High accuracy alignment of magnets is one of the key issues for next-generation light sources. For the SPring-8 major upgrade, SPring-8-II, and the new 3 GeV light source in north-east Japan, multipole magnets need to be aligned on a straight section with an error of 25 micro-meters in a standard deviation, or within ±50 micro-meters peak-to-peak. With that goal in mind, we have developed a vibrating-wire alignment technique and experimentally investigated its performances. The technique observes the vibration amplitude and phase of a thin wire in the bore of a magnet applied with AC current so that we can directly align the magnetic center on straight without any fiducialization. However, it is necessary to verify the practical performance of the new technique prior to incoming new projects. For example, an imperfection of the wire linearity, including a wire sag and local kinks, may significantly deteriorate the accuracy of the alignment. In this report, we address the main error factors on the precise alignment using the vibrating-wire technique and present our experimental test results to discuss the feasibility of the new technique for future light sources.
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