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. (C) 2009 Elsevier B.V. All rights reserved.