ITER Steady-State Demonstration on DIII-D

A systematic scan of $q_{95}$ (=4.5, 5.5, 6.5) at constant $\beta_N$ ($\sim$3) and high $q_{min}$ ($\sim$1.8-2.1) has been obtained in a lower single null ITER-like shape to study confinement, stability and edge pedestal characteristics using off-axis neutral beam current drive for the ITER steady-state mission ($f_{NI}=1$, $Q=5$). The edge pedestal height is found substantially lower than in similar 2008 experiments, resulting in lower $f_{NI}$ due to reduced edge pedestal bootstrap current. Toroidal Alfv\'en Eigenmode power fluctuation is well correlated with the estimated beam ion diffusion (D$_b$). Strong dependency of D$_b$ on $q_{95}$, $q_{min}$ and neutral beam power (PNB) has been found indicating that lower $q_{95}$ ($\leq$4.5) would have reasonably good beam ion confinement (D$_b \geq 0.3\,$m$^2$/s) even at $q_{min}>2$ and high PNB=12 MW. The calculated ideal $\beta_N$ stability limit increases with lower $q_{95}$ allowing access to high $\beta_N$ ($>$3.5) needed for $f_{NI}=1$ and $Q=5$. This study shows that optimum choice of $q_{95}$ ($\sim$5.5) and $q_{min}$ ($>$2) is crucial to achieving $Q=5$ steady-state mission for ITER.