抄録
A liquid mercury target system for the megawatt-class pulsed spallation neutron source in installed in the J-PARC. In the system, cavitation damage induced by pressure waves that are generated by proton beam injection at the beam window of the mercury target vessel is a key factor to decide lifetime of target because the damage degrade the structural integrity of the vessel. A double-walled structure with a narrow mercury channel was adopted to the vessel for expecting to reduce cavitation damage. In this study, the cavitation bubble behaviors of the growth and collapse under water flow field were investigated by using the combination of a spark discharge for bubble formation and a high-speed photography in order to determine the effective factor for mitigating cavitation damage in narrow channel. It showed the bubble collapse behaviors that the bubble was divided into two at the bubble central part under stagnant condition, while the bubble collapsed as a single in the case of flowing condition. Furthermore, we measured the equivalent diameter and wall vibration due to the cavitation bubble collapse with parametrically changing flow velocity. It was found that the maximum equivalent diameter of the cavitation bubble and the response vibrational acceleration of the wall are decreased with the increasing velocity. As the results, it was found that cavitation bubble collapse pressure was affected by flowing condition in the narrow channel.
