Mitigation of Cavitation Damage in J-PARC Mercury Target Vessel

The target vessel, which enclosing liquid mercury, for the pulsed spallation neutron source at the JPARC is severely damaged by 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 target vessel. In addition, gas microbubbles are injected into the mercury to suppress the pressure waves. The narrow channel disturbs the growth of cavitation bubbles due to the pressure gradient. After finishing service operation, the front end of the target vessel was cut out, allowing us to inspect the effect of these cavitation damage mitigation technologies on the interior surface. The damage depth of the cutout specimens was quantitatively investigated by the replica method. The results showed that the erosion depth due to cavitation in the narrow channel is clearly smaller than on the wall facing mercury with injecting gas microbubbles.