Stellarators have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of optimised stellarators like Wendelstein 7-X (W7-X), in which the collisional transport is reduced by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. With W7-X, a well-diagnosed advanced stellarator, we can directly probe turbulence in the flexible magnetic geometry and compare against state-of-the-art gyrokinetic codes. After giving a brief introduction to stellarators and an overview over W7-X, recent findings on electrostatic and electromagnetic turbulence in W7-X will be shown, e.g. how, at much lower normalised plasma pressure than previously anticipated, kinetic ballooning modes that appear below the MHD threshold can lead to an increase in ITG-driven turbulent transport [1,2] or that heat-pulse propagation experiments confirm rather benign transport caused by electron-temperature gradient modes [3]. We will also discuss whether the density-gradient-driven trapped-electron mode (TEM) is indeed more benign in W7-X as predicted by theory [4], and whether an up to now not conclusively identified mode - possibly its sibling, the electron-temperature-gradient-driven TEM - might be the cause of a sudden change in particle and heat diffusivity observed at high plasma density [5].

[1]   P. Mulholland, K. Aleynikova, B. J. Faber, M. J. Pueschel, J. H. E. Proll, C. C. Hegna, P. W. Terry, and C. Nührenberg, Phys. Rev. Lett. 131, 185101 (2023).
[2]   P. Mulholland, A. Zocco, M. C. L. Morren, K. Aleynikova, M. J. Pueschel, J. H. E. Proll, and P. W. Terry, J. Plasma Phys. 91 (2025).
[3]   G. G. Plunk, P. Xanthopoulos, G. M. Weir, S. A. Bozhenkov, A. Dinklage, G. Fuchert, J. Geiger, M. Hirsch, U. Hoefel, M. Jakubowski, A. Langenberg, N. Pablant, E. Pasch, T. Stange, and D. Zhang, Phys. Rev. Lett. 122, 035002 (2019).
[4]   J. H. E. Proll, P. Helander, J. W. Connor, G. G. Plunk, and G. G. Plunk, Phys. Rev. Lett. 108, 245002 (2012).
[5]   S. Bannmann, O. Ford, P. Zs. Poloskei, J. Svensson, A. Pavone, S. Kwak, U. Hoefel, E. Pasch, G. Fuchert, H. M. Smith, S. Lazerson, P. McNeely, N. Rust, D. Hartmann, R. C. Wolf, and the W.-X. Team, Nucl. Fusion 64, 106015 (2024).