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Naoe, Takashi; Kogawa, Hiroyuki; Tanaka, Nobuatsu*; Futakawa, Masatoshi
Advanced Experimental Mechanics, 4, p.17 - 21, 2019/08
We have introduced the following two techniques to mitigate the pressure wave-induced cavitation damage in the mercury target. One is the gas microbubble injection into the flowing mercury, and the other is the double-walled structure with a narrow gap channel at the proton beam entrance portion of the mercury vessel. The latter is expected to mitigate the cavitation damage due to the high-speed liquid flow (
4 m/s) and the narrow gap boundary (2 mm). To quantitatively investigate the effect of double-walled structure on cavitation damage, cavitation damage tests were conducted by parametrically changing mercury flow velocity and gap width of the channel wall. The results showed that the damage evaluated as a surface roughness was reduced by increasing the flow velocity. By contrast, the effect of gap width on cavitation damage was hardly observed under flowing conditions.
Futakawa, Masatoshi
Proceedings of 13th International Symposium on Advanced Science and Technology in Experimental Mechanics (13th ISEM'18) (USB Flash Drive), 6 Pages, 2018/10
Issues on the engineering technologies relating to high-power spallation neutron sources with liquid metals are introduced. The present status on research activities and results was reviewed.
Kawamura, Shunsuke; Naoe, Takashi; Ikeda, Tsubasa; Tanaka, Nobuatsu*; Futakawa, Masatoshi
no journal, ,
A mercury enclosure vessel made of stainless steel is used as a spallation target in the pulsed spallation neutron source at J-PARC. It is severely damaged by the cavitation induced with pressure waves in association with the pulsed proton beam injection. A double-walled structure with a narrow mercury channel was adopted in the front end of the target vessel to reduce the cavitation damage. It has been experimentally demonstrated that the cavitation damage could be mitigated in the narrow channel but its mechanism has been unclarified yet. In this study, we investigated the cavitation from growing to collapsing through visualizing the spark-induced cavitation bubbles under flow field using a high-speed video camera. Furthermore, we measured the wall vibration due to the cavitation bubble collapse with changing flow velocity parametrically. It was found that the microjet collided perpendicular to the wall in the stagnant flow condition while it collided with an inclined angle from the perpendicular direction, suggesting that the collision pressure on the wall was reduced by flowing.
Ikeda, Tsubasa; Kogawa, Hiroyuki; Naoe, Takashi; Kawamura, Shunsuke; Tanaka, Nobuatsu*; Futakawa, Masatoshi
no journal, ,
In the mercury target of the pulsed spallation neutron source at J-PARC, pressure waves are generated by the high-intensity pulsed-proton beam bombardment, resulting in inducing cavitation. Because the cavitation causes severe erosion damages on the mercury enclosure vessel made of stainless steel, suppressing the pressure waves and the cavitation are crucial issues to realize stable target operations at rated proton beam power of 1 MW. Gas microbubbles injection into flowing mercury is one of the prospective techniques to suppress pressure waves. At the J-PARC, a swirl-flow bubble-generator has been developed to generate microbubbles and installed in the mercury target. In order to improve the performance of the pressure wave suppression by increasing the amount of microbubbles, effects of the vane angle and throttling ratio of the Venturi on the amount of microbubbles were parametrically investigated through water experiments. The experimental results showed that the amount of the microbubbles was increased with decreasing the throttling ratio of the Venturi.