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X-Ray Storage Ring

Introduction & History

The X-ray ring at the National Synchrotron Light Source was one of the first storage rings designed as a dedicated source of synchrotron radiation. The final lattice design was completed in 1978 shortly after funding was approved. Construction started in FY 1979 and installation of the magnets was well underway by the end of FY 1981. The first stored beam was obtained in September 1982. By FY 1985 the experimental program was in a rapid state of development, and by the end of FY 1990 the Phase II beamlines and insertion devices were being brought into operation. Implementation of global orbit feedback systems stabilized the orbit for all users, and local orbit feedback provided enhanced stability for the insertion device beamlines. In Spring 1993, a current of 500 ma was stored at 2.5 GeV. Also the vertical emittance was reduced by a factor of six down to below 2 Angstroms, corresponding to a horizontal-vertical coupling of 0.002. In 1996 operating current was increased to 350 mA at 2.584 GeV. In period of 1999-2000 X-ray ring has had alternating operations between high emittance lattice at 2.800GeV and low emittance lattice at 2.584 GeV. In August 2000 the ring started regular operations with low emmitance lattice at 300 mA, 2.800GeV. The increase of energy together with the reduction of vertical emittance yields an order of magnitude increase in brightness.

The lattice design for the X-ray ring is an eight superperiod Green-Chasman or double bend achromatic lattice with a circumference of ~ 170 meters. The achromatic bend is comprised of two 22.5 degree dipole bending magnets and a single focusing quadrupole. The dispersion free insertion straight sections are bounded by quadrupole triplets. The beta functions at the insertion center are quite small, betax = 1.5 m and betay = 0.33 m, resulting in very small transverse beam dimensions, but somewhat larger angular spread. Some advantages of low beta insertions are: the effect of the wiggler magnetic fields on the lattice are minimized, the brightness is optimized for short high- field wigglers, and the low vertical beta function allows the development of very small gap devices situated at the insertion center. An important disadvantage of low beta insertions is that orbit variations can result in large vertical angular deviations which could illuminate uncooled portions of the vacuum chamber with high power wiggler radiation. For this reason it has been necessary to develop special active interlock systems which use pick-up electrodes on either end of the straight section to detect orbit motion and to dump the electron beam if orbit movements are too large.