The JET hybrid H-mode scenario from a pedestal turbulence perspective

TL;DR

This paper characterizes gyrokinetic turbulence in a JET hybrid H-mode pedestal, revealing dominant ITG modes at the pedestal top and ETG modes at the center, with turbulence influenced by shear and impurities.

Contribution

First comprehensive gyrokinetic turbulence analysis of a JET hybrid H-mode pedestal, highlighting the roles of ITG and ETG modes and the effects of shear and impurities.

Findings

Pedestal top transport dominated by ITG modes.

Electron transport driven by ETG modes at the pedestal center.

Strong impact of E×B shear on turbulence levels.

Abstract

Turbulent transport is a decisive factor in determining the pedestal structure of H-modes. Here, we present the first comprehensive characterization of gyrokinetic turbulent transport in a JET hybrid H-mode pedestal. Local, linear simulations are performed to identify instabilities and global, nonlinear electromagnetic simulations reveal the turbulent heat and particle flux structure of the pedestal. Our analysis focuses on the Deuterium reference discharge \#97781 performed in the scenario development for the Deuterium-Tritium campaign. We find the pedestal top transport to be dominated by ion temperature gradient (ITG) modes. In the pedestal center turbulent ion transport is suppressed and electron transport is driven by multi-faceted electron temperature gradient (ETG) modes, which extend down to ion-gyroradius scales. A strong impact of $E\times B$ shear on the absolute turbulence level is confirmed by the global, nonlinear simulations. Furthermore, impurities are shown to reduce the main ion transport. Dedicated density and ion temperature profile variations test the sensitivity of the results and do not find strong differences in the turbulent transport in more reactor-like conditions.