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This paper focuses on the development of the water-cooled divertor target concept known as Thermal Break, which was carried out in two phases. In Phase 1, six small scale mock-ups were fabricated and subjected to high heat flux (HHF) testing of up to 25 MW/m 2 and thermal cycling of up to 500 cycles at 20 MW/m 2. All six mock-ups survived the campaign and maintained 20 MW/m 2 heat exhaust capability. Detailed examination of mock-ups was carried out to understand the damage mechanisms. One mock-up, which was tested beyond its design intent at 500 cycles, shows signs of progressive damage. Potential damage modes were identified and influenced subsequent Phase 2 mock-up design. Although there are signs of tungsten surface cracking, the predominant damage mode is not by "deep cracking" but substantial permanent deformation in the interlayer features. Therefore, in Phase 2 the manufacturing procedure was updated, the interlayer grooves were given stress-relieving radii which have significantly reduced the interlayer plastic strain range. Interlayer design parameters were selected following the use of response surface-based design search and optimization. Mock-ups of the Phase 2 design have been manufactured and HHF testing is planned within 2018.

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Power exhaust is a key mission in the roadmap to the realization of a future fusion reactor. Among the different solutions, the use of liquid metals as plasma facing materials are of interest due to their potential increased lifetime. Several liquid metal limiters have been successfully tested in the Frascati Tokamak Upgrade over the last 10 years. Liquid materials such as lithium and tin have been investigated using capillary porous systems (CPSs), and their impact on plasma performance has been explored. From such experience, a liquid metal divertor (LMD) concept design, CPS-based, is here proposed. Tin has been preferred as plasma facing material. The proposed LMD would operate, in low evaporative regime, with matching heat exhausting capabilities to those of the baseline ITER-like divertor. Continuous refilling of the CPS is guaranteed with a reservoir at the back of the unit, where the metal is kept liquid through a gas heating circuit. The study has been carried out using ANSYS and the thermal results will be shown. All the design choices are compatible with the current materials and the constraints adopted for the DEMO W divertor. Using such configuration, thermal loads up to 20 MW/m2 are exhausted while keeping the surface temperature below 1250 °C. The design foresees values of pressure, temperature and flow rate of the water coolant in the same range expected for the W DEMO divertor, thus facilitating the integration of such solution in the current cassette design. Technological and practical aspects are addressed, i.e. tin corrosion and CPS wettability. Possible solutions to prevent tin corrosion, and its compatibility with structural materials, will be outlined.