The potential minimum cost of electricity (COS) for superconducting tokamak power reactors is estimated by increasing the physics (confinement, beta limit, bootstrap current fraction) and technology [neutral beam energy, toroidal field (TF) coil allowable stresses, divertor heat flux, superconducting coil critical field, critical temperature, and quench temperature rise] constraints far beyond those assumed for ITER until the point of diminishing returns is reached. A version of the TETRA

more »

... s code, calibrated with the ITBR design and modified for power reactors, is used for this analysis, limiting this study to reactors with the same basic device configuration and costing algorithms as ITER. A minimum COE is reduced from >200 to about 80 mill/kWh when the allowable design constraints are raised to 2 times those of ITER. At 4 times the ITER allowables, a minimum COE of about 60 mill/kWh is obtained. The corresponding tokamak has a major radius of approximately 4 m, a plasma current close to 10 MA, an aspect ratio of 4, a confinement H-factor <3, a beta limit of approximately 2 times the first stability regime, a divertor heat flux of about 20 MW/m 3 , a 5ma> < 18 T, and a TF coil average current density about 3 times that of ITER. The design constraints that bound the minimum COB are the allowable stresses in the TF coil, the neutral beam energy, and the 99% bootstrap current (essentially free current drive).