Validation of gyrokinetic modelling of light impurity transport including rotation in ASDEX Upgrade

TL;DR

This study validates gyrokinetic models of impurity transport in tokamaks by comparing simulations with measurements, highlighting the importance of rotation effects and symmetry-breaking mechanisms for accurate impurity profile predictions.

Contribution

It demonstrates the necessity of including rotation-driven effects in gyrokinetic simulations to accurately reproduce impurity profiles in tokamak plasmas.

Findings

Measured boron profiles strongly anti-correlate with rotation gradient.

Nonlinear simulations confirm quasilinear results when including flow shear.

Rotation effects and symmetry-breaking mechanisms are crucial for accurate modeling.

Abstract

Upgraded spectroscopic hardware and an improved impurity concentration calculation allow accurate determination of boron density in the ASDEX Upgrade tokamak. A database of boron measurements is compared to quasilinear and nonlinear gyrokinetic simulations including Coriolis and centrifugal rotational effects over a range of H-mode plasma regimes. The peaking of the measured boron profiles shows a strong anti-correlation with the plasma rotation gradient, via a relationship explained and reproduced by the theory. It is demonstrated that the rotodiffusive impurity flux driven by the rotation gradient is required for the modelling to reproduce the hollow boron profiles at higher rotation gradients. The nonlinear simulations validate the quasilinear approach, and, with the addition of perpendicular flow shear, demonstrate that each symmetry breaking mechanism that causes momentum transport also couples to rotodiffusion. At lower rotation gradients, the parallel compressive convection is required to match the most peaked boron profiles. The sensitivities of both datasets to possible errors is investigated, and quantitative agreement is found within the estimated uncertainties. The approach used can be considered a template for mitigating uncertainty in quantitative comparisons between simulation and experiment.