shielding is the material layering in a 📝fusion machine that protects its magnets, structures, and the people around it from neutron and gamma radiation.
Shielding is distinct from the blanket it usually sits behind, and the distinction is one of purpose: the 📝blanket captures the energy of fusion neutrons productively — converting it to heat and breeding 📝tritium — while shielding simply attenuates what gets through, sacrificing itself so that nothing behind it is damaged. The neutrons at issue are the 14 MeV products of the 📝D-T reaction, which sail through magnetic fields unaffected; the layered answer combines dense metals such as steel and 📝tungsten to scatter fast neutrons and stop gamma rays, hydrogen-rich material such as water to slow neutrons down, and boron compounds to absorb them once slowed.
In a magnetically confined machine the most demanding customer is the magnet set: superconductors tolerate only a small lifetime dose and a small nuclear heating load at cryogenic temperature, so the shield's thickness is set by what the coils can bear. That thickness occupies the space between 📝plasma and coil and therefore drives the size of the whole machine — one reason compact high-field designs treat every centimeter of shield as precious, and why shielding, though passive, is a first-order design variable rather than an afterthought.