Refine
Year of publication
- 2021 (24) (remove)
Document Type
- Article (15)
- Doctoral Thesis (9)
Has Fulltext
- yes (24)
Is part of the Bibliography
- no (24)
Keywords
- - (13)
- dusty plasma (4)
- Komplexes Plasma (2)
- Wendelstein 7-X (2)
- electron–hole plasma (2)
- 3D (1)
- 4D flow MRI (1)
- 7755384-6 (1)
- ASDEX Upgrade (1)
- Bayes-Verfahren (1)
- Biomolecules (1)
- DIT (1)
- Detachment (1)
- Digital ion trap (1)
- Dirac-cone physics (1)
- Dissertation (1)
- Divertor (1)
- Elektronenstreuung (1)
- FTIR spectroscopy (1)
- Festkörperphysik (1)
- Fusion , Plasma , Plasmaphysik (1)
- Fusionsreaktor (1)
- Heat flux (1)
- Hybridisierungstheorie (1)
- Ion thrusters (1)
- Langmuir probe diagnostics (1)
- Least-squares method (1)
- Lichtstreuung (1)
- L–H transition (1)
- MR-ToF device (1)
- Madden-Julian Oscillation (1)
- Mie-Theorie (1)
- Modell (1)
- N incorporation (1)
- OLR-based MJO Index (1)
- OMI (1)
- PIC (1)
- PWV (1)
- Particle flux (1)
- Photoströme (1)
- Plasma (1)
- Plasmadiagnostik (1)
- Plasmaphysik (1)
- Plasmasonde (1)
- Plasmonik (1)
- Python (1)
- Quadrupole mass filter (1)
- RF mass Spectrometry (1)
- RNS (1)
- Rydberg excitons (1)
- S/XB coefficient (1)
- Seebeck effect (1)
- Sheath transmission coefficient (1)
- Simulation (1)
- Stellarator (1)
- Strikeline (1)
- Ti-Cu-N coating (1)
- Transmission electron microscopy (1)
- WSS (1)
- X-ray diffraction (1)
- X-ray photoelectron spectroscopy (1)
- actin cytoskeleton (1)
- actin quantification (1)
- anti-adhesive surface (1)
- aortic arch (1)
- atherosclerosis (1)
- atmosphere (1)
- atmospheric pressure plasma (1)
- cell spreading (1)
- cell-material interaction (1)
- charge measurement (1)
- climate (1)
- cold physical plasma (1)
- combination therapy (1)
- coupled phonon-plasmon modes (1)
- density limit (1)
- dielectric response (1)
- dust-density waves (1)
- energy-resolved ion mass spectrometry (1)
- flow dynamics (1)
- fluorescence (1)
- food quality (1)
- ftir spectroscopy (1)
- hollow cathode discharge (1)
- inflammatory/immunological response (1)
- intramuscularly implantation (1)
- intraseasonal variation (1)
- laser spectroscopy (1)
- leafy greens (1)
- low-temperature plasma polymerization (1)
- magnetic fields (1)
- magnetron sputtering (1)
- magnetron sputtering discharge (1)
- mapping (1)
- mathematical modeling (1)
- medical gas plasma technology (1)
- melamine-formaldehyde (1)
- microwave-driven discharge (1)
- mouse (1)
- nanowire (1)
- networks (1)
- neural (1)
- non-thermal processing (1)
- oncology (1)
- osteoblasts (1)
- particle (1)
- phase separation (1)
- photocurrent (1)
- plaque characteristics (1)
- plasma-fluorocarbon-polymer (1)
- positively biased anode (1)
- quantum corrections (1)
- quasi-two-dimensional systems (1)
- reactive oxygen species (1)
- ready-to-eat produce (1)
- reconstruction (1)
- scanning ion conductance microscopy (1)
- scattering processes (1)
- separatrix (1)
- similarity scaling (1)
- spin-polarized current (1)
- surface charge sensing (1)
- terahertz ellipsometry (1)
- terahertz spintronics (1)
- terahertz time‐domain spectroscopy (1)
- titanium (Ti) alloys (1)
- tokamak (1)
- topological insulator (1)
- topologische Isolatoren (1)
- tumor immunology (1)
- turbulence (1)
- vision (1)
- weather forecasting (1)
Institute
- Institut für Physik (24) (remove)
Publisher
- IOP Publishing (6)
- MDPI (5)
- Elsevier (1)
- Frontiers Media S.A. (1)
- Software Sustainability Institute (1)
Motiviert durch den Vorschlag einer direkten, optischen Ladungsmessung an Staubteilchen wird die Lichtstreuung an den dielektrischen Kern-Schale-Teilchen tiefgehend untersucht.
Das Streuregime wird durch Analyse des Nah- und Fernfeldes unter Verwendung von Methoden, die für homogene Teilchen entwickelt wurden, eingehend charakterisiert und eine Verallgemeinerung der dazu verwendeten Funktionen auf ein k-fach beschichtetes Teilchen angegeben. Dabei werden die sich im Teilcheninneren manifestierenden Effekte der Hybridisierung der beiden Oberflächenphononen des Kern-Schale-Teilchens herausgearbeitet und visualisiert.
Die vorliegende Untersuchung der unterschiedlichen Kenngrößen ermöglicht ein detailliertes und umfangreiches Verständnis der Lichtstreuung an dielektrischen Kern-Schale-Teilchen und der Art und Weise, wie sich die Hybridisierung der Oberflächenphononen auf diese auswirkt.
Die dabei analysierte Interferenzstruktur des elektromagnetischen Feldes in der Teilchenschale, berechnet mittels der vollen Mie-Rechnung, passt zur Interpretation der optischen Antwort des Kern-Schale-Teilchens mithilfe der Hybridisierungstheorie.
Dieses Hybridisierungsbild und somit die Subsysteme und ihre Wechselwirkung werden in dieser Arbeit aus den analytisch exakten Mie-Koeffizienten heraus präpariert, um die neue Sichtweise mit der alten Mie-Theorie zusammenzubringen.
Die Idee einer spektroskopische Ladungsmessung wird im Hinblick auf die Bestimmung der Wandladung aufgegriffen. Die bisherigen Methoden zur Ladungsmessung sind zwar vielfältig, bieten jedoch nur Zugang zur absoluten Wandladung und liefern keine Informationen über ihre Verteilung senkrecht zur Oberfläche oder über die Dynamik der Aufladung.
Beides wäre jedoch für ein mikroskopisches Verständnis der Plasma-Wand-Wechselwirkung notwendig, sodass die Elektronenenergieverlustspektroskopie zur Ladungsbestimmung vorgeschlagen wird. Die Methode wird zunächst anhand einer lokalen Antworttheorie für verschiedene in die Wand eingesetzte Schichtstrukturen ausgelotet und aufgrund vielversprechender Resultate anschließend mittels der im betrachteten Parameterbereich notwendigen nichtlokalen Antworttheorie eingehend untersucht. Diese Theorie erfasst die Anregung von Resonanzen höherer Moden, die sich als besonders sensitiv auf die zusätzlichen Ladungsträger erweisen. Insgesamt wird ein experimenteller Aufbau mit einer geeigneten, in die Plasmakammerwand einsetzbaren Schichtstruktur vorgeschlagen, mit dem die Wandladung durch Elektronenenergieverlustspektroskopie bestimmt werden könnte.
AbstractWe propose a new scattering mechanism of Rydberg excitons, i.e., those with high principal quantum numbers, namely scattering by coupled LO phonon-plasmon modes, which becomes possible due to small differences in energies of the states due to different quantum defects. Already in very low-density electron–hole plasmas these provide a substantial contribution to the excitonic linewidth. This effect should allow determining plasma densities by a simple line shape analysis. Whenever one expects that low-density electron–hole plasma is present the plasmon induced broadening is of high significance and must be taken into account in the interpretation.
Ion trajectories have been simulated for an assembly of a linear quadrupole ion-filter and a linear Paul trap with additional pin electrodes for MS SPIDOC, a project in preparation for the study of biomolecules by single-particle imaging with X-ray pulses. The ion-optical components are based on digital RF guiding and trapping fields. In order to carefully handle biomolecules over a wide mass-over-charge range, the module presented consists of separate components for filtering and accumulation/trapping in order to select the ions of interest and to convert the beam from a continuous ion source to ion bunches, respectively, as required for the experiments downstream. The present analysis focuses on the transmission efficiency and mass resolving power of the filter, as well as the buffer-gas-pressure-dependent ion capture and thermalization in the trap for the example of a mass-to-charge ratio equivalent to hemoglobin 15+ ions. The resulting optimized ion bunch delivered by the assembly is characterized.
AbstractAnalytical results for the dielectric function in RPA are derived for three-, two-, and one-dimensional semiconductors in the weakly-degenerate limit. Based on this limit, quantum corrections are derived. Further attention is devoted to systems with linear carrier dispersion and the resulting Dirac-cone physics.
Abstract
The anomalous Hall effect (AHE) is a fundamental spintronic charge‐to‐charge‐current conversion phenomenon and closely related to spin‐to‐charge‐current conversion by the spin Hall effect. Future high‐speed spintronic devices will crucially rely on such conversion phenomena at terahertz (THz) frequencies. Here, it is revealed that the AHE remains operative from DC up to 40 THz with a flat frequency response in thin films of three technologically relevant magnetic materials: DyCo5, Co32Fe68, and Gd27Fe73. The frequency‐dependent conductivity‐tensor elements σxx and σyx are measured, and good agreement with DC measurements is found. The experimental findings are fully consistent with ab initio calculations of σyx for CoFe and highlight the role of the large Drude scattering rate (≈100 THz) of metal thin films, which smears out any sharp spectral features of the THz AHE. Finally, it is found that the intrinsic contribution to the THz AHE dominates over the extrinsic mechanisms for the Co32Fe68 sample. The results imply that the AHE and related effects such as the spin Hall effect are highly promising ingredients of future THz spintronic devices reliably operating from DC to 40 THz and beyond.
Three-dimensionally extended dusty plasmas containing mixtures of two particle species of different size have been investigated on parabolic flights. To distinguish the species even at small size disparities, one of the species is marked with a fluorescent dye, and a two-camera video microscopy setup is used for position determination and tracking. Phase separation is found even when the size disparity is below 5%. Particles are tracked to obtain the diffusion flux, and resulting diffusion coefficients are in the expected range for a phase separation process driven by plasma forces. Additionally, a measure for the strength of the phase separation is presented that allows to quickly characterize measurements. There is a clear correlation between size disparity and phase separation strength.
Molecular dynamics simulations of binary dusty plasmas have been performed and their behavior with respect to the phase separation process has been analyzed. Here as well, it is found that even the smallest size disparities lead to phase separation. The separation is due to the force imbalance on the two species and the separation becomes weaker with increasing mean particle size.
In the second part of the thesis, Experiments on self-excited dust-density waves under various magnetic fields have been performed. For that purpose, different dust clouds of micrometer-sized dust particles were trapped in the sheath of a radio frequency discharge. The self-excited dust-density waves were studied for magnetic field strengths ranging from 0 mT to about 2 T. It was observed that the waves are very coherent at the lowest fields (B < 20 mT). At medium fields (20 mT < B < 300 mT), the waves seem to feature a complex competition between different wave modes before, at even higher fields, the waves become more coherent again. At the highest fields (B > 1 T), the wave activity is diminished. The corresponding wave frequencies and wavenumbers have been derived. From the comparison of the measured wave properties and a model dispersion relation, the ion density and the dust charge are extracted. Both quantities show only little variation with magnetic field strength.
This study evaluated the impact of a defined plasma treated water (PTW) when applied to various stages within fresh-cut endive processing. The quality characteristic responses were investigated to establish the impact of the PTW unit processes and where PTW may be optimally applied in a model process line to retain or improve produce quality. Different stages of application of PTW within the washing process were investigated and compared to tap water and chlorine dioxide. Fresh-cut endive (Cichorium endivia L.) samples were analyzed for retention of food quality characteristics. Measurements included color, texture, and nitrate quantification. Effects on tissue surface and cell organelles were observed through scanning electron and atomic force microscopy. Overall, the endive quality characteristics were retained by incorporating PTW in the washing process. Furthermore, promising results for color and texture characteristics were observed, which were supported by the microscopic assays of the vegetal tissue. While ion chromatography detected high concentrations of nitrite and nitrate in PTW, these did not affect the nitrate concentration of the lettuce tissue post-processing and were below the concentrations within EU regulations. These results provide a pathway to scale up the industrial application of PTW to improve and retain quality characteristic retention of fresh leafy products, whilst also harnessing the plasma functionalized water as a process intervention for reducing microbial load at multiple points, whether on the food surface, within the process water or on food-processing surfaces.
This work presents the first experimental investigation of the gas balance on the optimized modular stellarator Wendelstein 7-X (W7-X). A balance of all injected and removed particles and a measurement of internal particle reservoirs allows inference of the bound particle reservoir in the wall, which is of interest due to its effects on plasma density control and fuel retention. Different scenarios of the gas balance are presented with data from the operation campaign 1.2 with an inertially cooled graphite divertor. Both net outgassing and net retention scenarios are presented and W7-X is found to operate stable in a wide range of scenarios with varying wall conditions.
Since fusion experiments are conducted in ultra-high vacuum, suitable gauges are required for total and partial pressure measurement. The challenges and opportunities of the operation of pressure gauges in the steady magnetic field extending beyond plasma pulses are discussed. The performance of newly improved neutral pressure gauges, based on crystal cathode emitters is quantified. These provide improved operational robustness since they can be operated for long periods of time in strong magnetic fields. A crystal cathode setup and and its operation performance is presented along with a fast calibration scheme.
Partial pressure measurements provide additional important information complementing the total neutral pressure measurements, and allowing additional physics insights. As part of this thesis work, a new diagnostic of this kind was implemented on W7-X, the so-called diagnostic residual gas analyzer (DRGA). It provides a wealth of information on various neutral gas species, with a relatively high time resolution - of order a few seconds. The diagnostic setup and its first results are presented in this thesis.
This thesis describes how the data of the Langmuir probes in the Wendelstein 7-X (W7X) Test Divertor Unit (TDU) were evaluated, checked for consistency with other diagnostics and used to analyse plasma detachment.
Langmuir probes are an electronic diagnostic, and were among the first to be used in plasma physics to determine particle fluxes, potentials, temperatures and densities.
W7X is a large, advanced stellarator, magnetic confinement fusion experiment, operated at the Max-Planck-Institut for Plasma Physics(IPP) in Greifswald, Germany.
Its TDU is an uncooled graphite component, shaped and positioned to intercept the convective heat load of the plasma.
Detachment describes a desirable operation state of strongly reduced loads on this component.
The evaluation of Langmuir probe data relies heavily on models of the sheath, formed at the interface between plasma and a solid surface, to infer plasma parameters from the directly measured quantities.
Multiple such models are analysed, generalised, and adapted to our use case.
A detailed comparison is made to determine the most suitable model, as this choice strongly affects the predicted parameters.
Special attention is paid to uncertainties on the parameters, which are determined using a Bayesian framework.
From the inferred parameters, heat and particle fluxes are calculated.
These are also indirectly measured by two other, camera-based diagnostic systems.
Observations are compared to test the validity of assumptions and calculations in the evaluation of all three diagnostics by checking their results for consistency.
The first comparison, with the infrared emission camera system, shows good agreement with theoretical predictions and reported measurements of the sheath transmission factor, for which we derive and measure a value in W7X.
Parameter dependencies in the quality of this agreement hint at remaining issues.
The second comparison, with the Hydrogen alpha photon flux camera system, shows significant discrepancy with expectations.
These are argued to originate from systematic differences in the measurement locations, which are quantified and related to the magnetic topology.
Langmuir probe observations of individual discharges are analysed to discuss conditions under which detachment occurs, transition into that state and fluctuations observed prior to and during it.
A spatial parametrisation of the data is developed and used to facilitate this.
These observations contribute to the larger aim of understanding particle balance control and fusion plasma edge processes.