Experiments and numerical modelling of negative triangularity ASDEX Upgrade plasmas in view of DTT scenarios

This contribution presents experimental and modelling results of a comparison of negative (NT) and positive (PT) triangularity ASDEX Upgrade (AUG) discharges using the plasma shapes presently foreseen in the DTT tokamak, under construction in Frascati, Italy [1]. This work is part of a broader framework of investigation aiming at understanding whether the good properties observed in NT scenarios in devices like DIII-D and TCV will extrapolate to the DTT device and more in general to DEMO and fusion reactors. Unlike in DIII-D and TCV, NT discharges in AUG tend to go into H-mode when operated in the common favourable ion ?B drift configuration. Therefore, for the comparison both favourable and unfavourable configurations have been used [2]. The aim of the comparison with a PT H-mode has been to check whether the loss of the PT high pedestal is recovered in NT L-modes (or NT low pedestal H-modes) within a broader edge region, leading to similar core region kinetic parameters (hence fusion power in DT devices). This does not generally imply similar global confinement, given the weight of the edge volume in global parameters. Discharges with mixed NBI and ECR heating and with pure ECR heating have been compared, to study the effect of varying the ITG vs TEM relative weight, although ITG is the dominant mode in most cases. For plasmas heated with NBI and ECR auxiliary power, the experimental results have shown that the NT geometry does not allow to recover the core performance of a PT H-mode. Instead, NT discharges with pure ECRH present logarithmic pressure gradients in the region 0.7<?tor<1 high enough to recover the PT thermal pressure. Predictive simulations of both PT and NT plasmas have been performed with the aim of investigating their transport properties. The simulations have been carried out using the transport code ASTRA [3] and turbulent transport model TGLF-SAT2 [4]. The transport of the main species is modelled up to the top of the pedestal in H-modes and up to the separatrix in L-modes. The impurities are predicted selfconsistently up to the separatrix radius in all cases. Rotation is taken from experiment data, but not predicted. Results for both heating regimes are presented. In general, the integrated modelling reproduces well the discharges both in PT and NT configurations, including the reduced transport in NT ECH only cases. The physics understanding of the different behaviour of the NBI+ECR vs ECR plasmas is in progress, also with the help of gyrokinetic simulations.