A. von Stechow
A5053303516- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Laser-Plasma Interactions and Diagnostics
- Plasma Diagnostics and Applications
- Fusion materials and technologies
- Superconducting Materials and Applications
- Particle accelerators and beam dynamics
- Fluid Dynamics and Turbulent Flows
- Atomic and Subatomic Physics Research
- Laser-induced spectroscopy and plasma
- Magnetic Field Sensors Techniques
- Advanced MRI Techniques and Applications
- Nuclear reactor physics and engineering
- Adaptive optics and wavefront sensing
- Magnetic properties of thin films
- Laser Design and Applications
- Geomagnetism and Paleomagnetism Studies
- Electromagnetic Launch and Propulsion Technology
- Atomic and Molecular Physics
- Nuclear Physics and Applications
- Stellar, planetary, and galactic studies
- X-ray Spectroscopy and Fluorescence Analysis
- Magnetic Properties of Alloys
- Astronomical Observations and Instrumentation
Max Planck Institute for Plasma Physics
2014-2025
Max Planck Institute for Plasma Physics - Greifswald
2015-2024
Max Planck Society
2012-2021
Princeton Plasma Physics Laboratory
2021
HUN-REN Centre for Energy Research
2021
Abstract The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor and plasma volume) restarted operation after the assembly of a graphite heat shield 10 inertially cooled island divertor modules. This paper reports on results from first high-performance operation. Glow discharge conditioning ECRH discharges in helium turned out to be important for density edge radiation control. Plasma densities with central electron temperatures were routinely achieved...
Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future power plant. Plasma operation started in 2015 using limiter configuration. After installing an uncooled magnetic island divertor, extending energy limit from 4 80 MJ, continued 2017. For this phase, electron cyclotron resonance heating (ECRH) capability was extended 7 MW, and hydrogen pellet injection implemented. The enhancements resulted highest triple...
A significant improvement of plasma parameters in the optimized stellarator W7-X is found after injections frozen hydrogen pellets. The ion temperature post-pellet phase exceeds 3 keV with 5 MW electron heating and global energy confinement time surpasses empirical ISS04-scaling. realized such experiments are significantly above those comparable gas-fuelled discharges. In this paper, we present details these pellet discuss main properties during enhanced phases. Local power balance applied...
The neoclassical transport optimization of the Wendelstein 7-X stellarator has not resulted in predicted high energy confinement gas fueled electron-cyclotron-resonance-heated (ECRH) plasmas as modelled (Turkin et al 2011 Phys. Plasmas 18 022505) due to levels turbulent heat observed experiments. electron-turbulent-heat appears non-stiff and is electron temperature gradient (ETG)/ion (ITG) type (Weir 2021 Nucl. Fusion 61 056001). As a result, Te can be varied freely from 1 keV–10 keV within...
Abstract We demonstrate favorable stability properties of maximum- J stellarators, exemplified by the Wendelstein 7-X (W7-X) device, in scenarios with low plasma beta. A large number electrostatic linear gyrokinetic simulations are conducted to scan relevant parameter space for different configurations, resulting maps that account key micro-instabilities thought drive turbulent transport. These exhibit a ‘stability valley’ region where normalized ion temperature gradient is roughly equal...
Pulsed injections of boron carbide granules into Wendelstein 7-X stellarator (W7-X) plasmas transiently increase the plasma stored energy and core ion temperatures above reference W7-X experimental programs by up to 30%. In a series 4 MW electron cyclotron resonance heating experiments, PPPL Probe Mounted Powder Injector provided 50 ms bursts 100 μm every 350 at estimated quantities ranging from approximately 1 mg/pulse over 30 mg/pulse. For each injection, was observed initially drop...
We report detailed laboratory observations of the structure a reconnection current sheet in two-fluid plasma regime with guide magnetic field. observe and quantitatively analyze quadrupolar electron pressure variation ion-diffusion region, as originally predicted by extended magnetohydrodynamics simulations. The projection gradient parallel to field contributes significantly balancing electric field, resulting cross-field jets layer are diamagnetic origin. These results demonstrate how...
Abstract During the two most recent experimental campaigns in advanced stellarator Wendelstein 7-X (W7-X) (Klinger et al 2017 Plasma Phys. Control. Fusion 59 014018; Bosch Nucl. 57 116015; Wolf 102020; Pedersen Plasmas 24 0555030) hydrogen ice pellet injection was performed for first time. In order to investigate potential of fueling W7-X and study particle deposition a large stellarator, blower-gun system installed with 40 pellets capability. The experience gained this will be used...
Abstract A series of ice pellets was injected into the advanced stellarator Wendelstein 7-X (W7-X). Although were small and slow, deep efficient particle fueling could be observed experimentally. The most striking feature appearing after injection pellets, however, a transient increase in energy confinement time. This phase resembled several aspects modes enhanced gas-puff or pellet injection, as other fusion experiments. All experimental attempts, to prolong this phase, failed. In paper,...
A system for studying the spatiotemporal dynamics of fluctuations in boundary W7-X plasma using “Gas-Puff Imaging” (GPI) technique has been designed, constructed, installed, and operated. This GPI addresses a number challenges specific to long-pulse superconducting devices, such as W7-X, including long distance between vacuum vessel wall, diagnostic ports, range last closed flux surface (LCFS) locations different magnetic configurations management heat loads on system’s plasma-facing...
Abstract We study the effect of turbulent transport in different magnetic configurations Weldenstein 7-X stellarator. In particular, we performed direct numerical simulations with global gyrokinetic code GENE-3D, modeling behavior Ion Temperature Gradient turbulence Standard, High-Mirror and Low-Mirror W7-X. found that configuration produces more than both Standard configurations. By comparison radially local simulations, have demonstrated importance performing non-linear to predict fluxes...
In this Letter, we demonstrate by comparison of computer simulations and experimental results that excitation turbulence-driven electromagnetic secondary instabilities can serve as a paradigm to explain the observed activity otherwise stable modes in fusion devices. particular, discuss Alfvén eigenmodes electron cyclotron heated plasmas Wendelstein 7-X (W7-X) stellarator. more than 700 programs W7-X Operational Phase 1.2b (from which 25 were selected discussed paper), poloidal magnetic...
Abstract In the island divertor scrape-off layer (SOL) of Wendelstein 7-X stellarator, 2D-resolved Langmuir probe measurements uncover a complex spatial structure electron temperature, density, and floating potential. Depending on details magnetic size position, significant poloidal gradients non-monotonic radial profiles are observed. The resulting electric fields imply presence sheared stationary drift flows with velocities few km/s, flow channels as narrow one cm. Such observed gas puff...
A linear experiment dedicated to the study of driven magnetic reconnection is presented. The new device (VINETA II) suitable for investigating both collisional and near collisionless reconnection. Reconnection achieved by externally driving field lines towards an X-point, inducing a current in background plasma which consequently modifies topology. Owing open line configuration experiment, limited axial sheath boundary conditions. gun used as additional electron source order counterbalance...
Abstract In electron (cyclotron) heated plasmas, in both ASDEX Upgrade ( L -mode) and Wendelstein 7-X, clamping of the ion temperature occurs at T i ∼ 1.5 keV independent magnetic configuration. The ions such plasmas are through energy exchange power as <?CDATA ${n}_{\mathrm{e}}^{2}({T}_{\mathrm{e}}-{T}_{\mathrm{i}})/{T}_{\mathrm{e}}^{3/2}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow>...
A phase contrast imaging (PCI) diagnostic has been developed for the Wendelstein 7-X (W7-X) stellarator. This diagnostic, funded by U.S. Department of Energy through Office Fusion Sciences, is a collaboration between Max Planck Institute Plasmaphysics, MIT, and SUNY Cortland. The primary motivation development PCI measurement turbulent fluctuations, such as ion temperature gradient, electron trapped mode instabilities. Understanding how magnetic geometry other externally controllable...
The role of the radial electric field in high-performance ion-root plasmas on Wendelstein 7-X (W7-X) is examined and compared with neoclassical predictions. W7-X stellarator world's first large-scale optimized stellarator. One important targets chosen for optimization during design process was reduction core heat transport. This targeted reactor-relevant high-density which ambipolar expected to be negative throughout core.
First experimental observations in the Wendelstein 7-X stellarator indicate that impurity confinement can be explained by turbulent processes. In particular, plasma discharges with increased ion to electron temperature ratio are accompanied reduced density fluctuation amplitudes and anomalous diffusion, suggesting a lower transport. Employing gyro-kinetic numerical simulations, we argue plays key role for reducing gradient instability 7-X, leading an enhanced confinement.
We assess the magnetic field configuration in modern fusion devices by comparing experiments with same heating power, between a stellarator and heliotron. The key role of turbulence is evident optimized stellarator, while neoclassical processes largely determine transport heliotron device. Gyrokinetic simulations elucidate underlying mechanisms promoting stronger ion scale stellarator. Similar plasma performances these suggests that turbulent should both be next step reactor designs.
The fundamental nature of turbulent density fluctuations in standard Wendelstein 7-X (W7-X) stellarator discharges is investigated experimentally via phase contrast imaging (PCI) combination with gyrokinetic simulations the code GENE. We find that are ion-temperature-gradient-driven and radially localised outer half plasma. It shown line-integrated PCI measurements cover right range wavenumbers a favourable toroidal poloidal location to capture some strongest W7-X. Due radial localisation...
The dynamics of magnetic reconnection on temporal and spatial scales ranging from the global boundary conditions down to microscopic are experimentally investigated in linear, guide-field experiment Vineta.II. On scale, current driven by varying fields is well described an inductive electrical circuit, limiting rate external geometry path. A sheet forms that has a three-dimensional structure due X-point topology together with non-equilibrium pressure lead both distortion expansion along...
A phase contrast imaging (PCI) diagnostic has been developed for the Wendelstein 7-X (W7-X) stellarator. The PCI provides a line-integrated measurement of turbulent electron density fluctuations, which is essential understanding high performance scenarios that can lead to improved confinement at fusion-relevant temperatures and densities. system also sensitive coherent arise from Alfvén eigenmodes or other MHD activity. This paper an overview hardware optical presents example W7-X OP1.2b...
Abstract At the W7-X stellarator, bolometer system has measured an intensive radiation zone in inner plasma region (at a normalized radius ρ ∼ 0.3–0.4) hydrogen generated by electron cyclotron resonance heating; it differs from normal distribution with edge-localized emission zone. Spectroscopic diagnostics have recorded high-Z elements such as iron. This phenomenon happens phases after gas supply turn-off, which results all impurity relevant diagnostic signals increasing for several...