Heat transport and core turbulence measurements on the optimized stellarator Wendelstein 7-X

The optimized stellarator Wendelstein 7-X (W7-X) is designed to have an approximately quasi-isodynamic (QI) magnetic configuration with reduced neoclassical transport compared to a classical stellarator, and turbulent transport is expected to be a significant source of heat transport across the plasma minor radius. The Ion Temperature Gradient (ITG) and Trapped Electron Mode (TEM) are the dominant turbulence channels in low beta W7-X plasmas, and gyrokinetic modelling indicates two major differences between ITG/TEMs in W7-X and previous tokamak and stellarator experiments. The ITG mode is predicted to be highly localized along a helical band in W7-X, causing a reduction of the associated turbulence, and the nearly QI configuration of W7-X is predicted to be resilient to collisionless TEMs. In this contribution, the electron heat transport is compared to neoclassical predictions, and the stiffness in the electron heat transport is compared to TEM/ITG mode driven turbulence in two magnetic configurations of W7-X: one nearly QI configuration as well as a configuration with deliberately reduced QI. Additionally, electron temperature and plasma density fluctuations are compared to linear and nonlinear gyrokinetic calculations to assess the stabilization of TEM turbulence in W7-X.