Pitting damage by pressure waves in a mercury target

Liquid-mercury target systems for MW-scale pulsed spallation neutron sources are being developed. A proton beam will be injected into the mercury target to induce spallation reactions. The moment the proton beam bombards the target, pressure waves will be generated in the mercury by the thermally shocked heat deposition. Negative pressures will cause the formation of short-lived cavities in the mercury. Those cavities that collapse on the interface between the mercury and the target vessel wall will develop pits in the wall surface. In order to investigate the pitting damage due to large numbers of cycles up to 10 million, the pressure waves were simulated electromagnetically in a Magnetic IMpact Testing Machine (MIMTM). The obtained data were compared with erosion data from classical vibratory horn tests and a bubble dynamic simulation was carried out to investigate the repeated frequency effect. It is demonstrated that the mean depth of erosion is predictable using a homologous line in the steady state with mass loss independent of testing machines. The incubation period is shown to depend on materials, repeated frequency and imposed power or pressure.