Pedestal and Scrape Off Layer Dynamics in ELMy H-mode Plasmas in JET
Pedestal and Scrape Off Layer (SOL) dynamics due to Edge Localised Modes (ELMs) have been studied on JET with improved diagnostic capability. The new High Resolution Thomson Scattering system enables detailed measurement of the space and time evolution of the Te and ne pedestal profiles. The pedestal and SOL dynamics for Type I ELMy H-mode plasmas has been studied for a wide range of plasma conditions. During a short period of <200ms after the ELM event radial profiles of filaments in the SOL electron density and temperature have been observed. After that period the SOL density is increased and remains high for several milliseconds. During the same period the electron temperature shows no increase compared to the pre-ELM values. This SOL dynamics has been observed for a wide range of plasma parameters and is independent of plasma pedestal collisionality. For the first time on JET the convective and conductive ELM energy losses have been quantified using the new kinetic profile measurements. The findings provide detailed confirmation of earlier observations based on different measurements and analysis. The pedestal region perturbed by the ELM is the same for both density and temperature and the ELM effect extends up to about 20% of minor radius. The convective energy losses do not vary significantly and are ~5% of the pedestal stored energy (Wped) over a large range of pedestal collisionality νe* from below νe* = 0.1 to above ve* = 0.5 whereas the conductive losses strongly decrease from ~20% of Wped to 5% of Wped with increasing ve*. The experimental observations are compared to a simple model based on losses being driven by parallel transport.