Pressure wave-induced cavitation erosion in narrow channel of stagnant mercury

Abstract

The pressure waves which is caused by high-intensity proton beam injection into mercury is a critical issue to keep the steady operation in the high-power spallation neutron source, because the pressure waves induces cavitation and imposes severe erosion damage on the target vessel due to bubble collapsing. A double-walled structure of the beam window portion is adopted for the advanced mercury target vessel in the Japan Proton Accelerator Research Complex (J-PARC). The double-walled structure which has the narrow gap between the inner and outer walls is expected to reduce cavitation erosion in the beam window portion by deforming the shape of cavitation bubbles due to the flowing and gap boundary effects. In order to understand the cavitation damage in the narrow gap, cavitation damage tests of the type 316 stainless steels were conducted using mechanically-induced pressure waves under stagnant mercury with parametrically changing gap width and machine power. Furthermore, numerical simulation was carried out to estimate the pressure and cavitation bubble behavior in the narrow channel. The results showed that the clear damage reduction which was attributed to the deformation of bubble collapse due to the channel wall boundary was confirmed. On the other hand, the damage in the narrow gap was not directly related to the imposed power. The severe damage caused by the secondary cavitation bubble collapse predicted through the numerical simulation was observed at the lowest power.

Keywords

• narrow channel
• cavitation erosion
• mercury
• spallation neutron source