Transport at high β_p and development of candidate steady state scenarios for ITER

On DIII-D, the high β_N scenario has an internal transport barrier (ITB), ∼ β_p ∼ 3, q₉₅ ∼ 10, and very high normalized confinement H_98y2 ∼ 1.6. Recently, plasmas starting with these conditions have been dynamically driven to q₉₅ ∼ 6 and β_p ∼ 2, where we find the ITB and high performance persist for five energy confinement times. These conditions are projected to meet the ITER steady-state goal of Q = 5. The ITB is maintained at lower β_p with a strong reverse shear, consistent with predictions that negative central shear can lower the β_p threshold for the ITB. There are two observed confinement states in the high β_p scenario: H-mode confinement state with a high edge pedestal, and an enhanced confinement state with a low pedestal and an ITB. It has been observed in a scan of external resonant magnetic perturbation amplitude that when there are no large type-I ELMs, there is no transition to enhanced confinement. This is consistent with the proposed mechanism for ITB formation being a type-I ELM. Quasilinear gyro-Landau fluid predictive modeling of ITER suggests that only a modest reverse shear is required to achieve the ITB formation necessary for Q = 5 when electromagnetic physics including the kinetic ballooning mode (KBM) is incorporated.