A study regarding the optimal radial build of a low-aspect-ratio tokamak fusion system

Highlights: • System parameters and the optimal radial build of a low-aspect-ratio tokamak fusion system were found. • Cases with a smaller aspect ratio yielded better tritium breeding capability than for the case with a larger aspect ratio. • The HCSB concept demonstrated the best tritium breeding capability and allowed smaller system size for the LAR tokamak fusion system. - Abstract: System parameters and the optimal radial build of a low-aspect-ratio (LAR) tokamak fusion system were found through the coupled analysis of a tokamak system and neutron transport. In a configuration with only an outboard breeding blanket, the minimum major radius to produce a given fusion power was determined by the shielding requirements and the magnetic field at the toroidal field (TF) coil. With a confinement enhancement factor H = 1.4, Q > 10 was possible for fusion power greater than 800 MW with an aspect ratio of A = 1.5; however, Q > 10 was possible for fusion power greater than 1800 MW with an aspect ratio of A = 2.0. The outboard radial build was determined by the tritium breeding and shielding requirements. The tritium breeding capability of blanket concepts proposed for testing in the International Thermonuclear Experimental Reactor (ITER) was evaluated by varying the outboard blanket thickness and the degree of lithium-6 (Li-6) enrichment. Cases with a smaller aspect ratio exhibited better performance since the number of fusion neutrons that contributed to tritium breeding were larger than the case with a larger aspect ratio. Among the blanket concepts, a helium (He)-cooled solid breeder (HCSB) concept showed the best tritium breeding capability and thus allowed for a smaller system size.