The type-I ELM-free EDA and QCE regimes in ASDEX Upgrade - similarities and differences

The enhanced D-alpha (EDA, [Greenwald, PoP, 1999]) and the quasi-continuous exhaust (QCE, [Faitsch, NME, 2021]) regimes are type-I ELM-free regimes. Since the beginning of type-II studies in ASDEX Upgrade - later named QCE - the similarity to the EDA regime of C-MOD was recognised [Stober, NF, 2001]. The EDA without apparent filament activity was identified more recently in ASDEX Upgrade [Gil, NF, 2020].

An extensive diagnostics set-up allows to study the differences and similarities between EDA and QCE. The most striking similarities are (i) the presence of a mode at the pedestal foot, close to the separatrix and called the quasi-coherent mode (QCM) and (ii) the access conditions, favoured by high plasma shaping and sufficient fuelling. The most prominent difference are (i) the strong filamentary activity in the scrape-off layer in the QCE regime compared to their near absence in EDA and (ii) the broadened power fall-off length in QCE [Faitsch, NME, 2021].

This contribution presents the existence space of both EDA and QCE in terms of global as well as local separatrix plasma parameters, with QCE being at higher plasma pressure and higher separatrix density compared to EDA which is operated closer to the L-H power threshold. The conditions at which filaments are visible in the divertor will be discussed.