MYRRHA spallation target design

The high spallation efficiency, the high power density and stringent space limitations lead to the choice for a windowless liquid-metal spallation target. A free-surface flow is created, which convectively removes the heat deposited by the proton beam. The free surface is in direct contact with the vacuum beam line and the beam directly interacts with the liquid metal surface. This poses the problem of vacuum compatibility: evaporation from the surface should be avoided to not jeopardize the beam vacuum and to retain radio-active spallation products within the bulk material. Another issue is the definition and the free-surface flow stability in normal and transient (e.g. beam trip) conditions. The liquid-metal free surface is defined by the nozzle and feeder design and kept at a pre-defined position that is monitored by the LIDAR system. The spallation target is the most demanding part of the spallation loop.

A target design with window was studied in the MEGAPIE project. Its feasibility was demonstrated for low-intensity proton beams. For the beam intensities in MYRRHA, a window target would result in unacceptable low lifetimes and high unreliability.