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Journal Articles

Evaluation growing and collapsing behaviors of cavitation bubbles under flowing condition

Kawamura, Shunsuke; Naoe, Takashi; Ikeda, Tsubasa*; Tanaka, Nobuatsu*; Futakawa, Masatoshi

Advanced Experimental Mechanics, 4, p.33 - 37, 2019/08

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.

Journal Articles

Implementation of a low-activation Au-In-Cd decoupler into the J-PARC 1 MW short pulsed spallation neutron source

Teshigawara, Makoto; Ikeda, Yujiro; Oi, Motoki; Harada, Masahide; Takada, Hiroshi; Kakishiro, Masanori*; Noguchi, Gaku*; Shimada, Tsubasa*; Seita, Kyoichi*; Murashima, Daisuke*; et al.

Nuclear Materials and Energy (Internet), 14, p.14 - 21, 2018/01

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

We developed an Au-In-Cd (AuIC) decoupler material to reduce induced radioactivity instead of Ag-In-Cd one, which has a cut off energy of 1eV. In order to implement it into an actual moderator-reflector assembly, a number of critical engineering issues need to be resolved with regard to large-sized bonding between AuIC and A5083 alloys by the hot isostatic pressing process. We investigated this process in terms of the surface conditions, sizes, and heat capacities of large AuIC alloys. We also show a successful implementation of an AuIC decoupler into a reflector assembly, resulting in a remarkable reduction of radioactivity by AuIC compared to AIC without sacrificing neutronic performance.

Oral presentation

Experimental evaluation of effect flowing condition on cavitation bubble growing and collapsing behaviors

Kawamura, Shunsuke; Naoe, Takashi; Ikeda, Tsubasa; Tanaka, Nobuatsu*; Futakawa, Masatoshi

no journal, , 

A target vessel enclosing mercury made of stainless steel is used for the J-PARC spallation neutron source. It is severely damaged by the pressure-wave-induced cavitation with injecting intense proton beam. The front end of the target vessel has a double-walled structure with a narrow channel was adopted to the vessel for expecting to reduce cavitation damage. Effect of cavitation damage mitigation in narrow channel has been experimentally demonstrated. However, damage mitigation mechanism is not clarified yet. As a first step of studies to understand the mechanism of cavitation damage mitigation in narrow channel, growth and collapse behaviors of the spark-induced cavitation bubbles under flow condition were observed by using a high-speed video camera. Furthermore, the wall vibration by cavitation bubble collapse was measured by parametrically changing the flow velocity. The experimental results showed that the ejection angle of the microjet ejected by bubble collapsing leaned towards flowing direction as the flow velocity increases. The wall vibration was reduced with increasing flow velocity.

Oral presentation

Experimental evaluation of characteristics of the microbubble generator using swirl flow

Ikeda, Tsubasa; Kogawa, Hiroyuki; Naoe, Takashi; Kawamura, Shunsuke; Tanaka, Nobuatsu*; Futakawa, Masatoshi

no journal, , 

In a mercury target used for the pulsed spallation neutron source at J-PARC, pressure waves are generated by the rapid thermal expansion of mercury due to the high-intensity pulsed-proton beam bombardment. They induces cavitation, causing severe erosion damage on the mercury enclosure vessel made of stainless steel. Gas microbubbles injection into mercury is one of effective techniques to suppress the pressure. At J-PARC, a swirl-flow bubble-generator has been developed and installed in the mercury target. Increasing the gas void fraction is effective to enhance the suppression effect. In this study, dependencies of the vane angle and reduction rate of the Venturi were parametrically investigated through a water experiment in order to optimize the swirl-flow bubble-generator for decreasing the aspiration pressure without increasing pressure drop. The result showed that the gas aspiration rate of the swirl-flow bubble-generator increased as the reduction rate at the Venturi increased.

Oral presentation

Visualization of cavitation growing and collapsing behaviors in narrow channel

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.

Oral presentation

Optimization of the swirl gas microbubble generator for a liquid mercury target vessel

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.

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