Design of an economically attractive tokamak fusion reactor depends on producing steady-state plasma operation with simultaneous high energy density (β) and high energy confinement (τE); either of these, by itself, is insufficient. In operation of the DIII-D tokamak, both high confinement enhancement (H ≡ τE/τITER-89P = 4) and high normalized β (βN ≡ β/(I/aB) = 6%-m-T/MA) have been obtained. For the present, these conditions have been produced separately and in transient discharges. The DIII-D advanced tokamak development program is directed toward developing an understanding of the characteristics which lead to high stability and confinement, and to use that understanding to demonstrate stationary, high performance operation through active control of the plasma shape and profiles.

We have identified some of the features of the operating modes in DIII-D that contribute to better performance. These are control of the plasma shape, control of both bulk plasma rotation and shear in the rotation and Er profiles, and particularly control of the toroidal current profiles. In order to guide our future experiments, we are developing optimized scenarios based on our anticipated plasma control capabilities, particularly using fast wave current drive (on-axis) and electron cyclotron current drive (off-axis). The most highly developed model is the second-stable core VH-mode, which has a reversed magnetic shear safety factor profile [q(0) = 3.9, qmin = 2.6, and q95 = 6]. This model plasma uses profiles which we expect to be realizable. At βN ≥ 6, it is stable to n=1 kink modes and ideal ballooning modes, and is expected to reach H ≥ 3 with VH-mode-like confinement.