First validation experiments for the radar-based diagnostic system of the IFMIF-DONES lithium target

The IFMIF-DONES (International Fusion Materials Irradiation Facility – DEMO Oriented Neutron Source) is designed to reproduce neutron irradiation conditions in a fusion reactor. In this setup, a 5 MW deuteron beam collides with a liquid lithium target flowing at 15 m/s and maintained at 300 °C. The resulting deuteron-lithium stripping reactions produce high flux neutrons with an energy spectrum comparable to that of future fusion reactors, thereby enabling testing of fusion-relevant materials, under controlled and homogenous conditions. A key component of this facility is the target assembly, where the ion beam interacts with the free surface of the liquid lithium target, which must maintain a thickness of 25 ± 1 mm to safely absorb the beam energy and minimize the neutron flux losses. This region of the facility is subjected to intense radiation, high temperatures, and lithium evaporation, making real-time diagnostics a challenging task. To address this hazard conditions, a radar-based system operating in the millimeter-wave (mmWave) range has been proposed. This system is able to continuously monitor the lithium thickness and to detect flow instabilities, interfacing with the Machine Protection System (MPS) to enable fast beam shutdown if the critical thickness is compromised. For initial technology feasibility tests, a commercial radar kit operating in the same frequency range planned for IFMIF-DONES has been acquired. Preliminary experiments include static-target tests that evaluate distance accuracy and material reflection characteristics using metallic and dielectric plates, followed by dynamic-target tests using water and liquid metals to simulate possible disturbances in the lithium flow. These experiments will validate the technology viability proposed as a solution for the fast MPS system and for quick monitoring of the Li surface homogeneity before implementing it in a real liquid lithium loop of IFMIF-DONES facility.