Transport modeling of the DIII-D high βₚ scenario and extrapolations to ITER steady-state operation

In this study, transport modeling of a proposed ITER steady-state scenario based on DIII-D high poloidal-beta (βₚ ) discharges finds that ITB formation can occur with either sufficient rotation or a negative central shear q-profile. The high βₚ scenario is characterized by a large bootstrap current fraction (80%) which reduces the demands on the external current drive, and a large radius internal transport barrier which is associated with excellent normalized confinement. Modeling predictions of the electron transport in the high βₚ scenario improve as q₉₅ approaches levels similar to typical existing models of ITER steady-state and the ion transport is turbulence dominated. Typical temperature and density profiles from the non-inductive high βₚ scenario on DIII-D are scaled according to 0D modeling predictions of the requirements for achieving a $Q=5$ steady-state fusion gain in ITER with 'day one' heating and current drive capabilities. Then, TGLF turbulence modeling is carried out under systematic variations of the toroidal rotation and the core q-profile. A high bootstrap fraction, high βₚ scenario is found to be near an ITB formation threshold, and either strong negative central magnetic shear or rotation in a high bootstrap fraction are found to successfully provide the turbulence suppression required to achieve $Q=5$.