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View article: Stable Small Plasmas at the Density Limit in the W7-X Stellarator
Stable Small Plasmas at the Density Limit in the W7-X Stellarator Open
Experiments in the Wendelstein 7-X (W7-X) stellarator with plasma density beyond the established density limit in stellarators [Scalings of energy confinement and density limit in stellarator/heliotron devices, .] resulted in unusual, redu…
View article: Magnetic geometry effects on turbulent density fluctuations in Wendelstein 7-X
Magnetic geometry effects on turbulent density fluctuations in Wendelstein 7-X Open
Line-integrated density fluctuation measurements from the core of the optimised stellarator Wendelstein 7-X (W7-X) are studied in the context of magnetic field geometry changes. The amplitude as well as the spectral distribution of fluctua…
View article: In-situ calibration of charge exchange spectroscopy for spatially resolved measurements of helium-hydrogen density ratio in Wendelstein 7-X
In-situ calibration of charge exchange spectroscopy for spatially resolved measurements of helium-hydrogen density ratio in Wendelstein 7-X Open
In-situ calibration of charge exchange spectroscopy for spatially resolved measurements of helium-hydrogen density ratio is described in this paper. The helium-hydrogen density ratio in the core plasma is derived from the intensity ratio o…
View article: The suppression of anomalous impurity transport above a critical normalized density gradient scale length in Wendelstein 7-X
The suppression of anomalous impurity transport above a critical normalized density gradient scale length in Wendelstein 7-X Open
In purely neutral-beam-heated scenarios in Wendelstein 7-X (W7-X), central peaking of impurity density profiles is observed. These are discharges typically considered as the main path towards high energy confinement in W7-X. Understanding …
View article: Measurements of radial neutral density profiles from Balmer-<i>α</i> emission in Wendelstein 7-X
Measurements of radial neutral density profiles from Balmer-<i>α</i> emission in Wendelstein 7-X Open
Radial neutral density profiles are estimated from measurements of passive H α emission in the Wendelstein 7-X stellarator. To parametrize the generally three-dimensional distribution with a low number of degrees of freedom, the neutral de…
View article: First motional stark effect measurements at Wendelstein 7-X
First motional stark effect measurements at Wendelstein 7-X Open
The rotational transform plays a crucial role in magnetic confinement devices and its profile is directly related to stability and confinement properties. A popular way to assess the rotational transform profile is using a Motional Stark E…
View article: Visible core spectroscopy at <b>Wendelstein 7-X</b>
Visible core spectroscopy at <b>Wendelstein 7-X</b> Open
This paper presents an overview of recent hardware extensions and data analysis developments to the Wendelstein 7-X visible core spectroscopy systems. These include upgrades to prepare the in-vessel components for long-pulse operation, nin…
View article: Validation of a synthetic fast ion loss detector model for Wendelstein 7-X
Validation of a synthetic fast ion loss detector model for Wendelstein 7-X Open
We present the first validated synthetic diagnostic for fast ion loss detectors (FILDs) in the Wendelstein 7-X (W7-X) stellarator. This model has been developed on, and validated against experimental data from, a FILD provided by the Natio…
View article: Turbulence-reduced high-performance scenarios in Wendelstein 7-X
Turbulence-reduced high-performance scenarios in Wendelstein 7-X Open
In the Wendelstein 7-X (W7-X) stellarator, turbulence is the dominant transport mechanism in most discharges. This leads to a ‘clamping’ of ion temperature over a wide range of heating power, predominantly flat density profiles where hollo…
View article: Impurity transport study based on measurement of visible wavelength high-n charge exchange transitions at W7-X
Impurity transport study based on measurement of visible wavelength high-n charge exchange transitions at W7-X Open
A recently installed high-speed charge exchange diagnostic at the W7-X stellarator has been used to identify several high-n Rydberg emission lines near 500 nm following impurity injections. The wavelengths of observed high-n Rydberg transi…
View article: First measurements with a Coherence Imaging Charge Exchange Recombination Spectroscopy (CICERS) diagnostic at Wendelstein 7-X
First measurements with a Coherence Imaging Charge Exchange Recombination Spectroscopy (CICERS) diagnostic at Wendelstein 7-X Open
In this work, the Coherence Imaging Spectroscopy technique is exploited for active charge exchange radiation measurements to infer high spatial resolution 2D ion temperature ( ) maps in the core region of Wendelstein 7-X plasmas. A sy…
View article: Evaluation and validation of radial impurity density profiles from CXRS using neutral beam modelling in W7-X
Evaluation and validation of radial impurity density profiles from CXRS using neutral beam modelling in W7-X Open
Absolute radial impurity density profiles in the Wendelstein 7-X stellarator (W7-X) are derived from charge exchange recombination spectroscopy using modelling of the neutral beam. The approach is validated via cross comparisons of the neu…
View article: Suppression of anomalous impurity transport in NBI-heated W7-X plasmas
Suppression of anomalous impurity transport in NBI-heated W7-X plasmas Open
Radial impurity density profiles in two Wendelstein 7-X (W7-X) experiments heated by neutral beam injection (NBI) are analyzed with respect to their impurity transport properties. Local impurity densities are derived from charge exchange r…
View article: Effect of spatial distribution of impurity ions on the signal of ‘C/O monitor for Wendelstein 7-X’ - an indicator of plasma wall interactions
Effect of spatial distribution of impurity ions on the signal of ‘C/O monitor for Wendelstein 7-X’ - an indicator of plasma wall interactions Open
View article: Ion temperature clamping in Wendelstein 7-X electron cyclotron heated plasmas
Ion temperature clamping in Wendelstein 7-X electron cyclotron heated plasmas Open
The neoclassical transport optimization of the Wendelstein 7-X stellarator has not resulted in the predicted high energy confinement of gas fueled electron-cyclotron-resonance-heated (ECRH) plasmas as modelled in (Turkin et al 2011 Phys. P…
View article: Analysis of influences of pressure anisotropies on the 3D MHD equilibrium in LHD
Analysis of influences of pressure anisotropies on the 3D MHD equilibrium in LHD Open
3D equilibria with an anisotropic pressure component in the large helical device are analyzed with respect to their magnetic axis locations. The anisotropic extension of the 3D equilibrium solver variational moments equilibrium code, aniso…
View article: EMC3-EIRENE simulation of first wall recycling fluxes in W7-X with relation to H-alpha measurements
EMC3-EIRENE simulation of first wall recycling fluxes in W7-X with relation to H-alpha measurements Open
In the Wendelstein 7-X stellarator, the main locations of particle sources are expected to be the carbon divertors, baffles and graphite heat shield first wall. In this paper, the heat shield is implemented in EMC3-EIRENE to understand the…