Deuterium/Tritium fusion produces neutrons that will escape the magnetic fields and hit the surrounding machine producing heat but also damage. This shield around the machine absorbing the neutrons will have a circulating fluid that will remove the heat to run a steam or other type of generator.
We don't really know how to build this part of the reactor right now, but some metals have the ability to self heal and people think this shield should be possible to build that has a decent lifespan. This is a part of fusion reactors that could be researched right now in parallel with other problems, but there has not yet been funding to build a high level neutron source facility to do the research. This is one fact of many that shows, I think, that national governments are not really interested in fusion energy succeeding.
My father was a plasma physicist that researched controlled fusion and he told me that current neutron sources were not useful for this. I think was a combination of the energy spectrum of the neutrons, the flux power, and the physical size/shape of the target area.
