Improvement to Tokamak fusion reactor design using optimized inner TF coil structure and conductor grading: Higher B, lower A, more compact

Recently, an optimal radial grading of structure and conductor of the inner leg of a Tokamak toroidal field coil was found by applying calculus of variations to an axisymmetric plane strain model. The optimal profile consists of an outer winding pack with just enough structure to support the accumulated radial force (not wedged), and an inner bucking cylinder which has been micro-structured so that its radial compliance assumes a specific profile. This inner bucking cylinder in particular is a significant advance, allowing up to 40% higher magnetic field. This improvement has a complex effect on the optimal Tokamak fusion reactor design point, rippling through plasma physics and engineering constraints such as the beta limit, recirculating power fraction, and neutron wall load. The result is that the fusion reactor can be made more compact and/or higher power than would be otherwise possible.