Real time global orbit feedback system for NSLS X-ray ring

The authors report on the design and commissioning of a real-time harmonic global orbit feedback system for the NSLS (National Synchrotron Light Source) X-ray ring. This system uses 8 pick-up electrode position monitors and 16 trim dipole magnets to eliminate 3 harmonic components of the orbit fluctuations. Because of the larger number of position monitors and trim magnets, the X-ray ring feedback system differs from VUV (vacuum ultraviolet) ring system in that the Fourier analysis and harmonic generation networks are comprised of MDAC (multiplying digital-to-analog converter) boards controlled by computer. The implementation of the global feedback system has resulted in a dramatic improvement in orbit stability, by more than a factor of five everywhere. Simultaneous operation of the global and several local bump feedback systems has been achieved.<>