Temperature control of the FTU Liquid Lithium Limiter

Several experiments on Tokamak devices have shown serious difficulties in the development of appropriate technical solutions concerning the structure and material composition of the plasma-facing elements. For instance the first wall (i.e. the innermost surface of the Tokamak vacuum chamber), the limiters and the divertors are a main concern due to the neutron flux and the thermal loads. A possible solution is to abandon solid plasma facing materials, using liquid metals instead. In the FTU (Frascati Tokamak Upgrade) an experimental Liquid Lithium Limiter (LLL) has been installed and tested, by empirically tuning the plasma position in order to prevent the modules of the limiter from reaching critical temperatures. In this paper we propose two alternative nonlinear control strategies for the temperature regulation of the surfaces of the LLL modules. The paper is concluded with numerical simulations that validate the performances of the proposed approaches.