However, the high requirements do not only concern temperature resistance alone. The plasma also proves to be extremely sensitive as regards contaminations so that the group of materials which may be used is also extremely small for this reason. Today, specially modified CFC material, which offers a favourable mixture of high temperature resistance, heat conductivity, mechanic load carrying ability and purity is primarily used in these applications.
Comprehensive experience in the use of carbon materials has been gathered in the field of nuclear reactors for many years. In these applications, water can be used instead of graphite as the moderator material which slows down the fast neutrons to thermal energy levels by hitting against its atomic nuclei. Large parts of the reactor consist of graphite components or are lined with graphite tiles. In this case, it is not only the type and concentration of contaminations which plays an important role but a good isotropy is also required. In pebble bed reactors both the moderator balls and the fuel balls are made from graphite. Moreover, soft or hard felt plates made of carbon fibres are also used in addition.