AbstractIn addition to the Greenwald density limit and the threshold conditions for H-mode access, neoclassical tearing modes (NTMs) pose the most severe constraint to tokamak operation in discharges with conventional (monotonic) current density profiles. We show, at hand of the example of ASDEX Upgrade the resulting constraints on density and useful heating power. At high densities, collisionality effects can lead to the appearance of a second stable regime for NTMs. A further limitation can arise from the appearance of fishbone instabilities which, depending on the orientation of the injected beams, can also lead to a clamping of the total plasma energy content. The resulting diagram is also useful as a guide for a strategy to expand the operating range by feedback stabilisation of the neoclassical tearing modes and for the orientation of the beamlines.