Damage measurement of mercury target vessel and replacement to new target

Haga, Katsuhiro  ; Wakui, Takashi  ; Naoe, Takashi   ; Kogawa, Hiroyuki  ; Kinoshita, Hidetaka   ; Teshigawara, Makoto   ; Kasugai, Yoshimi  ; Seki, Masakazu; Hanano, Kohei; Suzuki, Toru; Ito, Manabu; Futakawa, Masatoshi  

Pitting damage of the target vessel wall is the crucial issue for the development of the high power mercury target. The damage is affected by the target vessel structure and the proton beam condition. In order to improve the evaluation accuracy of the pitting depth, the data of the pitting damage in the J-PARC mercury target was indispensable. Because the first target vessel of J-PARC was damaged by the earthquake, the preparations for cutting out specimens were carried out in advance. The surface dose rate is more than 10micro Sv/h. Then, we developed the cutting machine using hole saw, and we succeeded in cutting out specimens of the outer diameter of 50 mm. A spot which seems the cavitation damage was found by visual observation. The target replacement was also successfully finished. The radioactive gas release was more than the expectation, and it roused the necessity of reconsider the off-gas treatment system.