Electron-temperature-gradient-driven ion-scale turbulence in high-performance scenarios in Wendelstein 7-X

Through intercode gyrokinetic numerical simulations, we predict that, for the conditions met during improved performances in the stellarator Wendelstein 7-X, turbulent transport can be dominated by electron-temperature-gradient-driven ion-scale electrostatic turbulence. We find that previously numerically observed large density-gradient-driven turbulence reductions must be attributed to the artificial suppression of the electron temperature gradient. Instead, when electrons have a finite temperature gradient, we observe a moderate turbulence suppression whose quantitative comparison with experimental findings remains challenging. In such partial suppression, the nonlinear dynamics of zonal flows plays a pivotal role as opposed to the underlying most unstable linear modes.