Fusion Science and Technology / Volume 44 / Number 3 / November 2003 / Pages 618-635
Technical Paper / ASDEX Upgrade
The studies carried out in ASDEX Upgrade on transport in conventional scenarios are presented. The well-known property of tokamak temperature profiles being resilient is investigated in and interpreted, for both ions and electrons, as due to the existence of an inverse critical gradient length below which transport is low and above which it increases. Experiments in H-mode with different heating power deposition profiles were carried out. Simulation results of a variety of H-mode plasmas with three different transport models based on the physics assumptions that include the existence of such a threshold confirm this hypothesis. However, the profiles are not extremely stiff and can significantly deviate from the critical value. Electron heat transport was investigated in various experiments using electron cyclotron heating combining steady-state and power modulation. A variation of the electron heat flux while keeping the edge flux constant allows measurement of the threshold and the properties of electron transport. These resilience properties lead to a correlation between core and edge and to a dependence of global confinement on the pedestal energy. This is quantified in the analyses of a database that yield expressions linking edge and global confinement.