We apply the global gyrokinetic code GENE-3D to perform kinetic-ballooning-mode (KBM) turbulence simulations in the Wendelstein 7-X (W7-X) stellarator using experimentally relevant parameters. In contrast to the flux-tube approach, we observe saturation of the turbulent fluctuations at finite amplitude. Analyzing the turbulent characteristics, we identify the presence of weakly driven KBM turbulence hybridizing with ion-temperature-gradient and trapped-electron-mode turbulence in the scenario under consideration, showing that it is possible that KBM activity can be driven in W7-X, opening up the path for studying this type of turbulence, which is highly relevant for future fusion power plants. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).

We present the first nonlinear, gyrokinetic, radially global simulation of a discharge of the Wendelstein 7-X-like stellarator (W7-X), including kinetic electrons, an equilibrium radial electric field, as well as electromagnetic and collisional effects. By comparison against flux-tube and full-flux-surface simulations, we assess the impact of the equilibrium ExB-flow and flow shear on the stabilisation of turbulence. In contrast to the existing literature, we further provide substantial evidence for the turbulent electron heat flux being driven by trapped-electron-mode (TEM) and electron-temperature-gradient (ETG) turbulence in the core of the plasma. The former manifests as a hybrid together with ion-temperature-gradient (ITG) turbulence and is primarily driven by the finite electron temperature gradient, which has largely been neglected in nonlinear stellarator simulations presented in the existing literature.

The study of the emission properties of the 140 GHz corrugated horn antenna in the frequency range 170–174 GHz has been presented and discussed. This extended frequency range is a part of upgrade of the collective Thomson scattering (CTS) diagnostic at Wendelstein 7-X stellarator. The antenna characterization was done using the raster scan method and thermographic measurements with the help of 175 GHz Clinotron oscillator. The experimental results showed the possibility of the antenna application for the new CTS detector in the both frequency ranges at 140 GHz and 174 GHz.

The W7-X stellarator is optimized with respect to neoclassical transport.Therefore turbulent transport plays an important role.It is equipped with an inertial cooled graphite divertor which intersects the island chain at the plasma edge depending on the magnetic configuration.Additional control coils and the plasma current modify the iota profile at the plasma edge and shift the position of the island chain.To monitor the effects on the poloidal propagation velocity in the scrape-off layer (SOL) and the plasma edge,an O-mode Poloidal Correlation Reflectometer (PCR) is used which simultaneously monitors the propagation of low-k turbulence.Operating in the density range of 0.6 × 1019 m-3 to 2 × 1019 m-3 it covers a large part of the SOL and the plasma edge and allows for the experimental determination in the last closed flux surface (LCFS) and the associated shear layer in low to middensity discharges.In this paper it is shown that the propagation in the shear layer and its vicinity is determined best,when based on an elliptical model.Different magnetic configurations with magnetic edge topology of five independent islands for ι =1 and six linked islands for ι =0.81 are investigated.Also the effects of the plasma current and additional control coils on the edge magnetic topology are studied.The coherence spectra of antenna pairs for different poloidal separations is investigated.Using a decomposition method for the measured coherence spectra the characterization of turbulence spectra is possible with respect to e.g.broad band turbulence and quasi coherent modes.A strong reduction of the broad band turbulence is observed in the vicinity of the LCFS which is evidence for the suppression of low-k turbulence at the shear layer.

Experimental investigations of the evolution of the dynamics of drift wave turbulence in a linear high-density helicon plasma device are presented. The turbulent density fluctuations in the plasma edge are characterized by large intermittent events caused by radially propagating turbulent structures, which are formed in the radial plasma density region due to increased cross-field transport by a quasi-coherent drift wave mode. Similar to coherent drift wave modes the turbulent structures are correlated with fluctuating parallel currents. The role of fluctuating currents parallel to the ambient magnetic field in the evolution of coherent drift wave modes and drift turbulence is highlighted by investigations of the interaction of drift wave fluctuations with externally driven currents. Frequency pulling of coherent drift wave modes over a frequency range of up to 30% of the natural drift wave frequency is demonstrated. Furthermore, the drive of mode-selective current patterns allow for complete synchronization of drift wave turbulence and consequently leads to a strong reduction of the associated fluctuation-induced transport.

Emissive probes are standard tools in laboratory plasmas for the direct determination of the plasma potential. Usually they consist of a loop of refractory wire heated by an electric current until sufficient electron emission. We have developed and investigated various types of emissive probes which were heated by a focused infrared laser beam. Such a probe has several advantages: higher probe temperature without evaporation or melting and thus higher emissivity and longer lifetime, no deformation of the probe in a magnetic field, no potential drop along the probe wire, faster time response. The probes are heated by an infrared diode laser with 808 nm wavelength and an output power up to 50 W.

Emissive probes are standard tools in laboratory plasmas for the direct determination of the plasma potential. Usually they consist of a loop of refractory wire heated by an electric current until sufficient electron emission. Recently emissive probes were used also for measuring the radial fluctuation-induced particle flux and other essential parameters of edge turbulence in magnetized toroidal hot plasmas [R. Schrittwieser et al., Plasma Phys. Controlled Fusion 50, 055004 (2008)]. We have developed and investigated various types of emissive probes, which were heated by a focused infrared laser beam. Such a probe has several advantages: higher probe temperature without evaporation or melting and thus higher emissivity and longer lifetime, no deformation of the probe in a magnetic field, no potential drop along the probe wire, and faster time response. The probes are heated by an infrared diode laser with 808 nm wavelength and an output power up to 50 W. One probe was mounted together with the lens system on a radially movable probe shaft, and radial profiles of the plasma potential and of its oscillations were measured in a linear helicon discharge.