Effects of pitting damage on fatigue limit and lifetime in mercury target

High power spallation targets for neutron source are being developed in the world. Mercury target will be installed at the material and life science facility in J-PARC, which will promote innovative science. The moment the proton beams bombard the mercury target, pressure waves will be generated in mercury by thermally shocked heat deposition. Cavitation will be induced through the pressure wave propagation in the mercury and erode the vessel inner surface contacting with mercury, i.e. pitting damage. The eroded vessel wall is damaged by cyclic fatigue because pulsed proton beams strike the target repeatedly. It is, therefore, important to evaluate the fatigue strength of the eroded vessel wall from the viewpoint of target lifetime estimation. In the paper, we describe the effects of pitting damage, cyclic fatigue damage and mercury environment on the lifetime of the mercury target.