A Wonderwall.....? To withstand the intense heat of the fusion process, metals with a high melting point, such as tungsten, are used in the tokamak’s inner walls. However, tungsten can contaminate and dilute the plasma. Scientists found that by creating a particular type of ‘heat barrier’, in the form of a large temperature drop of 20 million degrees celsius, the tungsten contaminants are prevented from entering the core of plasma. Advances in technology - you've just got to Roll With It.