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3rd International Workshop on Beam Orbit Stabilization - IWBS2004

Announcement First / Second Accommodation Registration Participants Program Overview Details Orals by Session Orals with Abstracts Download PDF (gs) Download for PDAs Presentation   Upload / Download Summary Support Information No. #1 / #2 / #3 Pictures Gallery #1 / #2 / #3 Upload / Download SLS & Sponsors WWW psi.ch Updated: 25.01.2005		NOISE SOURCE SUPPRESSION 1 Well before feedback systems, the identification and minimization or possible removal of noise sources were essential to the achievement of state-of-the-art orbit stability. The session covered different issues that nethertheless form a representative sample of cases. The residual orbit distortion associated with the operation of the IDs is one of the major instability sources for all of the synchrotron facilities. FF systems based on correction coils are generally implemented and can provide good performance for IDs with slowly varying gap/phase. In the case of devices with a relatively fast switching of the radiation polarization, specific noise suppression strategies are needed to take into account dynamic effects. In particular, the orbit distortion due to the operation of these devices must be clearly measured and disentangled from the background noise present in the beam, so that appropriate values of the correction coils look-up tables can be obtained. A case was presented for an APPLE II type undulator installed at SPring-8, with the radiation helicity varying at 0.1 Hz following a trapezoidal driving pattern. A novel method was shown that separates the effect of static and dynamic field errors. Given the linear behavior of the system, correction values that correspond to different driving patterns are obtained only by scaling the correction data associated to the dynamic field errors. With the general trend of synchrotron light sources towards ``top-up'' operation, perturbations produced on the stored beam by the injection shots are to be considered as an additional source of noise. In addition to the gating signals provided to the experimentalists to temporarily disable data acquisition, efforts are going on to make user transparent injections. A significant example was reported by SPring-8, where a combination of passive and active noise suppression techniques is adopted. The first include careful equalization of the kicker pulses, kicker re-alignment to avoid crosstalk in the vertical plane and adjustment of the strength ratio of the sextupoles inside the injection bump to minimize non-linear effects. The latter consists of FF systems on both planes based on pulsed corrector magnets. The transverse multi-bunch feedback also helps by shortening the duration of the perturbation. With such countermeasures in operation, SPring-8 users do not suspend data acquisition during injection. The cooling water flow can induce mechanical vibrations of the storage equipment (magnets, vacuum chamber etc.), which affect the beam stability through different mechanisms. At SPring-8 the magnetic field created by eddy-currents in a vacuum chamber vibrating inside quadrupoles produces orbit perturbations up to 200 Hz. The installation of additional supports has already improved the situation. Further progress is being made, however, by measurements and modal analysis of the chamber sections vibrations, which can be damped by specifically designed supports. The session closed with a report on the experience gained with the dynamic alignment system of the SLS, where magnets are rigidly mounted on girders which are equipped with a complete set of girder/BPM position sensors and girder movers. Girder re-alignment using the movers proved to be convenient. The different position sensors provide data that can be usefully correlated to temperature changes and long-term settlements. The potential for orbit correction by means of ``on-line'' girder adjustments has also been demonstrated, but the interactive use of the system still looks cumbersome due to its complexity, the intrinsic long response times and the non-negligible risk of the involved operations.