Distribution of microbubble sizes and behavior of large bubbles in mercury flow in a mockup target model of J-PARC

Haga, Katsuhiro  ; Naoe, Takashi   ; Kogawa, Hiroyuki  ; Kinoshita, Hidetaka   ; Ida, Masato; Futakawa, Masatoshi  ; Riemer, B.*; Wendel, M.*; Felde, D.*; Abdou, A.*

Microbubble injection into mercury is one of the prospective technologies to mitigate the pressure wave which causes the cavitation damage on the mercury target vessel wall of J-PARC. As one of the studies for the mercury target design with bubbling system, we carried out the mercury loop tests using a mockup model of the target vessel. Injected microbubbles in contact with the transparent top wall were observed to know the bubble size and distribution. As a result, bubbles in the range of radius from 10 to 150 microns, which are the ideal size for our purpose to suppress the pressure wave were transported to the beam window, where the bubbles should be distributed. It was found that the bubbles larger than 150 micron in radius were removed from the distribution by bubble buoyancy, and only the smaller bubbles could be transported downstream. The attention to the effect of bubbles on the cooling performance of the target vessel was raised by the experiment.