D. Naujoks
A5068962312- Magnetic confinement fusion research
- Fusion materials and technologies
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Superconducting Materials and Applications
- Plasma Diagnostics and Applications
- Nuclear Materials and Properties
- Ionosphere and magnetosphere dynamics
- Nuclear reactor physics and engineering
- Ion-surface interactions and analysis
- Laser-induced spectroscopy and plasma
- Nuclear Physics and Applications
- Solar and Space Plasma Dynamics
- Atomic and Molecular Physics
- Electron and X-Ray Spectroscopy Techniques
- Metal and Thin Film Mechanics
- Diamond and Carbon-based Materials Research
- Advanced materials and composites
- Risk and Safety Analysis
- Dust and Plasma Wave Phenomena
- Safety Systems Engineering in Autonomy
- X-ray Spectroscopy and Fluorescence Analysis
- Atomic and Subatomic Physics Research
- High-pressure geophysics and materials
- Semiconductor materials and devices
Max Planck Institute for Plasma Physics - Greifswald
2013-2024
Max Planck Institute for Plasma Physics
2009-2021
Max Planck Society
2010-2021
John Wiley & Sons (Germany)
2019
Australian National University
2016
Oak Ridge National Laboratory
2016
Physikalisch-Technische Bundesanstalt
2016
University of Opole
2016
CEA Cadarache
2016
National Institute for Fusion Science
2016
Several experiments were conducted in ASDEX Upgrade to prove the suitability of tungsten as a divertor target material under conditions high density and low temperature divertor. The observed fluxes from tile into plasma are low, keeping with extremely sputtering yields. In addition, very favourable effect `prompt redeposition' (redeposition during first gyration) could be confirmed by experiments. Cooling edge region neon injection seems permissible, i.e. impurity did not increase eroded...
Feedback-controlled puffing of neon and deuterium has been applied to control the edge-localized-mode behavior target plate power deposition during high-power $H$-mode discharges in ASDEX Upgrade. A regime found which more than 90% heating is lost through radiation divertor detachment occurs, without deterioration energy confinement. The plasma remains $H$ mode, exhibiting small-amplitude, high-frequency ELM's, do not penetrate plates strike zone region.
A promising new plasma operational regime on the Wendelstein stellarator W7-AS has been discovered. It is extant above a threshold density and characterized by flat profiles, high energy low impurity confinement times, edge-localized radiation. Impurity accumulation avoided. Quasistationary discharges with line-averaged densities n(e) to 4 x 10(20) m(-3), radiation levels 90%, partial detachment at divertor target plates can be simultaneously realized. Energy up twice that of standard...
Abstract Wendelstein 7-X (W7-X), the largest advanced stellarator, is built to demonstrate high power, performance quasi-continuous operation. Therefore, in recent campaign, experiments were performed prepare for long pulse operation, addressing three critical issues: development of stable detachment, control heat and particle exhaust, impact leading edges on plasma performance. The exhaust W7-X realized with help an island divertor, which utilizes large magnetic islands at boundary. This...
W7-AS has recently been equipped with ten open divertor modules in order to experimentally evaluate the island concept. First results are reported this paper. The new divertors enable access a NBI-heated, very high density (up e = 3.5 × 1020 m-3) operating regime promising confinement properties. energy time increases steeply and then saturates. In contrast, particle impurity times decrease increasing density. This allows full control quasi-steady-state operation also under conditions of...
Wendelstein 7-X, a superconducting optimized stellarator built in Greifswald/Germany, started its first plasmas with the last closed flux surface (LCFS) defined by 5 uncooled graphite limiters December 2015. At end of 10 weeks long experimental campaign (OP1.1) more than 20 independent diagnostic systems were operation, allowing detailed studies many interesting plasma phenomena. For example, fast neutral gas manometers supported video cameras (including one fast-frame camera frame rates...
The completely detached high confinement (CDH) regime established recently in power ASDEX-Upgrade single null divertor discharges is described. standard CDH mode scenario with feedback controlled external deuterium and neon puffing analysed detail respect to its detachment properties. Impurity transport pumping effects the density operation windows of are outlined. First results other impurity radiators (N,Ar) given. Finally space discussed terms main chamber scrape-off layer plus radiation...
The main objective of the Wendelstein 7-X (W7-X) stellarator is to demonstrate integrated reactor potential optimized line. An important element this mission achievement high heating-power and confinement in steady-state operation. Such an plasma operation has not yet been demonstrated represents major scientific goal W7-X. way towards staged. In first phase, called OP 1.1, December 2015-March 2016, a limiter configuration was used. paper, preparation phase as well lessons learned during...
The low-Z oxygen and carbon were the main plasma impurities in Wendelstein 7-X (W7-X) stellarator last experimental campaign with passively cooled graphite divertor. To tackle this issue boronization (Winter et al 1989 J. Nucl. Mater. 162–4 712–23) was applied, which has led to one of achievements campaign: operation at high core densities more than 1020 m−3 hydrogen fueled plasmas due reduced radiation-induced density limit.
Wendelstein 7-X, the world's largest superconducting stellarator in Greifswald (Germany), started plasma experiments with a water-cooled plasma-facing wall 2022, allowing for long pulse operation. In parallel, project was launched 2021 to develop W based divertor, replacing current CFC demonstrate performance of reactor relevant facing materials low tritium retention. The consists two tasks: Based on experience from previous experimental campaigns and improved physics modelling, geometry...
Tungsten has been considered a plasma-facing material in future fusion reactor because of its low sputtering yield and fuel retention. It examined several tokamaks. In stellarators, it recently used for some components. However, addition to high cost, W is difficult machine due hardness brittleness therefore alternative materials the form tungsten heavy alloys are being investigated tests have already performed ASDEX upgrade [1]. WNiFe magnetic, but since magnetization saturates at ∼ 2 Tesla...
Abstract We present a method to geometrically quantify the three magnetic island chains with poloidal mode numbers m = 4, 5, and 6 (referred in this paper as high-iota, standard, low-iota islands, respectively), on which W7-X divertor relies. The focus is comparative study of their detachment performance using series models different physical geometrical complexity, ranging from one- three-dimensional (1D 3D). In particular, it aims identify key elements behind correlation between impurity...
The material transport by erosion and redeposition at the plasma facing wall areas in high temperature experiments has been studied using limiter-like carbon probes with well defined surface deposits depth markers. have exposed scrape-off layer (SOL) of Joint European Torus (JET) during single discharges. For evaluation these a computer program, ERO, developed. calculated erosion-deposition rates for as function distance to last closed flux (LCFS) agree experimental results. 4He JET...
Assembly of the superconducting stellarator Wendelstein 7-X is well advanced, and commissioning device being prepared. A first draft tasks has been developed will be discussed in this paper.
Abstract W7-X completed its plasma operation in hydrogen with island divertor and inertially cooled test unit (TDU) made of graphite. A substantial set plasma-facing components (PFCs), including particular marker target elements, were extracted from the vessel analysed post-mortem. The analysis provided key information about underlying plasma–surface interactions (PSI) processes, namely erosion, transport, deposition as well fuel retention graphite components. net carbon (C) erosion...
The net erosion and deposition pattern of carbon from the Test Divertor Unit (TDU) stellarator W7-X was determined. Special target elements with marker layers consisting about 300 nm molybdenum 5–10 μm on top were used during operational phase OP 1.2a. thicknesses determined by elastic backscattering spectrometry (EBS) using 2.5 MeV protons before after plasma exposure laser-induced breakdown spectroscopy selected exposure. Scanning electron microscopy for investigating surface morphology...
Abstract A set of dedicated marker samples consisting fine-grain graphite as substrate, an interlayer 0.2–0.4 μ m molybdenum (Mo) employed marker, and a 5–10 thick carbon (C) layer on top were installed in Wendelstein 7-X (W7-X) to investigate locally the C erosion deposition. In this study, five individual tiles, vertical divertor element test unit half-module 50, exposed about 40 min plasma predominant standard magnetic configuration first year operation W7-X (OP1.2A), retrieved from...
In 2015, the optimized stellarator Wendelstein 7-X (W7-X) started with operation. The main objective of W7-X is demonstration integrated reactor potential line. An important element this mission achievement high heating power and confinement in steady-state approach to following three steps. First, plasmas were produced a limiter configuration [operation phase (OP 1.1)], then test divertor unit being installed (temporary unit) for next campaign, OP 1.2, before full capability will be...
Observations on confinement in the first experimental campaign optimized Stellarator Wendelstein 7-X are summarized. In this phase W7-X was equipped with five inboard limiters only and thus discharge length restricted to avoid local overheating. Stationary plasmas limited low densities <2–3 · 1019 m−3. With available 4.3 MW ECR Heating core Te ~ 8 keV, Ti 1–2 keV achieved routinely resulting energy time τE between 80 ms 150 ms. For these conditions show characteristics of electron root...