SOL and pedestal density profile evolution during DIII-D ELMy and ELM-suppressed H-mode operation

Abstract A fast profile reflectometer has been used to study the detailed characteristics of scrape-off-layer (SOL) and pedestal density profile evolution in DIII-D ELMy H-mode plasmas with high temporal (⩾10 μs) and spatial (∼4 mm) resolution. Results show a significant enhancement in radial particle transport to the outer vessel wall during Type-I ELMs. The radial particle transport time (∼140 μs) becomes comparable to the parallel transport time, as a result of a high radial velocity (∼620 m/s) of SOL profile expansion. The dynamics can vary from ELM-to-ELM. Scalings with pedestal density have been obtained, indicating that ELM is less affected as the pedestal density increases. Finally, during ELM-suppressed H-mode operation with a stochastic magnetic boundary, the radial extent of observed SOL profile modifications do not extend to the vessel wall, and profiles are steeper, substantially different from the SOL changes associated with Type-I ELMs.