Evolution of a transport limited wide-pedestal structure approaching an ELM

We report on a wide-pedestal H-mode (WPH-mode) regime with periodic ELMs (~ 6 Hz)] where inter-ELM electron pressure pedestal width (△_ped) significantly exceeds (>75%) predictions from the EPED-KBM [Snyder et al, PoP 2009] scaling. This suggests that transport mechanisms other than KBM contribute to the transport in the inter-ELM wide-pedestal phases. This wide-pedestal develops a strikingly different inter-ELM △_ped vs time evolution as compared to the KBM constrained narrow pedestals of type-I ELMy H-mode discharges. The WPH-mode pedestal initially narrows (~10 ms) and then quickly widens (~30 ms) and then saturates before the next ELM. In contrast, the KBM constrained △_ped rapidly increases (few ms) after the ELM and then decreases (~10 ms) to just below its pre-ELM value which is followed by a slow increase up to the next ELM (~14 Hz). The radial profiles of n_e and T_e also confirm the above behaviors in both cases. The △_ped trajectories (narrowing after ELM crash and then widening later) for the WPH-mode tend to support the hypothesis of a transport limited wide-pedestal H-mode (Osborne et al, NF 2015 and Chen et al NF 2017). These results improve our understanding of transport limited pedestals and may inspire new models in low edge ExB shear regimes such as expected in ITER.