Forthcoming Break-Even Conditions of Tokamak Plasma Performance for Fusion Energy Development

抄録

The present study reveals forthcoming break-even conditions of tokamak plasma performance for the fusion energy development. The first condition is the electric break-even condition, which means that the gross electric power generation is equal to the circulating power in a power plant. This is required for fusion energy to be recognized as a suitable candidate for an alternative energy source. As for the plasma performance (normalized beta value Β_N), confinement improvement factor for H-mode HH, the ratio of plasma density to Greenwald density fn_GW), the electric break-even condition requires the simultaneous achievement of 1.2 < Β_N < 2.7, 0.8 < HH, and 0.3 < fn_GW < 1.1 under the conditions of a maximum magnetic field on the TF coil B_tmax = 16 T, thermal efficiency η_e = 30 %, and current drive power P_NBI < 200 MW. It should be noted that the relatively moderate conditions of Β_N ˜ 1.8, HH ˜ 1.0, and fn_GW ˜ 0.9, which correspond to the ITER reference operation parameters, have a strong potential to achieve the electric break-even condition. The second condition is the economic break-even condition, which is required for fusion energy to be selected as an alternative energy source in the energy market. By using a long-term world energy scenario, a break-even price for introduction of fusion energy in the year 2050 is estimated to lie between 65 mill/kWh and 135 mill/kWh under the constraint of 550 ppm CO₂ concentration in the atmosphere. In the present study, this break-even price is applied to the economic break-even condition. However, because this break-even price is based on the present energy scenario including uncertainties, the economic break-even condition discussed here should not be considered the sufficient condition, but a necessary condition. Under the conditions of B_tmax = 16 T, η_e = 40 %, plant availability 60 %, and a radial build with/without CS coil, the economic break-even condition requires Β_N ˜ 5.0 for 65 mill/kWh of lower break-even price case. Finally, the present study reveals that the demonstration of steady-state operation with Β_N ˜ 3.0 in the ITER project leads to the upper region of the break-even price in the present world energy scenario, which implies that it is necessary to improve the plasma performance beyond that of the ITER advanced plasma operation.