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Phase Lock of Rapid Cycling Synchrotron and Neutron Choppers

The 500 MeV synchrotron of Argonne's Intense Pulsed Neutron Source operates at 30 Hz. Its beam spill must be locked to neutron choppers with a precision of ± 0.5 ¿s. A chopper and an accelerator have large and different inertias. This makes synchronization by phase lock to the 60 Hz power line extremely difficult. We solved the phasing problem by running both the Ring Magnet Power Supply (RMPS) of the synchrotron and the chopper motors from a common oscillator that is stable to 1 ppm and by controlling five quantities of the RMPS. The quantities controlled by feedback loops are dc current, injection current, ejection current, resonant frequency, and the phase shift between the synchrotron peak field and the chopper window.