Generation of net electric power with a tokamak reactor under foreseeable physical and engineering conditions

This study reveals for the first time the plasma performance required for a tokamak reactor to generate net electric power under foreseeable engineering conditions. It was found that the reference plasma performance of the ITER inductive operation mode with beta(N) = 1.8, HH = 1.0, and fn(GW) = 0.85 had sufficient potential to achieve the electric break-even condition (net electric power P-e(net) = 0 MW) under the following engineering conditions: machine major radius 6.5 m less than or equal to R-p less than or equal to 8.5 m, the maximum magnetic field on TF coils B-tmax = 16 T, thermal efficiency eta(e) = 30%, and NBI system efficiency eta(NBI) = 50%. The key parameters used in demonstrating net electric power generation in tokamak reactors are beta(N) and fn(GW). beta(N) greater than or equal to 3.0 is required for P-e(net) similar to 600 MW with fusion power P-f similar to 3000 MW. On the other hand, fn(GW) greater than or equal to 1.0 is inevitable to demonstrate net electric power generation, if high temperatures, such as average temperatures of T-ave > 16 keV, cannot be selected for the reactor design. To apply these results to the design of a tokamak reactor for demonstrating net electric power generation, the plasma performance diagrams on the Q vs P-f (energy multiplication factor vs fusion power) space for several major radii (i.e. 6.5, 7.5, and 8.5 m) were depicted. From these figures, we see that a design with a major radius R-p similar to 7.5 m seems preferable for demonstrating net electric power generation when one aims at early realization of fusion energy.