Transport simulations of ITER with empirical heat diffusivity scaling

Radiative mantle scenarios of the ignited ITER Engineering Design Activity (EDA) with argon and neon influxing are explored by computer experiments using special versions of the 1.5 dimensional (1.5-D) BALDUR predictive transport code. An empirical scaling law for the effective heat diffusivity, compatible with the ITERH92-P ELMy H mode scaling and validated against experiments, is applied. The prescribed flat density profiles, conductive heat loss across the separatrix of 200 MW and ratio τ*_He/ τ_E,r of 10 are reached in the simulations. Self-sustained thermonuclear burn is achieved for at least 485 s. The helium ash concentrations of up to 9.5% are found to cause significant fuel dilution. Owing to the high electron density, only small argon and neon fractions of 0.07 and 0.27%, respectively, are needed. In the argon scenario, the required radiation corrected thermal energy confinement time τ_E,r is 4.8 s. The confinement time predicted by the local scaling law is 1.4 times longer and agrees with the global scaling prediction. With argon, the design parameters are reached by radiating 128 MW within the separatrix, thus reducing the energy flow to the divertor to 73 MW. In the neon case with its more peripheral radiation, the radiative loss within the separatrix has to be diminished. Owing to the flat profile of the fuel ion density, the neoclassical drift velocities of argon and neon are directed outwards in the whole plasma. In the argon scenario, the sensitivity of transport to the density profile shape is studied. It is found that τ_E,r remains almost unchanged, varying between 4.5 and 4.8 s, which is explained by an analytic expression for the thermal energy. Peaking of the electron and impurity densities does not alter the required argon concentration but causes a peaking of the radiation profiles and reduction in the temperatures. Sufficiently narrow fuel ion density profiles are shown to cause inward directed neoclassical drift velocities of argon in the collisionless plasma. The minimum density for steady state operation at the designed alpha particle heating power, still compatible with the transport predicted by the heat diffusivity scaling, is found to be ⟨n_e⟩ = 9.1 × 10¹⁹ m^-3.