R&D on mercury target for spallation neutron source to improve the durability under high power operation, 1; Mechanism of damage mitigation effects by gas bubbles and damage observation results

Kogawa, Hiroyuki  ; Kawashima, Hiroyuki; Ariyoshi, Gen  ; Wakui, Takashi  ; Saruta, Koichi   ; Naoe, Takashi   ; Haga, Katsuhiro  ; Futakawa, Masatoshi  ; Soyama, Hitoshi*; Kuji, Chieko*; Ito, Kei*; Tanaka, Nobuatsu*

In a mercury target system of the J-PARC, an operation injecting microbubbles of helium gas into mercury is carried out to reduce the pressure waves that cause cavitation damage. It was confirmed the damage was mitigated by increasing the injection amount of gas bubbles, while the damage considered to be caused by impact pressure from the gas bubbles was observed. To improve durability, it is necessary to find the optimum bubble condition, and those are also important to evaluate the radiation damage of the vessel material and to develop a diagnosis technology. In this report, as the first report of the series, the outline of the development to improve the durability will be reported with the damage observation results.