Earthquake Measurements and Those Analysis on IR Components and Belle II Detector in KEK

Abstract

Earthquakes frequently occur in Japan. Even though countermeasures are thoroughly considered and well executed, earthquakes still impact facilities and experimental devices. The large relative displacements induced by an earthquake can damage beam pipe bellows and interfere with sub-detectors by causing the tolerance between them to disappear. Even magnet quenches have been triggered by induced voltages caused by the relative displacements between the superconducting solenoids (i.e., the detector solenoid and the compensating solenoids surrounding the final focus quadrupole magnets, or QCSs). In response, we installed acceleration sensors on the Belle II detector and mounted gap sensors on the QCSs to measure the relative displacements. These measurements enabled the characteristics of the earthquakes that have affected the Belle II detector to be analysed. Response spectrum analyses (RSAs) of the Belle II detector were conducted to evaluate the impact of earthquakes according to the ground motion measurements. We then compared the measurements to the RSA results, which led to an idea for a countermeasure.