Effect of gas microbubble injection and narrow channel structure on cavitation damage in mercury target vessel

Naoe, Takashi   ; Kinoshita, Hidetaka   ; Kogawa, Hiroyuki  ; Wakui, Takashi  ; Wakai, Eiichi  ; Haga, Katsuhiro  ; Takada, Hiroshi   

The mercury target vessel for the at the J-PARC neutron source is severely damaged by the 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 vessel. In addition, gas microbubbles were injected into the mercury to suppress the pressure waves. The front end of the vessel was cut out to inspect the effect of the damage mitigation technologies on the interior surface. The results showed that the double-walled target facing the mercury with gas microbubbles operating at 1812 MWh for an average power of 434 kW had equivalent damage to the single-walled target without microbubbles operating 1048 MWh for average power of 181 kW. The erosion depth due to cavitation in the narrow channel was clearly smaller than it was on the wall facing the bubbling mercury