The perfect super tokamak device required high-displacement metal because the energy generated by fusion needed to be absorbed by an inner wall called a "cladding".
The "cladding", also known as the "first wall of the fusion reactor", was the inner wall directly exposed to the fusion reaction. What it had to face was plasma with a high temperature of tens of millions of degrees or even hundreds of millions of degrees, and a large amount of neutron radiation. The strength of the material depended on the arrangement of atoms. Under such extreme conditions, after the atoms were continuously bombarded, the performance of the material would soon deteriorate.