Impact erosion by pressure wave propagation in mercury target for pulsed spallation neutron source

Spallation neutron source facilities employing mercury targets, J-PARC in Japan and SNS in United States, are close to commissioning. Mercury as a spallation target is contained in a solid metal vessel. A pressure wave will be excited in the mercury by local explosive heating due to the injection of high-power proton beam. The pressure wave propagates in the mercury towards the inner surface of the vessel and gives it an impact load, which affects the safety of the target vessel. So called pitting damage can occur by the cavitation phenomenon induced with negative pressure at the liquid-solid interface. Pitting effect has been evaluated using the MIMTM (Magnetic Impact Testing Machine). Some properties of the pitting have been clarified and the technology for reducing the effects of pressure wave is under development. (K. Yoshida)