Predictions of H-mode performance in ITER

Time-dependent integrated predictive modelling is carried out using the PTRANSP code to predict fusion power and parameters such as alpha particle density and pressure in ITER H-mode plasmas. Auxiliary heating by negative ion neutral beam injection and ion-cyclotron heating of He 3 minority ions are modelled, and the GLF23 transport model is used in the prediction of the evolution of plasma temperature profiles. Effects of beam steering, beam torque, plasma rotation, beam current drive, pedestal temperatures, sawtooth oscillations, magnetic diffusion and accumulation of He ash are treated self-consistently. Variations in assumptions associated with physics uncertainties for standard base-line DT H-mode plasmas (with I p = 15 MA, B TF = 5.3 T and Greenwald fraction = 0.86) lead to a range of predictions for DT fusion power P DT and quasi-steady state fusion Q DT (≡P DT /P aux). Typical predictions assuming P aux = 50–53 MW yield P DT = 250–720 MW and Q DT = 5–14. In some cases where P aux is ramped down or shut off after initial flat-top conditions, quasi-steady Q DT can be considerably higher, even infinite. Adverse physics assumptions such as the existence of an inward pinch of the helium ash and an ash recycling coefficient approaching unity lead to very low values for P DT. Alternative scenarios with different heating and reduced performance regimes are also considered including plasmas with only H or D isotopes, DT plasmas with toroidal field reduced 10% or 20% and discharges with reduced beam voltage. In full-performance D-only discharges, tritium burn up is predicted to generate central tritium densities up to 10 16 m −3 and DT neutron rates up to 5 × 10 16 s −1 , compared with the DD neutron rates of 6 × 10 17 s −1. Predictions with the toroidal field reduced 10% or 20% below the planned 5.3 T and keeping the same q 98 , Greenwald fraction and β n indicate that the fusion yield P DT and Q DT will be lower by about a factor of two (scaling as B 3.5).