Levitated dipole fusion reactors confine plasma in the magnetic field of a superconducting coil floating inside the vacuum vessel. The geometry is elegant — the confining magnet is decoupled from the vessel walls, making the reactor accessible, maintainable, and potentially cheap to operate. But deuterium-tritium fuel produces neutrons, and neutrons damage superconducting magnets. Previous designs avoided DT altogether, accepting lower fusion yields to protect the magnet.
Simpson and colleagues (arXiv:2602.20564) solve this differently. Instead of avoiding neutron damage, they design for it. The REBCO core magnet is heavily shielded — alternating tungsten and boron carbide layers radiate 92% of absorbed heat to the first wall while attenuating neutrons sufficiently. But the innermost 20% of the coil — the portion closest to the plasma — is designated as sacrificial. It will accumulate neutron damage and be replaced annually.
The sacrificial section is designed for replacement: modular, removable, refurbishable. The remaining 80% of the magnet is protected well enough to last the reactor's lifetime. The 23-Tesla field is maintained by the full coil, but the design tolerates the inner section degrading. Replace the damaged part; keep the rest.
The two prototype plants produce 667 MW of fusion power and 208 MW of net electricity. The economics work because the sacrificial replacement is cheap relative to building an entirely damage-proof magnet — which may not be possible at all for DT conditions.
The general principle: when a system component faces inevitable degradation from the environment it operates in, designing it as expendable and replaceable can be more effective than designing it as permanent and resistant. Accept the damage; localize it; replace the damaged part. Sacrifice enables function that protection cannot.