Cavitation damage experiments for mercury spallation targets at the LANSCE – WNR in 2005

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.