Recent Status of the Pulsed Spallation Neutron Source at J-PARC

Proceedings of the 14th International Workshop on Spallation Materials Technology

et al. 2020

Self Cite

The target vessel, which enclosing liquid mercury, for the pulsed spallation neutron source at the J-PARC is severely damaged by cavitation caused by proton beam-induced pressure waves in mercury. To mitigate the cavitation damage, we adopted a double-walled structure with a narrow channel for the mercury at the beam window of the target vessel. In addition, gas microbubbles are injected into the mercury to suppress the pressure waves. The narrow channel disturbs the growth of cavitation bubbles due to the pressure gradient. After finishing service operation, the front end of the target vessel was cut out, allowing us to inspect the effect of these cavitation damage mitigation technologies on the interior surface. The damage depth of the cutout specimens was quantitatively investigated by the replica method. The results showed that the erosion depth due to cavitation in the narrow channel is clearly smaller than on the wall facing mercury with injecting gas microbubbles.

Section: Introductionsupporting

confidence: 63%

Mitigation of Cavitation Damage in J-PARC Mercury Target Vessel

Naoe

Kinoshita

Proceedings of the 14th International Workshop on Spallation Materials Technology

et al. 2020

Self Cite

“…After finishing the service operation, a 1 MW beam operation at 25 Hz was performed for one hour to confirm the integrity of the facility at the rated beam power of J-PARC. For the mercury target vessel, it was confirmed that the gas microbubbles injection was effective in reducing pressure waves at 1 MW [10].…”

Section: Targets No 2 and No 8 Operationmentioning

confidence: 88%

Effect of Gas Microbubble Injection and Narrow Channel Structure on Cavitation Damage in Mercury Target Vessel

Naoe

Kinoshita

et al. 2021

MSF

The target vessel, which enclosing liquid mercury, for the pulsed spallation neutron source at the J-PARC is severely damaged by cavitation caused by proton beam-induce pressure waves in mercury. To mitigate the cavitation damage, we adopted a double-walled structure with a narrow channel for the mercury at the beam window of the target vessel. The narrow channel disturbs the growth of cavitation bubbles due to the pressure gradient. In addition, gas microbubbles are injected into the mercury to suppress the pressure waves. After finishing service operation, the front end of the target vessel was cut out to inspect the effect of those cavitation damage mitigation technologies on the interior surface. The damage depth of the cutout specimens for the original design type and double-walled target vessels were quantitatively investigated by the replica method. The results showed that the double-walled target facing mercury with gas microbubbles operate 1812 MWh for an average power of 434 kW is equivalent to the damage of original design target operated 1048 MWh for average power of 181 kW. The erosion depth due to cavitation in the narrow channel is clearly smaller than on the wall facing bubbly mercury.

“…It took seventeen months since the redesigning the structure was started. In the about eight months of service operation, the beam power was ramped up to 500 kW [8]. After finishing the beam operation for the user program, this vessel achieved the operation under the maximum beam power of 1 MW for about 1 hour.…”

Section: Completion Of Beam Operation For Mercury Target Vessel #8mentioning

confidence: 99%

New Design and Fabrication Technology Applied in Mercury Target Vessel #8 of J-PARC

Wakui

Wakai

Proceedings of the 14th International Workshop on Spallation Materials Technology

et al. 2020

Self Cite

A mercury target vessel for the spallation neutron source at the J-PARC, which has the triple-walled structure, was improved to promote its robustness and reliability with conducting structural integrity simulations and mockup tests to confirm the suitable fabrication and inspection procedures. A monolithic structure fabricated by the wire electric discharge machining was adopted to reduce a number of welding lines. The total length of welding lines at the fore part of the mercury target vessel decreased drastically to approximately 53 %. After the weld, an immersion ultrasonic testing which could detect small defects of more than 0.2 mm was adopted as a nondestructive inspection method. Stable beam operation at the beam power of 500 kW has been achieved and experienced the maximum beam power of 1 MW for an hour during a beam experiment.