Phenomenology of plasma-wall interaction using liquid metals in tokamak devices

The goal of the present thesis is to present the theoretical and experimental results concerning the use of liquid metal in tokamak devices. Most of the experimental work has been performed on FTU at the ENEA laboratories in Frascati. The main part of the work has consisted of analyzing the evolution of thermal loads, plasma contamination and plasma edge parameters variations determined by the exposure of liquid metal limiters. A radiative model is proposed to explain the vapor shield effect observed during the past experimental campaigns with the Liquid Lithium Limiter: the results of the simulations and the comparisons made with the experimental data are illustrated. Much time has been spent in the installation, debugging and exploration of two different limiters on FTU: the Cooled Lithium Limiter and the Liquid Tin Limiter. FTU was the first, and up to now unique, tokamak in the world operating with a liquid tin limiter. The results, supported by experimental data and simulations, are reported and discussed. Moreover, a comparison between lithium and tin experiments on FTU is presented. Part of the Ph.D. work has been dedicated to the study and the interpretation of the diagnostics deputy to the main plasma edge parameters measurements. Different Langmuir probes were designed and built for experiments in FTU and other devices too. The old FTU Langmuir probes acquisition system has been successfully moved to a new hardware, and a new software is now performing the data reconstruction. Another part of the work has concerned the implementation ex novo of a dedicated laboratory in Frascati focused on the liquid metal features studies, such as wettability, corrosion, and chemical-physical characteristics investigation of the fusion relevant liquid metals (lithium, gallium, and tin). A high vacuum oven was installed for this purpose, and the first test phase ended successfully. Furthermore, a small vacuum chamber was assembled allowing temperature up to 1500°C in a limited volume. This made it possible to increase the testing rate and ultimately to achieve the wetting of small-size tungsten CPS structures with both gallium and tin. In the present work an innovative tungsten coating processes, to avoid corrosion of the structural materials has been investigated. The studies conducted together with the University ”La Sapienza” and the ENEA Brasimone research center led to the validation and the realization of a solid and reliable tungsten deposit using the detonation gun machine. During the final period of the Ph.D., liquid tin samples analyses have been carried out after the plasma exposure on ISTTOK tokamak in Lisbon. The results obtained in the heat load calculation and tin effects on plasma are presented, together with a new proposal for the use of CPS-base samples. Finally, a work undertaken in collaboration with the INFN of Frascati and the CERN laboratory in Geneva is reported, regarding the possibility of using liquid lithium as a target for a particle accelerator for muon production