnet field waveform with a duty factor as high as 50%. This plan took advantage of the distributed nature of the magnet circuit which results in modest voltage stress on the individual components. Even so, implementation of the plan required the development of a 5kV rms, 1000A rms electronic switch. Also, static power supplies were required to replace the existing rotating machinery. Fairly sophisticated measures were required to regulate the magnet current during flat-top and to cope with the rather nasty transmission line modes of the circuit. The program has been essentially completed. Termination of the facility operating contract has prevented the actual use of the equipment for experimental purposes but all significant goals have been met and this paper describes the completed system and its performance.