The slow-ground-motion monitoring based on the hydrostatic leveling system in J-PARC linac

A slow-ground-motion monitoring system has been developed for J-PARC (Japan Proton Accelerator Research Complex) linac to improve its operational stability. The monitoring system utilizes a hydrostatic leveling system with non-contact water-level sensing, and it has remote water-level control capability. Online calibration has been performed with a remote water-level control and an accuracy of 0.02 mm over the range of 1 mm has been obtained. Characteristic time response of this monitoring system is evaluated based on a hydraulic model. This simple modeling can simulate dynamic fluctuation of a multi-vessel system with various conduit network topologies. We have performed a forced water-level variation test, and confirmed that the modeling shows a reasonable agreement with experiments. The time resolution of this system is confirmed to be around 540 s with a filling tank for remote water feeding. To demonstrate the system performance, the slow ground motion of J-PARC linac has been measured with this monitoring system. A periodic ground movement is observed with this system, which is supposed to be induced by a tide effect. The stability of the accelerator tunnel has some local variation possibly due to the difference of the geological circumstances and the inequality in the foundation constructions.