Real time closed orbit correction system

A global closed-orbit feedback experiment based upon a real-time harmonic analysis of both the orbit movement and the correction magnetic fields is described. The harmonic feedback system was constructed and tested on the 750 MeV vacuum ultraviolet ring of the NSLS (National Synchrotron Light Source) and implemented on a real-time basis using relatively simple electronics. The feedback forces the coefficients of a few harmonics near the betatron tune to vanish and significantly improves the global orbit stability. The result of the experiment in the ring using four detectors and four trims, in which maximum observed displacement was reduced by a factor of between three and four, is presented.<>