Progress in toroidal confinement and fusion research

During the past thirty years, the characteristic value of TinτE for toroidal confinement experiments has advanced by more than seven orders of magnitude. Part of this advance has been due to an increase of gross machine parameters. Most of the advance is associated with improvements in the quality of plasma confinement. The combined evidence of spherator and tokamak research clarifies the role of magnetic field geometry in determining confinement and points to the importance of shielding out plasma edge effects. A true physical understanding of anomalous transport remains to be achieved. Improvements in the architecture of the tokamak plasma edge have already served to decrease Gedge substantially in H-mode operation. Increases in the factor ncore/nedge have yielded similar benefits for TFTR supershots. This paper illustrates that toroidal confinement research, and particularly tokamak research, has made substantial progress towards its goal---even without the guiding light of a true physical understanding. The potential rewards for a rigorously scientific optimization of tokamak confinement, however, remain very large. Achieving ignition at a minimal plasma-current level will be the key to cost-effective steady-state operation (i.e., with noninductive current- drive); moderate reactor unit size and cost is a precondition for timely progress through the developmental phase of fusion power. One good way to achieve the desired quality of insight into the tokamak will be to pursue the search for a consistent overall physics of plasma transport in toroidal geometry