Role of cavitation on Initiating Mercury-Steel Wetting

摘要

In accelerator-driven neutron sources such as the Spallation Neutron Source (SNS)with powers in the 2 MW range (time-averaged), the interaction of the energetic proton beam with the mercury target can lead to very high heating rates in the target. Although the resulting temperature rise is relatively small (a few degrees C), the rate of temperature rise is enormous (-10(sup 7) C/s) during the very brief beam pulse (-0.58 (micro)s). The resulting thermal-shock induced compression of the mercury leads to the production of large amplitude pressure waves in the mercury that interact with the walls of the mercury target and the bulk flow field. Understanding and predicting propagation of pressure pulses in the target are considered critical for establishing the feasibility of constructing and safely operating such devices. Safety-related operational concerns exist in two main areas, viz., (1) possible target enclosure failure from impact of thermal shocks on the wall due to its direct heating from the proton beam and the loads transferred from the mercury compression waves, and (2) impact of the compression-cum-rarefaction wave-induced effects such as cavitation bubble emanation and their impact on mercury-steel interfacial phenomena (such as wetting, mass transfer and erosion).