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H. Meyer, G. Harrer, F. Laggner, EUROfusion MST1 Team et al.:
"Overview of physics studies on ASDEX Upgrade";
Nuclear Fusion, 59 (2019), 11201401 - 11201421.

The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task
force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full
tungsten wall is a key asset for extrapolating to future devices. The high overall heating power,
flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking
the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully noninductive
operation (q95 = 5.5, N 2.8) at low density. Higher installed electron cyclotron
resonance heating power 6 MW, new diagnostics and improved analysis techniques have
further enhanced the capabilities of AUG.
Stable high-density H-modes with Psep/R 11 MW m−1 with fully detached strikepoints
have been demonstrated. The ballooning instability close to the separatrix has been
identified as a potential cause leading to the H-mode density limit and is also found to play an
important role for the access to small edge-localized modes (ELMs). Density limit disruptions
have been successfully avoided using a path-oriented approach to disruption handling and
progress has been made in understanding the dissipation and avoidance of runaway electron
beams. ELM suppression with resonant magnetic perturbations is now routinely achieved
reaching transiently HH98(y,2) 1.1. This gives new insight into the field penetration physics,
in particular with respect to plasma flows. Modelling agrees well with plasma response
measurements and a helically localised ballooning structure observed prior to the ELM is
evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D
perturbations on heat load patterns and fast-ion losses have been further elaborated.
Progress has also been made in understanding the ELM cycle itself. Here, new fast
measurements of Ti and Er allow for inter ELM transport analysis confirming that Er is
dominated by the diamagnetic term even for fast timescales. New analysis techniques allow
detailed comparison of the ELM crash and are in good agreement with nonlinear MHD
modelling. The observation of accelerated ions during the ELM crash can be seen as evidence
for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable
operational regime in DEMO studies of `natural´ no ELM regimes have been extended. Stable
I-modes up to n/nGW 0.7 have been characterised using -feedback.
Core physics has been advanced by more detailed characterisation of the turbulence with
new measurements such as the eddy tilt angle-measured for the first time-or the crossphase
angle of Te and ne fluctuations. These new data put strong constraints on gyro-kinetic
turbulence modelling. In addition, carefully executed studies in different main species (H, D
and He) and with different heating mixes highlight the importance of the collisional energy
exchange for interpreting energy confinement. A new regime with a hollow Te profile now
gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear
interactions of energetic particle modes despite the sub-Alfvénic beam energy. This will help
to validate the fast-ion codes for predicting ITER and DEMO.

nuclear fusion, magnetic confinement, tokamak physics, ITER, DEMO

http://dx.doi.org/10.1088/1741-4326/ab18b8