Experiments on FTU with a liquid tin limiter

A capillary porous liquid tin limiter (TLL) was exposed as a plasma-facing component (PFC) in the Frascati Tokamak Upgrade. The TLL was progressively inserted deeper into the scrape-off-layer, very close to the last closed magnetic surface (<0.5 cm). Spectroscopic measurements, a fast IR camera, and Langmuir probes monitored the evolution of tin emission, tin surface temperature, and heat loads on the limiter. The surface temperature rose up to 1700 degrees C in the hottest limiter region, a value for which tin evaporation is very high. Heat loads in excess of 18 MW m(-2) were withstood by the TLL. Numerical simulations performed with the ANSYS code were in agreement with the experimental data, taking into account the heat load deposition profile on the TLL. As long as the surface temperature of the tin limiter is below 1300 degrees C, the main tin production mechanism is sputtering and the presence of such impurity in the discharge is negligible. When evaporation becomes dominant beyond 1300 degrees C, tin is the main impurity present in the plasma. Nevertheless, the concentration of tin is on the order of 5 x 10(-4) of the electronic density, and no degradation in plasma performance has been observed. These results are an important experimental confirmation of the possibility to use liquid metals as a PFC solution to the power exhaust for a fusion power plant.