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F. Laggner, E. Wolfrum, M. Cavedon, F. Fink, M. Bernert, M. Dunne, P. Schneider, A. Kappatou, G. Birkenmeier, R. Fischer, M. Willensdorfer, F. Aumayr, -. EUROfusion MST1 Team, . ASDEX Upgrade Team:
"Pedestal structure and inter-ELM evolution for different main ion species in ASDEX Upgrade";
Physics of Plasmas, 24 (2017), 5; 0561051 - 0561058.

In tokamak plasmas with different main ion species, a change in confinement occurs, known
as the isotope effect. Experiments comparing hydrogen (H), deuterium (D), and helium (4He)
plasmas have been performed to identify processes that define the pedestal structure and
evolution in between the crashes of edge localized modes (ELMs). The pedestal top electron
densities and temperatures have been matched to compare the pedestal shape and stability. In the
D and H discharges, the pedestal electron temperature profiles do not differ, whereas the density
profile in H has shallower gradients. Furthermore, the heat flux across the pedestal in H is
roughly a factor of two higher than in D. In 4He plasmas at similar stored energy, the pedestal top
electron density is roughly a factor of 1.5 larger than in the references owing to the larger
effective charge. The peeling-ballooning theory, which is independent of the main ion species
mass, can sufficiently describe the pedestal stability in the hydrogenic plasmas. The inter-ELM
pedestal evolution has the same sequence of recovery phases for all investigated species, giving
evidence that similar mechanisms are acting in the pedestals. This is further supported by a similar
evolution of the inter-ELM magnetic signature and the corresponding toroidal structure.