Impact of ICRF fast-ions on core turbulence and MHD activity in ASDEX upgrade

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The successful operation of fusion reactors requires operatingscenarios with good core confinement and acceptable first wall heat loads, thatare stable and robust to external perturbations. This poses both physical andtechnological challenges. One of the technologies addressing these challengesis a complex feedback control system. They support advances in physicalunderstanding and help to ensure stable operating conditions. Operatingmarginally stable plasmas often leads to off-normal events (such as disruptions)and feedback control can prevent these to some extent.This contribution gives an overview of the main results of the developmentand operation of the feedback control algorithms on ASDEX Upgrade (AUG).Fueling actuators, using a combination of gas valves and pellet injection, cansimultaneously control neutral density of the divertor and the density of theplasma core above the Greenwald limit. Impurity injection is employed to controlthe position of the X-point radiator, allowing the creation of an ELM-suppressedH-mode with high radiation fraction. Heating actuators are used to controlthe plasma energy content, which supports advanced tokamak experiments andenables stable I-mode operation, and the electron temperature control, whichsupports turbulence studies. In control technology, AUG has pioneered the useof virtual actuators, which allow effective use of the limited number of heatingactuators, adaptive control policies, and exception handling. Such technologieswill also be used in ITER. Advanced nonlinear state observers (RAPTOR,RAPDENS) and codes to evaluate the power deposition properties (RABBIT,TORBEAM) are available for routine use in the AUG feedback controllers.Extensive use of the AUG Discharge Control System (DCS) further enhancesthe research capabilities of this machine.

Section: Heating Controlmentioning

confidence: 99%

Overview of advances in ASDEX Upgrade plasma control to support critical physics research for ITER and beyond

Kudlacek,

David,

Gomez

et al. 2024

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Full-radius integrated modelling of ASDEX Upgrade L-modes including impurity transport and radiation

Fajardo,

Angioni,

Dux

et al. 2024

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An integrated framework that demonstrates multi-species, multi-channel modelling capabilities for the prediction of impurity density profiles and their feedback on the main plasma through radiative cooling and fuel dilution is presented. It combines all presently known theoretical elements in the local description of quasilinear turbulent and neoclassical impurity transport, using the models TGLF-SAT2 and FACIT. These are coupled to the STRAHL code for impurity sources and radiation inside the ASTRA transport solver. The workflow is shown to reproduce experimental results in full-radius L-mode modelling. In particular, a set of ASDEX Upgrade L-modes with differing heating power mixtures and plasma currents are simulated, including boron (B) and tungsten (W) as intrinsic impurities. The increase of predicted confinement with higher current and the reduction of core W peaking with higher central wave heating are demonstrated. Furthermore, a highly radiative L-mode scenario featuring an X-point radiator (XPR) with two intrinsic (B, W) and one seeded argon (Ar) species is simulated, and its measured radiated power and high confinement are recovered by the modelling. The stabilizing effect of impurities on turbulence is analyzed and a simple model for the peripheral X-point radiation is introduced. A preliminary full-radius simulation of an H-mode phase of this same discharge, leveraging recent work on the role of the E×B shearing at the edge, shows promising results.

Impact of supra-thermal particles on plasma performance at ASDEX Upgrade with GENE-Tango simulations

Di Siena,

Bilato,

Bañón Navarro

et al. 2024

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This paper presents global gyrokinetic simulations on the transport time scale of an ASDEX Upgrade H-mode discharge showing a pronounced peaking of the on-axis ion temperature profiles. Leveraging the newly developed GENE-Tango tool, which combines the global gyrokinetic code GENE with the transport solver Tango, we investigate the impact of energetic particles and electromagnetic effects on the improved plasma performance observed in the experimental discharge. Our results reveal that a striking agreement between the GENE-Tango simulations and the experimental measurements can be achieved only when energetic particles and electromagnetic effects are simultaneously retained in the modeling. In contrast, when these are neglected we observed a significant underestimation of the on-axis ion temperature, aligning with profiles computed using TGLF-ASTRA. The peaking in the ion temperature profile observed in the simulations can be attributed to the effective suppression of turbulence by high-frequency electromagnetic modes, likely Kinetic Ballooning Modes (KBM) / Alfv\'en eigenmodes (AEs). These modes play a critical role in enhancing zonal flow activity and shearing rate levels which thus lead to a localized increase in the temperature gradient. However, it is crucial to maintain these modes at a state of marginal stability or weak instability to prevent energetic particle turbulence destabilization. Otherwise, the result would be a flattening of all the thermal profiles. Interestingly, we found that global GENE-Tango simulations are required to model correctly the linear dynamics of these high-frequency modes. Additionally, global simulations demonstrate greater tolerance than flux-tube simulations for marginal instability of these high frequency modes while maintaining power balance agreement. 