Plasma Shape Optimization For Steady State Tokamak Development In Diii D

For a more detailed account of the results summarized here and for references, see C.T. Holcomb et al., Phys. Plasmas 16, 056116 (2009). Advanced tokamak research on DIII-D is focused on developing a high fusion gain, steady-state scenario that would eliminate or greatly reduce the demands on an inductive transformer in future machines. Steady-state operation requires the inductively driven current density (j{sub Ind}) be zero everywhere. Most of the total current I{sub p} is typically from self-driven bootstrap current, with the remainder driven by external noninductive sources, such as neutral beam and radiofrequency current drive. This paper describes an extension of the fully noninductive condition (f{sub NI} ≈ 100%) to ≈0.7 current relaxation times that was achieved by a combination of more available ECCD and new scientific insights. The insights are an optimization of performance through variation of the plasma shape parameter known as squareness ([zeta]) and an optimization of divertor magnetic balance. These optimizations simultaneously improve stability, confinement, and density control. These are each essential for achieving fully noninductive operation.