Design measures to counteract pressure wave effects in the liquid metal target META:LIC

The liquid metal target concept META:LIC (MEgawatt TArget:Lead bIsmuth Cooled) is considered as a comparative target option for the long pulse spallation neutron source ESS (European Spallation Source). MW-class proton bombardment of liquid metal can result in pressure waves that impact the structure of the target. An analytical and a thermo-mechanical analysis with ANSYS CFX/LS-DYNA is performed. For the analytical analysis a modified Joukowsky equation to approximate the thermally induced peak pressure at the beginning of the pulse is introduced. The analysis indicates that the stressing of the target container due to pressure pulses initiated at the beginning and end of each pulse is less important compared to the stressing due to integral thermal expansion of the fluid during the full pulse period. Additionally, it is shown that a ramped proton pulse reduces the maximum pressure at the beginning of a pulse. Dedicated design measures to prevent high stresses and cavitation on the target container are described. These design measures include an expansion volume and a spoiler enforcing flow detachment. Internal free surfaces in the target module are created. The feasibility of stable internal free surfaces is confirmed by CFD simulations, however an experimental confirmation is mandatory.