New design and fabrication technology applied in mercury target vessel #8 of J-PARC

Wakui, Takashi  ; Wakai, Eiichi  ; Kogawa, Hiroyuki  ; Naoe, Takashi   ; Hanano, Kohei; Haga, Katsuhiro  ; Takada, Hiroshi   ; Shimada, Tsubasa*; Kanomata, Kenichi*

A mercury target vessel of J-PRAC is designed with a triple-walled structure consisting of the mercury vessel and a double-walled water shroud with internal and external vessels. During the beam operation at 500 kW in 2015, small water leakages from a water shroud of the mercury target vessel occurred twice. Design, fabrication and inspection processes were improved based on the lessons learned from the target failures. The total length of welding lines at the front of the mercury target vessel decreases drastically to approximately 55% by adopting monolithic structure cut out from a block of stainless steel by the wire-electrical discharge machining. Thorough testing of welds by radiographic testing and ultrasonic testing was conducted. The fabrication of the mercury target vessel #8 was finished on September 2017 and the beam operation using it started. Stable beam operation at 500 kW has been achieved and it could experience the maximum beam power of 1 MW during a beam test.