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

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.