Comparison of high-mode predictive simulations using Mixed Bohm/gyro-Bohm and Multi-Mode (MMM95) transport models

Abstract

Two different transport models—the Mixed Bohm/gyro-Bohm [Joint European Torus (JET)] model [Erba et al., Plasma Phys. Controlled Fusion 39, 261 (1997)] and the Multi-Mode model (MMM95) [Bateman et al., Phys. Plasmas 5, 1793 (1998)]—are used in predictive transport simulations of 22 high-mode discharges. Fourteen discharges that include systematic scans in normalized gyroradius (ρ*), plasma pressure (β), collisionality, and isotope mass in the JET tokamak [Rebut et al., Nucl. Fusion 25, 1011 (1985)] and eight discharges that include scans in ρ*, elongation (κ), power, and density in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] are considered. When simulation temperature and density profiles are compared with processed experimental data from the International Profile Database, it is found that the results with either the JET or MMM95 transport model match experimental data about equally well. With either model, the average normalized rms deviation is approximately 10%. In the simulations carried out using the JET model, the component of the model with Bohm scaling (which is proportional to gyroradius) dominates over much of the plasma. In contrast, the MMM95 model has purely gyro-Bohm scaling (proportional to gyroradius squared). In spite of the differences in the underlying scaling of these transport models, both models reproduce the global confinement scalings observed in the scans equally well. These results are explained by changes in profile shapes from one end of each scan to the other. These changes in the profile shapes are caused by changes in boundary conditions, heating and particle source profiles, large scale instabilities, and transport.