Impact of plasma, magnet and wall performances on tokamak and helical reactor economics

For the assessment of both tokamak and helical reactors, the base case reactor models are introduced, and parameter scan analyses on plasma beta, electric power output, maximum magnetic field strength and neutron wall loading are carried out. The assessment shows that high temperature operation is appropriate in tokamak reactors to increase bootstrap current fraction and current-drive (CD) efficiency. In contrast, low-temperature high-density operation is feasible and desirable in helical system to reduce helical ripple transport. The capital cost of helical reactors is rather high; however, the cost of electricity (COE) is not much higher than that of tokamak reactors especially in the case of low beta design, because of smaller re-circulation power (no current-drive power) and less-frequent blanket replacements due to lower neutron wall load. The engineering improvement of increasing maximum magnetic field strength gives rise to the compact designs with lower construction cost. However, it does not lead to the strong reduction in COE because of the increase in the neutron wall loading. The COE critically depends on the system availability which is determined by the wall lifetime and the blanket maintenance time.