A5053113129- Magnetic confinement fusion research
- Laser-Plasma Interactions and Diagnostics
- Plasma Diagnostics and Applications
- Fusion materials and technologies
- Plasma Applications and Diagnostics
- Physics of Superconductivity and Magnetism
- Particle accelerators and beam dynamics
- Superconducting Materials and Applications
- Atomic and Molecular Physics
- Ionosphere and magnetosphere dynamics
- Laser-induced spectroscopy and plasma
- Nuclear reactor physics and engineering
- Metal and Thin Film Mechanics
- Quantum and electron transport phenomena
- Solar and Space Plasma Dynamics
- Electrohydrodynamics and Fluid Dynamics
- Surface and Thin Film Phenomena
- Analytical Chemistry and Sensors
- Dust and Plasma Wave Phenomena
- Advanced Chemical Physics Studies
- Magnetic properties of thin films
- Mass Spectrometry Techniques and Applications
- Atomic and Subatomic Physics Research
- Cold Atom Physics and Bose-Einstein Condensates
- Electrostatic Discharge in Electronics
Max Planck Institute for Plasma Physics - Greifswald
2016-2024
Max Planck Institute for Plasma Physics
2016-2021
Max Planck Society
2016-2020
Universität Greifswald
2012-2018
Charité - Universitätsmedizin Berlin
2003-2004
Humboldt-Universität zu Berlin
1997-2004
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...
The transport of heavy impurities has been investigated at the Wendelstein 7-X stellarator during core electron root confinement (CERC) experiments. Iron atoms were injected via laser blow-off technique and analyzed by VUV x-ray spectrometers. amount iron does not change global plasma parameters but yields strong enough line radiation for detailed studies based on impurity code STRAHL. latter is supplied with neo-classical diffusion convection profiles from drift kinetic equation solver...
The Charge Exchange Recombination Spectroscopy (CXRS) diagnostic has become a routine on almost all major high temperature fusion experimental devices. For the optimized stellarator Wendelstein 7-X (W7-X), highly flexible and extensive CXRS been built to provide high-resolution local measurements of several important plasma parameters using recently commissioned neutral beam heating. This paper outlines design specifics W7-X system gives examples initial results obtained, including typical...
We develop an analytical expression for the self-energy of infinite-dimensional Hubbard model that is correct in a number different limits. The approach represents generalization iterative perturbation theory to arbitrary fillings. In weak-coupling regime second order interaction U recovered. exact atomic limit. high-energy behavior up 1/${\mathrm{E}}^{2}$ and thereby first four moments spectral density are reproduced correctly. Referring standard strong-coupling moment method, we analyze...
Abstract 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 transitions are independent species and originate from ions with ionization states ranging 14+ 45+ suggesting that this approach can be applied a variety heavy impurities. Moreover, little no passive signal is since energy levels unlikely populated by electron impact...
This paper reports on the design and performance of recently upgraded X-ray imaging spectrometer systems, crystal high resolution spectrometer, installed at optimized stellarator Wendelstein 7-X. High spectra highly ionized, He-like Si, Ar, Ti, Fe as well H-like Ar have been observed. A cross comparison ion electron temperature profiles derived from a spectral fit tomographic inversion shows reasonable match with both spectrometers. The also measured impurity density peaked densities radial...
We present a detailed overview and first results of the new laser blow-off system on stellarator Wendelstein 7-X. The allows impurity transport studies by repetitive controlled injection different tracer ions into plasma edge. A Nd:YAG is used to ablate thin metal film, coated glass plate, with repetition rate up 20 Hz. remote-controlled adjustable optical variation spot diameter enables positioning non-ablated areas target between pulses. During experiments, clear spectral lines from higher...
The capacitively coupled radio frequency plasma at 13.56 MHz in oxygen was systematically studied by 160 GHz Gaussian beam microwave interferometry high temporal resolution (200 ns) and simultaneous laser photodetachment for electron negative ion density analysis. Additionally, spatio-temporally resolved electric probe measurements were performed comparison with interferometry. A low electronegative operation mode found the asymmetric rf discharge. In it shown significant role of metastable...
In this series of two papers, the E-H transition in a planar inductively coupled radio frequency discharge (13.56 MHz) pure oxygen is studied using comprehensive plasma diagnostic methods. The electron density serves as main parameter to distinguish between operation modes. (effective) temperature, which calculated from energy distribution function and difference floating potential, halves during transition. Furthermore, pressure dependency RF sheath extension E-mode implies collisional for...
In this paper, the plasma volume averaged impurity confinement of selected charge states and species has been characterized for Stellarator Wendelstein 7-X (W7-X), covering a wide range atomic charges (Z = 12–44) masses (M 28–184). A comparison experimental findings to theoretical neoclassical turbulent transport expectations suggests, aside from/in addition transport, an additional significant anomalous mechanism, which is not inconsistent with predictions turbulence dominated in agreement...
Abstract In the previous divertor campaign, Wendelstein 7-X (W7-X) device injected 3.6 MW of neutral beam heating power allowing for achievement densities approaching 2 × 10 20 m −3 , and providing first initial assessment fast ion confinement in a drift optimized stellarator. The injection (NBI) system on W7-X is comprised two boxes with space four radio frequency sources each. reported this work was achieved NI21 box. effect combined electron-cyclotron resonance (ECRH) NBI explored through...
The sum rule for the moments of spectral density is discussed single-band Hubbard model. It shown that respecting up to order m = 3 conceptually important a qualitatively correct description quasi-particle band structure in strong-correlation regime. Different analytical approximations self-energy are analyzed with respect their compatibility moment rule. To estimate practical usefulness rule, correlation functions and dynamical quantities determined. results obtained within various...
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>...
This contribution presents experimental results regarding the influence of nanoparticle formation in capacitively coupled radio frequency (13.56 MHz) argon-acetylene plasmas. The discharge is studied using non-invasive 160 GHz Gaussian beam microwave interferometry and optical emission spectroscopy. Particularly, temporal behavior electron density from analyzed compared with changing plasma self-bias voltage caused by formation. periodic particle a cycle duration between 30 s 140 starts an...
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.
A planar inductively coupled RF discharge (13.56 MHz) in argon and oxygen was exemplarily studied using space phase resolved optical emission spectroscopy. The characteristic excitation rate pattern due to the electron heating during sheath expansion found for both gases E-mode. Furthermore, an intensive appears collapse. This is associated with caused by electric field reversal strong electronegativity. transition from E- H-mode may be stepwise or continuous, depending on gas type total...
In this series of two papers we present results about the E-H transition an inductively coupled oxygen discharge driven at radio frequency (13.56 MHz) for different total gas pressures. The mode from low density E-mode to high H-mode is studied using comprehensive plasma diagnostics. measured electron can be used distinguish between operation modes. This paper focuses on determination negative atomic ion and electronegativity by experimental methods global rate equation calculation. As a...
Periodic fluctuations in the frequency range from 0.3 to 3 kHz were experimentally investigated capacitively coupled radio (13.56 MHz) oxygen plasma. The Gaussian beam microwave interferometry directly provides line integrated electron density fluctuations. A system of two Langmuir probes measured floating potential spatially (axial, radial) and temporally resolved. Hence, fluctuation development is mapped within discharge volume a kind breathing no wave propagation. Finally, it was optical...
This contribution presents experimental results about the mode transition of an inductively coupled radio frequency (RF) (13.56 MHz) argon discharge at different total gas pressures. In particular, positive ion saturation current and line integrated electron density are measured by Langmuir probe 160 GHz microwave interferometer, respectively. The strongly depends on pressure can appear stepwise or continuously. space resolved is separately shown for E- H-mode Therewith, dependency RF sheath...
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...
Abstract This contribution presents results of comprehensive investigation the E‐H transition in an inductively coupled radio frequency argon/oxygen discharge at 13.56 MHz. For characterization arrangement, spatial magnetic and electric field components planar coil vacuum are calculated provide information about electron heating region. The used double leads to a radial symmetric distribution. Further, voltage current probe measurements reveal inductivity phase shift between current. As...
Axial and radial profiles of the positive ion saturation current were measured by Langmuir probe diagnostics in a capacitively coupled radio frequency (RF) plasma argon oxygen. Under certain conditions these provide spatial density distribution ions, which corresponds approximately to electron electropositive plasma. Particularly oxygen at low RF power peak appears direction electrode boundary. The axial position s maximum depends on total pressure with ∝ p−1/3, reveals dependence...
This paper reports on the effect of on- and off-axis heating power deposition impurity confinement in purely electron cyclotron resonance heated He plasmas stellarator Wendelstein 7-X. Therefore, transport times τI have been determined after Fe injections by laser ablations monitoring temporal emissivities x-ray imaging spectrometer HR-XIS. A significant increase has observed when changing from to with energy τE being mainly unaffected. In addition, scaling properties respect a variation...