TRANSPORT SIMULATIONS OF ITER WITH EMPIRICAL HEAT DIFFUSIVITY SCALING

Radiative mantle scenarios of the ignited ITER Engineering Design Acti vity (EDA) with argon and neon influxing are explored by computer expe riments using special versions of the 1.5 dimensional (1.5-D) BALDUR p redictive transport code. An empirical scaling law for the effective h eat diffusivity, compatible with the ITERH92-P ELMy H mode scaling and validated against experiments, is applied. The prescribed hat density profiles, conductive heat loss across the separatrix of 200 MW and ra tio tau(He)/tau(E,r) of 10 are reached in the simulations. Self-susta ined thermonuclear burn is achieved for at least 485 s. The helium ash concentrations of up to 9.5% are found to cause significant fuel dilu tion. Owing to the high electron density, only small argon and neon fr actions of 0.07 and 0.27%, respectively, are needed. In the argon scen ario, the required radiation corrected thermal energy confinement time tau(E,r) is 4.8 s. The confinement time predicted by the local scalin g law is 1.4 times longer and agrees with the global scaling predictio n. With argon, the design parameters are reached by radiating 128 MW w ithin the separatrix, thus reducing the energy how to the divertor to 73 MW. In the neon case with its more peripheral radiation, the radiat ive loss within the separatrix has to be diminished. Owing to the hat 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 i s studied. It is found that tau(E,r) remains almost unchanged, varying between 4.5 and 4.8 s, which is explained by an analytic expression f or the thermal energy. Peaking of the electron and impurity densities does not alter the required argon concentration but causes a peaking o f the radiation profiles and reduction in the temperatures. Sufficient ly narrow fuel ion density profiles are shown to cause inward directed neoclassical drift velocities of argon in the collisionless plasma. T he minimum density for steady state operation at the designed alpha pa rticle heating power, still compatible with the transport predicted by the heat diffusivity scaling, is found to be (n(e)) = 9.1 x 10(19) m( -3).