Turbulent optimization of toroidal configurations

Recent progress in ‘turbulent optimization’ of toroidal configurations is described, using a method recently developed for evolving such configurations to ones having reduced turbulent transport. The method uses the GENE gyrokinetic code to compute the radial heat flux Q_gk, and the STELLOPT optimization code with a theory-based ‘proxy’ figure of merit Q_pr to stand in for Q_gk for computational speed. Improved expressions for Q_pr have been developed, involving further geometric quantities beyond those in the original proxy, which can also be used as ‘control knobs’ to reduce Q_gk. Use of a global search algorithm has led to the discovery of turbulent-optimized configurations not found by the standard, local algorithm usually employed, as has use of a mapping capability which STELLOPT has been extended to provide, of figures of merit over the search space. (paper)