Predictive transport simulations of jet L and H mode gyro-radius scaling experiments

Predictive transport code simulations of gyro-radius scaling experiments have been performed using experimental data from JET profile databases. Both L mode and H mode discharges are considered. Self-consistently derived steady state profiles of electron and impurity density, temperatures and heat diffusivities are compared with the experimental profiles. The simulations are based on a first principle gyro-Bohm transport model for ion temperature gradient (ITG) modes, impurity modes and collisionless trapped electron (CTE) modes. In the good confinement region, the experimental profiles as well as the transport scalings are well reproduced by the simulations. In particular, apparent Bohm-and Goldston-like scalings of the local diffusivities are obtained in the L mode simulations, whereas gyro-Bohm scalings are obtained in the H mode scans. The scalings obtained in the L mode simulations are a result of small systematic deviations in the similarity conditions between the low field and high field discharges. In the H mode simulations, the profile effects are generally smaller, resulting in a gyro-Bohm scaling of the heat diffusivities. Since profile effects arise through the edge boundary conditions, the different scalings obtained in the simulations are attributed to differences in edge confinement between L and H mode plasmas.