Smoothing of NSLS-II Storage Ring by Girder Survey

A smooth storage ring orbit, generally referring tothe tolerance of ± 100 micron for adjacent girders, is the goal of alignment when NSLS-II is running. With an existing initial good alignmentand a stabilizing trend of slab deformation, it’s unlikely to adjust girders in very large amount as there will besignificant impact to beam lines. Based on thispremise, the strategy of smoothing in NSLS-II isthat the girders are surveyed gradually instead ofa complete surveyof all the girders in storage ringin one short period of time.That is, the girders, along with its surrounding monuments, are measured in a non-continuous manner. Themeasurement interval of adjacent girders can be several weeks depending on maintenance schedule. The relative location of girders is of interested and all the girders can be measured eventuallywithin several years. This effectively solves the problems of limited manpower and instrument resource due to the very busy constructionactivitiesof new beam lines and very restrictedaccess time with tight user schedule.By best fitting the as-built location of adjacent girders with the normal, a smooth orbit can be maintained. The upstream and downstream girder centers can be hold tight so that there is minimum impact to its affiliatingbeam line.Corresponding to the tight tolerance of ± 30 micron of magnets on a common girder, the girder profile are monitored as part of the girder survey. On the contrary to the traditional assumption of that girder will hold the magnets tight, it has been found that the girders themselves are deforming along with time. The smoothing technique of NSLS-II has the ability to correct girder deformation and therefore the meaning of smoothing is extended to a broad sense of maintaining the girder profile within around ± 10 micron accuracy.