Understanding the core density profile in TCV H-mode plasmas

TL;DR

This study analyzes how turbulence and collisionality influence electron density profiles in TCV H-mode plasmas, revealing that turbulence regimes and the Ware-pinch significantly affect density peaking, with simulations aligning qualitatively with experiments.

Contribution

It demonstrates that turbulence regimes, rather than collisionality alone, primarily determine the core density profile in TCV H-mode plasmas, supported by both experimental analysis and gyrokinetic simulations.

Findings

Electron density gradient increases with collisionality in certain regimes.

Turbulence regime, influenced by electron and ion temperature ratios, governs density peaking.

Ware-pinch can significantly enhance density peaking in ohmic plasmas.

Abstract

Results from a database analysis of H-mode electron density profiles on the Tokamak \`a Configuration Variable (TCV) in stationary conditions show that the logarithmic electron density gradient increases with collisionality. By contrast, usual observations of H-modes showed that the electron density profiles tend to flatten with increasing collisionality. In this work it is reinforced that the role of collisionality alone, depending on the parameter regime, can be rather weak and in these, dominantly electron heated TCV cases, the electron density gradient is tailored by the underlying turbulence regime, which is mostly determined by the ratio of the electron to ion temperature and that of their gradients. Additionally, mostly in ohmic plasmas, the Ware-pinch can significantly contribute to the density peaking. Qualitative agreement between the predicted density peaking by quasi-linear gyrokinetic simulations and the experimental results is found. Quantitative comparison would necessitate ion temperature measurements, which are lacking in the considered experimental dataset. However, the simulation results show that it is the combination of several effects that influences the density peaking in TCV H-mode plasmas.