Confinement and transport studies of conventional scenarios in ASDEX Upgrade

Confinement studies of conventional scenarios, i.e, L and H modes. in ASDEX Upgrade indicate that the ion and electron temperature profiles are generally limited by a critical value of delT/T. When this is the case the profiles are stiff: core temperatures are proportional to pedestal temperatures. Transport simulations based on turbulence driven by all ion temperature gradient show good agreement with the ion experimental data for H modes, Studies specifically dedicated to electron transport using electron cyclotron heating with steady state and modulated powers indicate that the electron temperature profiles are also stiff. Candidates for turbulence having a threshold in delT(e)/T-e may be trapped electron modes and electron temperature gradient driven instabilities. The critical threshold (delT(e)/T-e)(c) and the increase of the stiffness factor with temperature are found experimentally. In contrast, the density profiles are not stiff, hut the variation in shape remains moderate in these conventional scenarios. As a consequence of this profile behaviour, the plasma energy is proportional to the pedestal pressure. The global confinement time increases with triangularity and can be good at densities close to the Greenwald limit at high triangularity. In this operational corner and at q(95) around 4, the replacement of large type I ELMs by small ELMs of type II provides good confinement with very reduced peak power load on the divertor plates. This regime is believed to be adequate for a fusion reactor.