Localized-impact damage caused by proton bombarding in mercury target

A liquid-mercury target system for the MW-scale target is being developed in the world. The moment the proton beams bombard the target, stress waves will be imposed on the beam window and pressure waves will be generated in the mercury by the thermally shocked heat deposition. Provided that the negative pressure generates through its propagation in the mercury target and causes cavitation in the mercury, there is the possibility for the cavitation bubbles collapse to form pits on the interface between the mercury and the target vessel wall. In order to estimate the cavitation erosion damage off-line tests were performed using Split Hopkinson Pressure Bar (SHPB) technique. It was confirmed through the experiments that the pitting damage is suppressed by surface hardening treatments: Kolsterising, coatings, etc. Relative hardness appears to be a good correlating parameter on impact erosion resistance evaluated by the SHBP and conventional vibratory hone tests.