SUMMARY

Fusion power excursions resulting from the strong positive temperature dependence of the D-T fusion rate would have significant consequences for heat removal in ITER and subsequent tokamaks. While several active power excursion control mechanisms have been and continue to be investigated, the impending operation of ITER provides a strong incentive to investigate the possibility of physical mechanisms and configurations that would inherently limit incipient power excursions. To this end, a computationally efficient predictive model has been developed that adjusts confinement characteristics based on results from regression analyses of DIII-D data.

While the ITER-98 law represents a correlation of data from a wide range of tokamaks, confinement scaling laws will need to be fine tuned to specific operational features of specific tokamaks in the future. A methodology for developing, by regression analysis, tokamak- and configuration-specific confinement tuning models is presented and applied to DIII-D as an illustration. It is shown that inclusion of tuning parameters in the confinement models can significantly enhance the agreement between simulated and experimental values relative to simulations in which only the ITER-98 scaling law is used. These confinement tuning parameters can also be used to investigate the effects of various heating sources and other plasma operating parameters on overall plasma performance and may be used in future studies to inform the selection of plasma configurations that are more robust against power excursions.