Theory-based transport modeling of the gyro-radius experiments

Abstract

Self‐consistent predictive transport simulations of temperature and density profiles have been carried out for ten dimensionally similar low (L) mode discharges from the Tokamak Fusion Test Reactor (TFTR) [D. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)], Doublet III‐D Tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], and the Joint European Torus [P. H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 (1985)], where only the normalized Larmor radius was allowed to vary. It is found that a purely gyro‐Bohm transport model predicts temperature and density profiles that match the experimental data from these ρ_* scans very well. In particular, a combination of theoretically derived transport models is used in these simulations, including the Weiland model for transport due to drift waves (ion temperature gradient and trapped electron modes) and the Guzdar–Drake model for transport due to resistive ballooning modes. These gyro‐Bohm transport models depend very sensitively on the shapes as well as the magnitudes of the profiles. As the magnetic field, density and temperature are changed in each dimensionally similar series of discharges, the penetration length of neutrals from the edge varies considerably. This effect causes the shape of the density profiles to change near the edge of the plasma, which causes the scaling of our transport model diffusivities to differ significantly from their fundamentally gyro‐Bohm scaling.