Molybdene tiles of first wall panels inside Alcator C-Mod tokamak. (Source: Wikipedia.org)

The so-called plasma facing component, a part of the inner wall of the vacuum chamber that will be in direct contact with the plasma. The vacuum vessel in a tokamak usually has several layers. The innermost one is called the first wall and is in direct contact with the plasma. It must be able to withstand intense heat fluxes and particle bombardment, while not releasing impurities or absorbing tritium. In principle, it resembles the carbon-tiles that protect the Space Shuttle during its passage through the atmosphere. Also in the tokamak, these are separate plates that can be replaced if damaged. First wall panels are made of high melting point materials (e.g. beryllium, molybdenum, graphite).