Description
Recent studies during the 2025 experimental campaign in ASDEX Upgrade (AUG) have achieved negative triangularity (NT) shaping beyond previous limits. This new set of experiments, guided by the ideal-MHD stability calculations using the BALOO code and supported by predictive results from TCV, have demonstrated a transition to an edge more stable against
peeling ballooning modes, leading to ELM-free plasmas. In some of the AUG cases, a dithery behavior is observed similar to the limit cycle oscillations observed in DIII-D during shaping ramps. In this work we provide the details on the operational boundaries for the NT regime
at various heating mixes and density values. AUG profiles and confinement are compared to a DIII-D discharge similar in shaping and key parameters, although the two machines operate at different values of edge safety factor and have different wall materials. This AUG/DIII-D similarity experiment serves as a basis for comparison of confinement quality and the underlying turbulence regimes using linear and nonlinear gyrokinetic simulations. Achieved ELM avoidance on AUG confirms the universality of the ballooning limited pedestals, previously addressed
on TCV and DIII-D in strongly shaped NT plasmas. Overall, these findings support the feasibility of ELM-free operation in future metal-wall tokamaks using negative-triangularity shaping, offering a viable path forward for high-performance, steady-state fusion scenarios.