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Description
In the case of large accelerator facilities, as SPring-8, of which circumference is about 1.5 km, a long term and seasonal stability of a floor in the accelerator tunnel is one of the important factors. The SPring-8 storage ring is located on bedrock area. So, a re-alignment of the storage ring, corresponding floor deformation, has never been performed since starting operation in 1997.
SPring-8 upgrade plan is being designed. The ultra-low emittance storage ring requires about 50 micro-meters (1-sigma) as a tolerance between neighboring two girders. The tolerance is 4 times smaller than that for the present SPring-8. Then we have investigated vertical floor deformations in the tunnel, and identified the position and the cause of large local deformations.
In 1996, before the starting operation, a difference in height of one round of the ring was 1 mm. In 2015, the difference had increased to 4 mm. For analysis, changes of height difference between neighboring two control points were used instead of changes of height. The long-term deformation was mainly found over the underground RF rooms. The seasonal deformation was mainly found over the drain pipes and underground passages. The result of the observation and the analysis are summarized.