Fluid turbulence simulations of ELM characteristics and divertor heat load for ITER scenarios using BOUT++

The BOUT++ code is used to simulate the ITER 11.5MA hybrid scenario and comparisons are made among ITER baseline, hybrid and steady-state operation (SSO) scenarios. Peeling-ballooning instabilities with different toroidal mode numbers dominate in different scenarios and consequently yield different types of ELMs. The energy loss fractions (DW/W_ped) in the baseline and hybrid scenarios are large (~10-20%) while the one in the SSO scenario is dramatically smaller (~1%), which are consistent with the features of type-I ELMs and grassy ELMs. The divertor heat flux width in the 3 scenarios given by the simulations is larger than the estimations based on the HD model and Eich scaling. The toroidal gap edge melting limit of tungsten monoblocks of divertor targets imposes constraints on ELM energy loss, giving that the ELM energy loss fraction should be smaller than 0.4%, 1.0%, and 1.2% for ITER baseline, hybrid and SSO scenarios. The simulations show that only the SSO scenario with grassy ELMs may satisfy the constraint. From transport simulations, we obtain the critical diffusivity χ_c=0.5m²/s  in 5MA/1.77T PFPO-1 scenario and χ_c=0.3m2/s in 7.5MA/2.65T PFPO-2 scenario for a transition from a drift to turbulence dominant regime.