Confinement studies of conventional scenarios, i.e. L and H modes, in ASDEX Upgradeindicate that the ion and electron temperature profiles are generallylimited by a critical value of ∇T/T. When this is the case the profilesare stiff: core temperatures are proportional to pedestal temperatures.Transport simulations based on turbulence driven by an ion temperature gradient showgood agreement with the ion experimental data for H modes.Studies specifically dedicated to electron transport using electron cyclotron heating with steady stateand modulated powers indicate that the electron temperature profiles are also stiff. Candidates for turbulence having a threshold in ∇Te/Te may be trapped electron modesand electron temperature gradient driven instabilities. The critical threshold (∇Te/Te)c and the increase of the stiffness factor with temperature are found experimentally.In contrast, the density profiles are not stiff, but the variation in shape remains moderate in these conventional scenarios.As a consequence of this profile behaviour, the plasma energy is proportionalto the pedestal pressure. The global confinement time increases with triangularity and can be good at densitiesclose to the Greenwald limit at high triangularity. In this operational corner and atq95 around 4, the replacement of large type I ELMs by small ELMs of type IIprovides good confinement with very reduced peak power load on the divertor plates.This regime is believed to be adequate for a fusion reactor.
Reduced electron thermal transport in low collisionality H-mode plasmas in DIII-D and the importance of TEM/ETG-scale turbulence