A liquid-mercury target system for the MW-scale target is being developed in the world. The pitting damage induced by pressure wave propagation gets to be one of critical issues to estimate the life of the target structure with mercury and to evaluate its structural integrity. The off-line test on the pitting damage at high cycles over 10 millions was carried out using a novel device, the MIMTM which drives electromagnetically to impose pulse pressure into the mercury. It was found from the pitting damage data obtained by the MIMTM and comparison with classical vibratory hone tests that the pitting damage can be characterized in two steps, an incubation period that can extend to 10 6 cycles in 20% cold worked 316SS and 10 7 cycles in surface hardening treated one and steady state erosion where mass loss scales with the number of cycles to approximately the 1.27 power for mercury. The length of the incubation period is primarily a function of the material and the intensity of the pressure. This observation provides a simple model for estimating lifetime for different materials and beam power.

In-beam experiments investigating cavitation damage in short pulse mercury spallation targets were performed at the Los Alamos Neutron Science Center -Weapons Neutron Research (LANSCE -WNR) facility in 2005. Two main areas were investigated. First, damage dependence on three mercury conditions -stagnant, flowing, and flowing with bubble injection -was investigated by employing a small mercury target loop with replaceable damage test specimens. One hundred beam pulses were passed through the loop mercury and specimen pair for each test condition. Damage with flowing mercury (V = 0.4 m/s) was less than half that which was incurred with stagnant mercury. Gas bubble injection added into the flow further reduced damage to about one-fourth that of stagnant mercury. Acoustic emissions from cavitation bubble collapse were concurrently measured on the exterior of the loop using a laser Doppler vibrometer and were correlated to the observed damage. The second area of experimentation was erosion rate dependence on proton beam intensity. Prior research had indicated that incubation-phase cavitation erosion rate is strongly dependent on beam intensity, by a power law with the exponent perhaps as large as 4. The 2005 results are inconsistent with earlier in-beam test results and do not support the power law dependence. This paper will provide a detailed description of the experiment, present results and discuss the findings. Published by Elsevier B.V.

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