Summary of cavitation erosion investigations for the SNS mercury target

Intense proton beam-induced heating of the spallation neutron source mercury target will cause pressure spikes that lead to the formation of cavitation bubbles in the mercury. Erosion of the mercury container walls caused by violent collapse of bubbles could potentially limit its service lifetime. In-beam tests for a limited number of pulses (<1000 pulses for each test target) have demonstrated that pitting damage appears to be especially sensitive to beam intensity, surface treatment, and gas injection. Using results of off-line pressure pulse tests conducted for a million cycles or more to scale the results from limited in-beam tests, it is concluded that the mercury target will last at least two weeks at a time-averaged proton beam power level of 1 MW. However, because of remaining uncertainties, it is concluded that further research and development and target design efforts are needed to verify these conclusions and extend the target to higher operating powers and longer lifetimes.