Storage ring

Abstract: An overview of the KEKB accelerators is given as an introduction of the following articles in this issue, first by summarizing the basic features of the machines, and then describing the improvements of the performance since the start of the physics experiment.

Abstract: The measured response matrix giving the change in orbit at beam position monitors (BPMs) with changes in steering magnet excitation can be used to accurately calibrate the linear optics in an electron storage ring [1–8]. A computer code called LOCO (Linear Optics from Closed Orbits) was developed to analyze the NSLS X-Ray Ring measured response matrix to determine: the gradients in all 56 quadrupole magnets; the calibration of the steering magnets and BPMs; the roll of the quadrupoles, steering magnets, and BPMs about the electron beam direction; the longitudinal magnetic centers of the orbit steering magnets; the horizontal dispersion at the orbit steering magnets; and the transverse mis-alignment of the electron orbit in each of the sextupoles. Random orbit measurement error from the BPMs propagated to give only 0.04% rms error in the determination of individual quadrupole gradients and 0.4 mrad rms error in the determination of individual quadrupole rolls. Small variations of a few parts in a thousand in the quadrupole gradients within an individual family were resolved. The optics derived by LOCO gave accurate predictions of the horizontal dispersion, the beta functions, and the horizontal and vertical emittances, and it gave good qualitative agreement with the measured vertical dispersion. The improved understanding of the X-Ray Ring has enabled us to increase the synchrotron radiation brightness. The LOCO code can also be used to find the quadrupole family gradients that best correct for gradient errors in quadrupoles, in sextupoles, and from synchrotron radiation insertion devices. In this way the design periodicity of a storage ring's optics can be restored. An example of periodicity restoration will be presented for the NSLS VUV Ring. LOCO has also produced useful results when applied to the ALS storage ring [8].

Abstract: THE possibility of creating ordered ion beams in high-energy storage rings1,2 by means of electron and laser cooling has opened up a new era in accelerator physics The enhanced luminosity and suppressed momentum spread in such systems create the highest possible phase-space density The first experimental results were obtained by cooling 7Li+ beams to temperatures of a few kelvin or even to sub-kelvin temperatures3,4, and the ordered structures have been studied theoretically5–7 by methods of molecular dynamics Predicted configurations for the lowest ion densities have been observed in low-energy quadrupole storage rings8 and linear traps9 Recently we showed that at slightly higher ion densities helical structures are obtained10 Here we present a series of new experimental results on ordered ion structures in a quadrupole storage ring In order of increasing ion number, a linear chain of ions, a zig-zag structure, helical structures and finally multiple concentric shells could be observed The experimental results agree with molecular dynamics calculations

Abstract: A nearly monochromatic beam of 100% linearly polarized g rays has been produced via Compton backscattering inside a free electron laser optical cavity. The beam of 12.2 MeV g rays was obtained by backscattering 379.4 nm free-electron laser photons from 500 MeV electrons circulating in a storage ring. A detailed description of the g-ray beam and the outlook for future improvements are presented. [S0031-9007(97)03322-X]