Inter-ELM behaviour of the electron density and temperature pedestal in ASDEX Upgrade

The behaviour of the recovery of the electron temperature and density during individual ELM (edge localized mode) cycles has been examined closely for a series of type I ELMy H-mode discharges with different fuelling levels and medium collisionality. A characterization of the typical ELM recovery cycle has been established. Distinct phases have been observed in the build-up of the plasma edge profiles after their relaxation caused by the ELM crash. A thorough evaluation of ELM-synchronized data has revealed that the recovery of the electron temperature and density pedestals are correlated. A new behaviour has been discovered in the build-up phase of the plasma edge, during which the temperature stagnates while the density profile steepens. It was found that in some cases the ELM is triggered immediately after the recovery of the pressure profile, consistent with the expectations from edge ballooning theory, while in other cases all edge profiles reached their final shape a long time before the next ELM occurred. The theory that a delayed edge current induces the actual crash could not be confirmed; the current diffusion seems only to play a minor role in the edge of the plasma.