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Description
The final-focus superconducting magnet system (QCS) in the SuperKEKB interaction region is housed in a large cryostat whose position is continuously monitored by gap sensors. This monitoring system has recorded the cryostat response to numerous earthquakes with a wide range of magnitudes and epicentral distances, providing a unique opportunity to study the mechanical behavior of a large superconducting magnet system under seismic excitation.
In this paper, we analyze the cryostat motion during several representative earthquakes, from small local events to stronger regional earthquakes. Transient displacements, recovery characteristics, and residual position shifts are correlated with earthquake magnitude, epicentral distance, and ground motion measured at KEK. The results show that the cryostat responds predominantly elastically, returning close to its original position after most earthquakes, while stronger events can produce measurable residual displacements and influence the long-term positional drift. These observations provide valuable insight into the mechanical stability of the interaction region and contribute to the design, alignment, and long-term operation of superconducting magnet systems for future collider facilities.
