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#### Institute

- Institut für Physik (156) (remove)

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.

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.

Modern space missions depend more and more on electric propulsion devices for in-space
flights. The superior efficiency by ionizing the feedgas and propelling them using electric
fields with regard to conventional chemical thrusters makes them a great alternative. To
find optimized thruster designs is of high importance for industrial applications. Building
new prototypes is very expensive and takes a lot of time. A cheaper alternative is to rely
on computer simulations to get a deeper understanding of the underlying physics. In order
to gain a realistic simulation the whole system has to be taken into account including the
channel and the plume region. Because numerical models have to resolve the smallest time
and spatial scales, simulations take up an unfeasible amount of time. Usually a self-similarity
scaling scheme is used to greatly speed up these simulations. Until now the limits of this
method have not been thoroughly discussed. Therefore, this thesis investigates the limits
and the influence of the self-similarity scheme on simulations of ion thrusters. The aim
is to validate the self-similarity scaling and to look for application oriented tools to use
for thruster design optimization. As a test system the High-Efficiency-Multistage-Plasma
thruster (HEMP-T) is considered.
To simulate the HEMP-T a fully kinetic method is necessary. For low-temperature plasmas,
as found in the HEMP-T, the Particle-in-Cell (PIC) method has proven to be the best
choice. Unfortunately, PIC requires high spatial and temporal resolution and is hence
computationally costly. This limits the size of the devices PIC is able to simulate as well
as limiting the exploration of a wider design space of different thrusters. The whole system
is physically described using the Boltzmann and Maxwell equations. Using these system
of equations invariants can be derived. In the past, these invariants were used to derive a
self-similarity scaling law, maintaining the exact solution for the plasma volume, which is
applicable to ion thrusters and other plasmas. With the aid of the self-similarity scaling
scheme the computation cost can be reduced drastically. The drawback of the geometrical
scaling of the system is, that the plasma density and therefore the Debye length does not
scale. This expands the length at which charge separation occurs in respect to the system
size. In this thesis the limits of this scaling are investigated and the influence of the scaling
at higher scaling factors is studied. The specific HEMP-T design chosen for these studies is
the DP1.
Because the application of scaling laws is limited by the increasing influence of charge separation with increased scaling, PIC simulations still are computationally costly. Another approach to explore a wider design space is given using Multi-Objective-Design-Optimization
(MDO). MDO uses different tools to generate optimized thruster designs in a comparatively
short amount of time. This new approach is validated using the PIC method. During this
validation the drawback of the MDO surfaces. The MDO calculations are not self-consistent
and are based on empirical values of old thruster designs as input parameters, which not
necessarily match the new optimized thruster design. By simulating the optimized thruster
design with PIC and recalculate the former input parameters, a more realistic thruster design is achieved. This process can be repeated iteratively. The combination of self-consistent
PIC simulations with the performance of MDO is a great way to generate optimized thruster
designs in a comparatively short amount of time. The proof of concept of such a combination
is the pinnacle of this thesis.

The first Therapeutic ROS and Immunity in Cancer (TRIC) meeting was organized by the excellence research center ZIK plasmatis (with its previous Frontiers in Redox Biochemistry and Medicine (FiRBaM) and Young Professionals’ Workshop in Plasma Medicine (YPWPM) workshop series in Northern Germany) and the excellence research program ONKOTHER-H (Rostock/Greifswald, Germany). The meeting showcased cutting-edge research and liberated discussions on the application of therapeutic ROS and immunology in cancer treatment, primarily focusing on gas plasma technology. The 2-day hybrid meeting took place in Greifswald and online from 15–16 July 2021, facilitating a wide range of participants totaling 66 scientists from 12 countries and 5 continents. The meeting aimed at bringing together researchers from a variety of disciplines, including chemists, biochemists, biologists, engineers, immunologists, physicists, and physicians for interdisciplinary discussions on using therapeutic ROS and medical gas plasma technology in cancer therapy with the four main sessions: “Plasma, Cancer, Immunity”, “Plasma combination therapies”, “Plasma risk assessment and patients studies”, and “Plasma mechanisms and treated liquids in cancer”. This conference report outlines the abstracts of attending scientists submitted to this meeting.

Surface Stoichiometry and Depth Profile of Tix-CuyNz Thin Films Deposited by Magnetron Sputtering
(2021)

Organic molecules are the carbon-based complex of several atoms, is an innovative and essential element to create nano-structural platforms, as a building block in the
field of organic electronics and organic spintronics. Because of its variety and functionality via widely studied synthetic methods, molecules have played an important role in electronics as not only a transport channel in bulk form but also a tuning layer
at the interface of hetero structures. The potential of molecular layers has also stood out in spintronics, owing to its mass-low composition producing long spin life time.
Organic materials can be employed in spintronics applications, benefiting from their low cost, ease of processing, and chemical tunability. Beyond this advantage, the configuration
of molecules on a metal film displays unique phenomena as it can control the molecular spins and interfacial coupling between them, resulting in the emergence
of molecular spinterface.
This thesis work focuses on identifying the interfacial properties between the ferromagnet and the Phenalenyl (PLY) based metal complexes. The growth morphology study of the copper-phenalenyl Cu-PLY based molecules influence the electronic coupling between the molecular layer and the ferromagnet. Zinc- Phenalenyl (ZMP) molecule already have been studied [1] by demonstrate the formation of a spinterface,
resulting interface magneto resistance (IMR) close to room temperature. The
spinterface formation leads to the unique property, that a magnetic tunnel junction
with a ZMP barrier requires only one ferromagnetic metal layer, while the other ferromagnetic layer is formed in the organic barrier directly at the ferromagnet/organic
barrier interface. Here we compare Phenaleny, Copper-Phenaleny Cu-PLY and Zincmethyl- phenaleny molecule based MTJ electrical and magnetic properties which will
be suitable for tunnel barrier and can be used for stable memory devices. We tune the magnetic property of ferromagnet and forma hybrid interface without any oxide layers in between the ferromagnet and molecular layers. The tuning of magnetic properties
via the molecular approach will certainly extend versatile functionalities of organic spinterfaces.

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.

Development of an Electrostatic Ion Beam Trap for Laser Spectroscopy of Short-lived Radionuclides
(2021)

Due to its high accuracy and resolution, collinear laser spectroscopy (CLS) is a powerful tool to measure nuclear ground state properties such as nuclear spins, electromagnetic moments and mean-square charge radii of short-lived radionuclides. Performing CLS with fast beams (>30 keV) provides an excellent spectral resolution approaching the natural linewidth. However, its fluorescence-light detection limits its successful application to nuclides with yields of more than several 100 to 10,000 ions/s, depending on the specific case and spectroscopic transition. To extend its reach to the most exotic nuclides with very low production yields far away from stability, more sensitive methods are needed. For this reason, the novel Multi Ion Reflection Apparatus for CLS (MIRACLS) is currently under development at ISOLDE/CERN. This setup aims to combine the high resolution of conventional fluorescence based CLS with a high experimental sensitivity, enhanced by a factor of 30 to 700 depending on the mass and lifetime of the studied nuclide. By repetitively reflecting the ion beam between the electrostatic mirrors of an electrostatic ion beam trap, often also called Multi-Reflection Time of Flight (MR-ToF) device, the laser beam probes the ion bunch during each revolution. Therefore, the observation time is extended and the experimental sensitivity is enhanced compared to conventional single-passage CLS. As part of this thesis, a MIRACLS proof-of-principle apparatus has been constructed around an MR-ToF system, operating at ~1.5 keV beam energy, which has been upgraded for the purpose of CLS. The goal of this setup is to demonstrate the potential of the MIRACLS concept, to benchmark simulations that are employed to design a future device operating at 30 keV, and to further develop the technique. For this purpose, CLS measurements with ions of stable magnesium and calcium isotopes are performed. This data serves to characterise the performance of the new method, especially in terms of gain in sensitivity and measurement accuracy.

In this thesis, the transport properties of topological insulators are investigated. In contrast to trivial insulators, topological insulators possess conducting boundary states which cross the bulk energy gap that separates the highest occupied electronic band from the lowest unoccupied band. The materials used in this thesis are three-dimensional topological insulators with time-reversal symmetry. Their associated helical surface states are protected against elastic backscattering by Kramers degeneracy. The unique properties of the helical surface states can be utilized to generate spin-polarized currents at the surface of topological insulators and to control their propagation direction. This makes them a promising material class for the field of spintronics.
Here, we perform photocurrent scans of topological insulator Hall bar and nanowire devices. From these measurements, we obtained two-dimensional maps of the polarization-independent and helicity-dependent components of the photocurrents.
We find that the polarization-independent component is dominated by the Seebeck effect and thus driven by thermoelectric currents. On the other hand, the helicity-dependent component is driven by the spin-polarized currents that emerge from the topologically non-trivial helical surface states via the circular photogalvanic effect.
First and foremost, our experiments demonstrate that topological insulator nanowires provide a promising platform for the generation of spin-polarized currents, whose direction can be controlled via the helicity of the excitation light. They also highlight the importance of analysing the spatial distribution of the photocurrent, as we observe a strong enhancement of the spin-polarized current and the thermoelectric current at the interface between the nanowire and the metallic contacts. As our analysis shows, the thermoelectric current is enhanced by the Schottky effect and the spin-polarized current is amplified by the spin Nernst effect. In addition, the spin Nernst effect is also present in Hall bar devices and manifest as an enhancement of the spin-polarized current along the Hall bar sides.

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.

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.

In this thesis, I present work motivated, in part, by a series of upcoming laboratory experiments (APEX), which seeks to uncover some of the inner workings of turbulence and stability in electron- positron plasmas in closed field-line systems. I present the results of several distinct, but connected, problems addressing the theory of electron-positron plasmas.
This work is partitioned into several parts, which loosely correspond to different particulars of the APEX experiment and the different theoretical physics problems which reside within.
I begin with the derivation of a kinetic theory for plasmas which are optically thin to cyclotron emission, as indeed, experimental pair plasmas are expected to be. The results of this section include: (1) the derivation of a general kinetic theory of cyclotron radiation in electron-ion plasmas; (2) a calculation showing that cyclotron emission results in strongly anisotropic distribution functions on the radiation timescale; (3) calculation of the evolution of the distribution function under collisional scattering which, in the absence of any radiation terms, acts to drive the plasma towards a Maxwellian; (4) generalisation of this theory to more exotic geometries; (5) specialisation of this theory to pair plasmas of experimental interest; and (6) presentation of the applications and the limitations of this theory.
The second project is primarily concerned with non-neutral plasmas. We begin with gyrokinetic theory and a novel extension of this theoretical framework to plasmas with arbitrary degree of neutrality in straight field-line geometry. I go on to discuss the gyrokinetic stability theory of such plasmas in this simplified geometry. I conclude this project with a discussion of some further
nuances in the theory of singly-charged non-neutral plasmas, this time concerning global features. Namely, I declare an interest in the equilibria such plasmas might be able to attain.
The final project pertains to plasmas which are in state of Maxwellian equilibrium i.e., electron- positron plasmas with sufficiently large number densities of each species to attain a stationary quasineutral plasma. To this end, I present gyrokinetic flux-tube simulations of electron-positron plasmas in complex, and experimentally relevant, magnetic geometries on the road towards a study of gyrokinetic turbulence. The results of this work include: (1) the first simulations of electron- positron plasmas in a stellarator and ring-dipole geometry; (2) an analytic theory of trapped particle modes in electron-positron plasmas, a result which can also be verified numerically; and (3) extension of several important theoretical results in electron-positron plasmas to experimentally relevant geometries. The culmination of this project is the roadmap ahead towards demonstration of the so-called “inward pinch” effect in electron-positron plasmas in a magnetic Z-pinch.

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.

Abstract
To suit a wide variety of space mission profiles, different designs of ion thrusters were developed, such as the High‐Efficiency‐Multistage‐Plasma thrusters (HEMP‐T). In the past, the optimization of ion thrusters was a difficult and time‐consuming process and evolved experimentally. Because the construction of new designs is expensive, cheaper methods for optimization were sought‐after. Computer‐based simulations are a cheap and useful method towards predictive modelling. The physics in HEMP‐T requires a kinetic model. The Particle‐in‐Cell (PIC) method delivers self‐consistent solutions for the plasmas of ion thrusters, but it is limited by the high amount of computing time required to study a specific system. Therefore, it is not suited to explore a wide operational and design space. An approach to decrease computing time is self‐similarity scaling schemes, which can be derived from the kinetic equations. One specific self‐similarity scheme is investigated quantitatively in this work for selected HEMP‐Ts, using PIC simulations. The possible application of the scaling is explained and the limits of this approach are derived.

Electrostatic forces at the cell interface affect the nature of cell adhesion and function; but there is still limited knowledge about the impact of positive or negative surface charges on cell-material interactions in regenerative medicine. Titanium surfaces with a variety of zeta potentials between −90 mV and +50 mV were generated by functionalizing them with amino polymers, extracellular matrix proteins/peptide motifs and polyelectrolyte multilayers. A significant enhancement of intracellular calcium mobilization was achieved on surfaces with a moderately positive (+1 to +10 mV) compared with a negative zeta potential (−90 to −3 mV). Dramatic losses of cell activity (membrane integrity, viability, proliferation, calcium mobilization) were observed on surfaces with a highly positive zeta potential (+50 mV). This systematic study indicates that cells do not prefer positive charges in general, merely moderately positive ones. The cell behavior of MG-63s could be correlated with the materials’ zeta potential; but not with water contact angle or surface free energy. Our findings present new insights and provide an essential knowledge for future applications in dental and orthopedic surgery.

In this work, studies with respect to the exhaust problem were performed
in the stellarator experiment Wendelstein 7-X with different target concepts and different magnetic field geometries. Different infrared cameras were used to study the heat flux from the plasma onto the PFC. In the first publication, the limiter set-up was used with a simpler magnetic topology in the plasma edge. The radial fall-off of the parallel heat flux for inboard limiters in W7-X shows, similar to inboard limiters in tokamaks, two different radial fall-off lengths, a short (narrow) one, characterizing the near-SOL, and a long (broad) characterizing the far-SOL. For the far-SOL, the heating power and connection length have been identified as the main scaling parameters, while for the near-SOL, the electron temperature close to the LCFS has been identified as the main scaling parameter. The two fall-off lengths differ by a factor 10, and the found scalings for both regimes differ from known models and experimental scalings in tokamaks. A turbulent-driven feature was discussed in the publication as a possible explanation for the behavior of the fall-off length in W7-X.
The gained information and data have been further used to support many
other publications, covering the symmetry of the heat loads, the
energy balance of the machine, and seeding experiments.
The heat exhaust in W7-X with an island divertor was studied in the second
and third publication. Definitions of parameters such as peaking factor and
wetted area were applied for the heterogeneous heat flux pattern on the
W7-X divertor. It was shown that the island divertor concept is capable
of spreading out the heat efficiently, resulting in large wetted areas of up to 1.5 m2. The reached values for the wetted area are comparable to the ones of the larger tokamak JET but with a much smaller ratio of wetted
area to the area of the last closed flux surface. Furthermore, a positive
scaling of the wetted area with the power in the SOL was observed. This
scaling is beneficial for future reactors but needs further investigation of the involved transport processes. The peaking factor (discussed in the second publication) describes how concentrated the heat load is within the region of the strike line. It was shown that this factor is decreasing for increasing densities without affecting the wetted area. The present work paves the way for further analysis of the transport processes of the heat flux towards the island divertor of Wendelstein 7-X.

The active screen plasma nitrocarburizing (ASPNC) technology is a state-of-the-art plasma-assisted heat treatment for improving surface hardness and wear resistance of metallic workpieces based on thermochemical diffusion. In comparison to conventional plasma nitrocarburizing, the use of an active screen (AS) improves thermal homogeinity at the workload and reduces soot formation. Further it can serve as a chemical source for the plasma processes, e.g. by use of an AS made of carbon-fibre reinforced carbon. This compilation of studies investigates the plasma-chemical composition of industrial- and laboratory-scale ASPNC plasmas, predominantly using in-situ laser absorption spectroscopy with lead-salt tuneable diode lasers, external-cavity quantum cascade lasers, and a frequency comb. In this way the temperatures and concentrations of the dominant stable molecular species HCN, NH3, CH4, C2H2, and CO, as well as of less prevelant species, were recorded as functions of e.g. the pressure, the applied plasma power, the total feed gas flow and its composition. Additionally, the diagnostics were applied to a chemically similar plasma-assisted process for diamond deposition.
Resulting from this thesis are new insights into the practical application of an AS made of CFC, the plasma-chemistry involving hydrogen, nitrogen, and carbon, and the particular role of CO as an indicator for reactor contamination. The effect of the feed gas composition on the resulting nitrogen- and carbon-expanded austenite layers was proven by combination of in-situ laser absorption spectroscopy with post-treatment surface diagnostics. Furthermore this work marks the first use of frequency comb spectroscopy with sub-nominally resolved Michelson interferometry for investigation of a low-pressure molecular discharge. This way the rotational bands of multiple species were simultaneously measured, resulting in temperature information at a precision hitherto not reached in the field of nitrocarburizing plasmas.

Es wurde eine Methode zur Herstellung ultradünner Filme aus Metall bzw. metallischen Verbindungen (Legierungen) etabliert. Die Struktur und die physikalischen Eigenschaften der Filme wurden untersucht. Die entwickelte Präparationsmethode beruht auf induzierter Filmkontraktion nach erzwungener Benetzung (iFCaFW). Die Filme bestehen aus ultradünnen vertikal heterostrukturierten Multischichten (2D-VHML), sie entstehen durch den Beschichtungsvorgang und bestehen aus jeweils einer nm-dicken metallischen Schicht (M) eingebettet zwischen zwei Metall(hydr)oxidschichten (MOxHy) im nm- bis sub-nm Bereich. Dieser vertikal heterostrukturierte Aufbau wurde bei allen untersuchten Filmmaterialien beobachtet. Alle in dieser Arbeit vorgestellten Schichtsysteme wurden unter atmosphärischem Druck hergestellt. Es konnten Substrate aus Silicium und Muskovit sowie aus Borosilikat- und Kalk-Natron-Glas (Objektträger) beschichtet werden. Jede, aus flüssigem Metall bzw. flüssiger Legierung hergestellte Schicht verfügt über eine feste (Hydr)oxidschicht an der Luftgrenzfläche. Diese feste (Hydr)oxidschicht fungiert als Substrat für die nächste darüber aufgebrachte Schicht aus flüssigem Metall bzw. flüssiger Legierung. Somit entstehen vertikal heterostrukturierte Multischichten durch identische Wiederholung des Beschichtungsvorgangs. Dies ist eine innovative und vergleichsweise umweltfreundliche Methode, um transparente, elektrisch leitfähige und lateral homogene nm-dünne ein- oder mehrschichtige Metallfilme herzustellen. Verwendet wurden Metalle mit sehr niedriger Schmelztemperatur (kleiner als 300 °C), wie Bismut, Gallium, Indium, Zinn und ihre Legierungen. Die hohe Oberflächenspannung der geschmolzenen Metalle und Legierungen sowie die Adhäsion mit der die (Hydr)oxidhaut dieser Metalle und Legierungen auf verschiedenen Substraten haftet ermöglicht die Beschichtungsmethode.

This thesis contains studies on a special class of topological insulators, so called anomalous Floquet topological insulators, which exclusively occur in periodically driven systems. At the boundary of an anomalous Floquet topological insulator, topologically protected transport occurs even though all of the Floquet bands are topologically trivial. This is in stark contrast to ordinary topological insulators of both static and Floquet type, where the topological invariants of the bulk bands completely determine the chiral boundary states via the bulk-boundary correspondence. In anomalous Floquet topological insulators, the boundary states are instead characterized by bulk invariants that account for the full dynamical evolution of the Floquet system.
Here, we explore the interplay between topology, symmetry, and non-Hermiticity in two-dimensional anomalous Floquet topological insulators. The central results of this exploration are (i) new expressions for the topological invariants of symmetry-protected anomalous Floquet topological phases which can be efficiently computed numerically, (ii) the construction of a universal driving protocol for symmetry-protected anomalous Floquet topological phases and its experimental implementation in photonic waveguide lattices, (iii) the discovery of non-Hermitian boundary state engineering which provides unprecedented possibilities to control and manipulate the topological transport of anomalous Floquet topological insulators.

Experience in the construction of optimized stellarators shows the coil system is a significant challenge. The precision necessary allow the generation of accurate flux surfaces in recent experiments affected both cost and schedule negatively. Moreover, recent experiments at Wendelstein 7-X have shown that small field corrections were necessary for the operation of specific desired magnetic configurations. Therefore, robust magnetic configurations in terms of coil geometry and assembly tolerances have a high potential to facilitate swifter and less expensive construction of future, optimized stellarators. We present a new coil optimization technique that is designed to seek out coil configurations that are resilient against 3D coil displacements. This stochastic version of stellarator coil optimization uses the sampling average approach to incorporate an iterative perturbation analysis into the optimization routine. The result is a robust magnetic configuration that simultaneously reproduces the target magnetic field more accurately and leads to a better fusion performing coil configuration.

The non-renewable energy sources coal, oil and natural gas that contribute the major share of the world's energy, will be running out in the next 40-80 years. With the growing energy demands especially in developing countries, which is likely to surpass that of the developed countries in next 50 years, an alternate energy source is the need to the hour. The nuclear fusion energy is foreseen as one of the potential candidates to solve the current global energy crisis. One of the major challenges faced by the fusion community is the problem of power exhaust. With the larger fusion devices to be built in the future, the heat load on the plasma facing components are expected to grow higher. The present work explores two numerical studies performed on the Wendelstein 7-X, the world's largest stellarator type fusion device, to cope with this problem.
The first project on `'Numerical Studies on the impact of Connection Length in Wendelstein 7-X'' identifies magnetic configuration with long connection lengths, which could bring down the peak heat fluxes onto the divertor to manageable levels, by greater role of cross-field transport which may assist to get a wider heat deposition profile. The second project on `'Development of Heating Scenario to Reduce the Impact of Bootstrap Currents in Wendelstein 7-X'' advocates a novel self-consistent approach to reach high plasma density at full heating power without overloading the divertor during the transient phase of the evolution of the toroidal plasma current, by controlling two parameters; density and power. The aim of both the projects is to contribute to tackling the challenge of the tremendous power exhaust from fusion plasma which, if solved, will be a large step closer to a fusion power plant.

An experimental investigation of particle parallel flows has been carried out at Wendelstein 7-X (W7-X), one of the most advanced stellarators in the world. The studies are restricted to the outermost plasma region, the scrape-off layer (SOL), which is shaped to tackle the exhaust problem in vision of future fusion reactors based on plasma magnetic confinement. The aim of the measurements is to set the basis for a physics analysis of the SOL dynamics by obtaining direct information on convective heat transport, together with the assessment of the predominant flow directions of the main plasma ions and of fusion-products or wall-released impurities. In this way, a better comprehension of the interplay between the transport parallel and perpendicular to the SOL field lines can be achieved, contributing to the understanding of the effectiveness of the island divertor configuration.
The chosen instrument for the experimental studies is the Coherence Imaging Spectroscopy (CIS) diagnostic, a camera-based interferometer capable of measuring 2D Doppler particle flows associated with a selected visible line from the plasma. The diagnostic is distinguished by its high time resolution and spatial coverage, allowing the visualisation and measurements of flow velocities for a full module of W7-X simultaneously. A CIS diagnostic has been fully designed for W7-X with an improved level of accuracy achieved thanks to the implementation of a new calibration source, a continuous-wave-emission tunable laser. The laser allowed a full characterization of the diagnostic and a frequent precise calibration, making the CIS system reliable for parallel flow investigations during the operational campaign OP1.2. The validity and importance of the CIS measurements have been further confirmed with dedicated simulation of the SOL plasma parameters by the EMC3-EIRENE code, and by comparisons with other edge diagnostics. The CIS results show the effects related to dynamical changes in the SOL due to impurity gas puffs or the development of a plasma current. Moreover, CIS can be used as a powerful tool to test the limits of the current theoretical models, for example in the case of forward and reversed field experiments.

Barrier corona (BC) arrangements are employed in different plasma-based applications such as material surface and exhaust gas treatments. However, a comprehensive study about the discharge behavior and properties in such strongly asymmetric arrangements is still missing. This dissertation is devoted to the detailed investigation of single microdischarges (MDs) in a sinusoidally driven BC discharge in air at atmospheric pressure. The discharge arrangement consist of a sharp metal pin and a dielectric-covered hemispherical electrode. It is the first study of volume BC discharges, in which phasially-resolved spatio-temporal development of the MDs are recorded using a multi-dimensional time-correlated single photon counting (TC-SPC) technique. The morphology of the MDs is recorded using an ICCD camera. A voltage probe and a current probe are employed to measure the applied voltage and current pulses. Furthermore, phase-resolved current measurements and statistical studies of current pulse amplitudes are realized using an oscilloscope.
Due to the asymmetric geometry and material of the electrodes, discharge behavior in the two polarities of the applied sinusoidal voltage is significantly different. For the voltage amplitude being applied, mostly two MDs appear in the anodic pin half-cycles. It is observed that the breakdown mechanism in both MDs is a positive streamer starting near the anode, similar to the single MDs in symmetric dielectric barrier discharges (DBDs). However, the second MDs have different properties, such as longer duration of the bulk plasma and broader current pulses. It is considered that the differences are mainly due to the positive surface charges deposited by the first MDs on the dielectric. It is proposed, for the first time, that the current pulse derivative maximum corresponds to the arrival of the streamer head at the cathode surface. This is used to synchronize the spatio-temporal development of the MDs with their current pulses. The accuracy of the synchronization is limited to the rise-time of the current probe (350 ps). In each cathodic pin half-cycle, only one major MD appears. The appearance and amplitude of the MDs are more erratic compared to the anodic pin polarity. The TC-SPC recordings show that the MDs appearing at low applied voltages have a similar spatio-temporal development to the MDs of the anodic pin polarity. On the other hand, at high applied voltages a development similar to transient sparks, i.e. a double-streamer starting near the tip of the pin (cathode), is observed. The statistical study shows that in DBD-like MDs the current pulse amplitude is not dependent on the appearance phase (or applied voltage), but this is not the case for the transient sparks.
Since BC reactors are also used for air cleaning, a set of experiments is done with 35 ppm toluene additive. It is observed that adding toluene results in 500~V lower breakdown voltage. Hence, the discharge in the presence of toluene is operated under over-voltage condition, resulting in stronger MDs in the anodic pin, and earlier-appearing as well as weaker MDs in the cathodic pin half-cycles.
The results of this dissertation about the spatio-temporal development and statistical behavior of the single MDs are foreseen to be employed in the study and optimization of plasma reactors, such as "Stacked DBD Reactor," which are developed for exhaust gas and material surface treatment. Furthermore, the results are a benchmark for the study of a novel discharge arrangement with a rotating dielectric electrode.

Anomalous Nernst effect and three-dimensional
temperature gradients in magnetic tunnel junctions
(2018)

The Madden–Julian oscillation (MJO) is a major
source of intraseasonal variability in the troposphere. Recently, studies have indicated that also the solar 27-day variability could cause variability in the troposphere. Furthermore, it has been indicated that both sources could be linked, and particularly that the occurrence of strong MJO events could be modulated by the solar 27-day cycle. In this paper, we analyze whether the temporal evolution of the MJO phases could also be linked to the solar 27-day cycle. We basically count the occurrences of particular MJO phases as a function of time lag after the solar 27-day extrema in about 38 years of MJO data. Furthermore, we develop a quantification approach to measure the strength of such a possible relationship and use this to compare the behavior
for different atmospheric conditions and different datasets, among others. The significance of the results is estimated based on different variants of the Monte Carlo approach, which are also compared. We find indications for a synchronization between the MJO phase evolution and the solar 27-day cycle, which are most notable under certain conditions: MJO events with a strength greater than 0.5, during the easterly phase of the quasi-biennial oscillation, and during boreal winter. The MJO appears to cycle through its eight phases within two solar 27-day cycles. The phase relation between the MJO and the solar variation appears to be such that the MJO predominantly transitions from phase 8 to 1 or from phase 4 and 5 during the solar 27-day minimum. These results strongly depend on the MJO index used such that the synchronization is most clearly seen when using univariate indices like the OLR-based MJO index (OMI) in the analysis but can hardly be seen with multivariate indices like the real-time multivariate MJO index (RMM). One possible explanation could be that the synchronization pattern is encoded particularly in the underlying outgoing longwave radiation (OLR) data. A weaker dependence of the results on the underlying solar proxy is also observed but not further investigated. Although we think that these initial indications are already worth noting, we do not claim to unambiguously prove this relationship in the present study, neither in a statistical nor in a causal sense. Instead, we challenge these initial findings
ourselves in detail by varying underlying datasets and methods and critically discuss resulting open questions to lay a solid foundation for further research.

We report on the effect of solar variability at the 27-day and the 11-year timescales on standard phase height measurements in the ionospheric D region carried out in central Europe. Standard phase height corresponds to the reflection height of radio waves (for constant solar zenith distance) in the ionosphere near 80 km altitude, where NO is ionized by solar Lyman radiation. Using the superposed epoch analysis (SEA) method, we extract statistically highly significant solar 27-day signatures in standard phase heights.
The 27-day signatures are roughly inversely correlated to solar proxies, such as the F10.7 cm radio flux or the Lyman-flux. The sensitivity of standard phase height change to solar forcing at the 27-day timescale is found to be in good agreement with the sensitivity for the 11-year solar cycle,suggesting similar underlying mechanisms. The amplitude of the 27-day signature in standard phase height is larger duringsolar minimum than during solar maximum, indicating that the signature is not only driven by photoionization of NO.We identified statistical evidence for an influence of ultra-long planetary waves on the quasi 27-day signature of standard phase height in winters of solar minimum periods.

With this thesis, studies which form the bedrock for the long term goal of first wall heat load control and optimization for the advanced stellarator Wendelstein 7-X are developed, described and put into context. It is laid out how reconstruction of features of the edge magnetic field from plasma facing component heat loads is an important first step and can successfully be achieved by artificial neural networks. A detailed study of plasma facing component heat load distribution, potential overloads and overload mitigation possibilities is made in first order approximation of the impact of the main plasma dynamic effects.

This thesis describes recent developments in multi-reflection time-of-flight mass spectrometry (MR-ToF MS) with ions exhibiting large masses and mass differences at an MR-ToF setup at the University of Greifswald. A series of in-trap manipulation techniques to selectively retain or eject ion bunches of multiple species with disparate mass-to-charge ratios is investigated. These highlight the possibility to correct long-term flight-time drifts using a reference ion species far away in mass from the species of interest and also the ability to use such a pair to perform single-reference precision mass determinations. In both cases, the results obtained with disparate-mass ion pairs are comparable to those known from operation with isobaric species.
In addition, an in-trap photoexcitation technique is developed and applied to study the dissociation behavior of atomic bismuth clusters (systems of some number of bismuth atoms). Compared to previous works by other groups, the probed cluster-size range is expanded for both ion polarities, resulting in a more comprehensive picture of the underlying dissociation pathways. The known significance of neutral-tetramer breakoff is confirmed, however, evidence is also found for the loss of larger neutral fragments.
Lastly, the principle of tandem high-resolution MR-ToF MS is introduced. This new method allows the study of the change in dissociation behavior of the cationic bismuth octamer resulting from substituting one of its atoms for lead. It is found that the lead-doping opens new preferential fragmentation pathways that outstrip the dominant tetramer breakoff for this specific precursor cluster size. As a first proof-of-principle experiment, the case of the cationic octamer shows that tandem MR-ToF MS is well-suited for the investigation of compound clusters.

The importance of ion propulsion devices as an option for in-space propulsion of space
crafts and satellites continues to grow. They are more efficient than conventional chemi-
cal thrusters, which rely on burning their propellant, by ionizing the propellant gas in a
discharge channel and emitting the heavy ions at very high velocities. The ion emission
region of a thruster is called the plume and extends several meters axially and radially
downstream from the exit of a thruster. This region is particularly important for the effi-
ciency of a thruster, because it determines energy and angular distribution of the emitted
ions. It also determines the interaction with the carrier space craft by defining the electric
potential shape and the fluxes and energies of the emitted high energy ions, which are the
key parameters for sputter erosion of satellite components such as solar panels. Developing
new ion thrusters is expensive because of the high number of prototypes and testing cycles
required. Numerical modeling can help to reduce the costs in thruster development, but
the vastly differing length and time scales of the system, particularly the large differences of
scales between the discharge chamber and the plume, make a simulation challenging. Often
both regions are considered to be decoupled and are treated with different models to make
their simulation technically feasible. The coupling between channel and plume plasmas and
its influence on each other is disregarded, because there is no interaction between the two
regions. Therefore, this thesis investigates the physical effects which arise from this cou-
pling as well as models suitable for an integrated simulation of the whole coupled problem
of channel and plume plasmas. For this purpose the High Efficiency Multistage Plasma
Thruster (HEMP-T) ion thruster is considered.
For the discharge channel plasma, a fully kinetic model is required and the Particle-in-Cell
(PIC) method is applied. The PIC method requires very high spatial and temporal resolu-
tions which makes it computationally costly. As a result, only the discharge channel and the
near-field plume close to the channel exit can be simulated. In the channel, the results show
that electrons are magnetized and follow the magnetic field lines. The orientation of the
magnetic field there is mostly parallel to the symmetry axis and the channel walls which re-
sults in a high parallel electron transport and leads to a flat electric potential and a reduced
plasma-wall sheath. Only at the magnetic cusps, which are characteristic of HEMP-Ts the
electrons are guided towards the wall, with ions following due to quasineutrality, where a
classical plasma-wall sheath develops. The ion-wall contact is thus limited to the cusp re-
gion. The small radial drop of the potential towards the wall gives rather low energies of
ions impinging at the wall and minimizes erosion in the HEMP-T.
In the near-field plume, which extends from the thruster exit plane to some centimeters
downstream, the ion emission characteristics is defined. The ratio of radial and axial elec-
tric field components in this region determines the ion emission angle which should be
minimized for maximum thruster efficiency. The plasma discharge in the channel produces
high plasma densities and the subsequent drop from plasma to vacuum potential occurs
further downstream for higher densities. This increases the ratio of radial and axial electric
field components because the plasma expands radially outside of the confinement from the
dielectric discharge channel walls. The potential structure in the near-field plume impacts
also the supply of electrons for the channel discharge because the electrons enter the channel
from the plume. An effect which arises from this coupling is the breathing mode oscilla-
tion. It is an oscillation which is observed in all plasma quantities and is located near the
thruster exit. The oscillation frequency measured in the simulation is in good agreement
with a predator-prey estimate which validates this ansatz. However, the electron tempera-
ture, assumed constant in the predator-prey model, correlates inversely with the oscillation,
i.e. it is minimal at the current maximum and vice versa, which contributes to the observed
oscillations. Because of the oscillation of the plasma number density, the potential drop also
oscillates in the exit region and thus the ratio of radial to axial electric field components,
which results in the oscillation of the mean ion emission angle.
Regarding suitable models for a combined simulation of channel and plume plasmas, the
PIC model for channel and near-field plume is explicitly coupled to a hybrid fluid-PIC
model for the plume. The latter treats the electrons as a fluid, hence increasing the effective
spatial and temporal resolutions which can be applied in the plume simulations at the cost
of reduced accuracy of the electron model. Plasma densities decrease by two orders of
magnitude two meters downstream from the channel exit. The explicitly coupled kinetic
and hybrid PIC models are well suited for the computation of a HEMP-T and its plume
expansion, but they disregard the coupling of channel and plume plasmas for which other
methods are necessary. For this purpose a new approach is presented with a proof-of-
principle validation. The limited spatial resolution in the plume can be overcome with the
mesh-coarsening method, which increases the resolution in regions of low plasma density
without numerical artifacts. Sub-cycling for the electrons in the plume can then be used
to increase the temporal resolution in the plume. The combination of both methods, called
the sub-cycling mesh-coarsening (SMC) algorithm in the scope of this work, promises high
savings in computational cost which can make a combined simulation of plume and channel
plasmas feasible.

In this doctoral thesis, algorithms are presented that are designed for the investigation in the mesopause region between the upper Mesosphere and Lower Thermosphere (MLT). The photochemical models are proposed and applied to represent the oxygen airglow and the oxygen photochemistry in the MLT. Atomic oxygen, O, in the ground state, O(3P), is of special interest because it is a reactive trace gas actively contributing to the Earth’s airglow. The retrievals of O(3P) concentrations, [O(3P)], are based on the nightglow time series of the green line emission measured remotely as in the first part of this thesis and the individual profiles of multiple nightglow emissions of O and molecular oxygen (O2) measured in situ as in the second part of this thesis. To process the complete spectral time series measured by using the satellite-borne instrument SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY), an intricate set of algorithms is developed and applied with the regularized total least squares minimization approach to estimate a set of the optimal regularization parameters and to retrieve a corresponding set of vertical Volume Emission Rate (VER) profiles. Furthermore, these algorithms take emissions of another origin and the Earth's shape into account. Considering not identified states of O2, the established photochemical models are adjusted resulting in two model modifications. Both model modifications are employed to retrieve the [O(3P)] time series on the basis of the VER time series in the MLT. The model input parameters vary in the atmosphere that motivated to propose these two model modifications and to employ available sources of the input parameters. One semi-empirical model, one general circulation model and the satellite-borne instrument SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) are employed as sources of the reference [O(3P)] and input parameters time series. The SABER instrument employed as a source of the input parameters is preferred according to the comparison of the retrieved and reference [O(3P)] time series. Studying the impact of the 11-year solar cycle on O(3P) in the MLT, an algorithm is developed and applied with the Levenberg-Marquardt algorithm to estimate the optimal fit parameters step-wise. The results of the O(3P) sensitivity analysis obtained with respect to the solar activity forcing at the 11 year and 27 day time scales and the lunar gravitational forcing agree with the reference model simulations. The hypothesis regarding vertical shifts between different of Meinel bands at least partly caused by the hydroxyl radical (OH*) quenching with O(3P) is confirmed experimentally. Based on the conclusion drawn in the first part of this thesis that the data sets’ self-consistency is high as for the averaged SABER and SCIAMACHY measurements, a comprehensive set of available data with a higher level of the data sets’ self-consistency is employed in the second part of this thesis. Multiple airglow emissions measured in situ during four campaigns are employed to propose the Multiple Airglow Chemistry (MAC) model. Processed emissions are the Herzberg I, Chamberlain, Atmospheric and Infrared Atmospheric band emissions of O2 and the green line emission of O. Considering all widely known and additionally complemented reactions, the MAC model is proposed to represent the oxygen airglow and the oxygen photochemistry in the MLT. The presented MAC model is based on the hypothesis of Slanger et al. (2004) stating that higher excited states of O2 are coupled with each other through vibronic de-excitation caused by collisions among molecules of this group of O2 states in the MLT. This hypothesis is modified excluding the singlet Herzberg state of O2 from the group of O2 states considered by Slanger et al. (2004). The MAC calculations are carried out sequentially starting with higher excited O2 states to provide the retrieved output concentrations of these O2 states as the input concentrations to the next calculation steps. The final step is only based on concentrations of all species, whereas each of the earlier steps is based on a corresponding VER profile besides of the input concentrations. The oxygen photochemistry in the MLT is represented by all species considered at the final step that makes it possible to adopt the MAC reactions in a general circulation model. Four modifications of the MAC model, i.e. including or excluding the triplet Herzberg states of O2 and including or excluding ozone and odd hydrogen (hydrogen, OH* and hydroperoxy radical), lead to negligible differences in the retrieved [O(3P)] profiles. Based on the MAC calculations verified and validated on the basis of the four rocket campaigns, one of the effective modifications of the MAC model (excluding the triplet Herzberg states of O2, ozone and odd hydrogen) is further reduced to the most effective modification. This implies that for the [O(3P)] retrieval only the O2 Atmospheric band emission, temperature and concentrations of molecular nitrogen (N2) and O2 are sufficient to apply. Calculations carried out by using the most effective modification of the MAC model are verified and validated on the basis of self-consistent in situ measurements obtained simultaneously. The MAC model enables identifying precursors of (1) the three lowest O2 valence states and (2) the second excited O state responsible for (1) the Atmospheric and Infrared Atmospheric band emissions of O2 and (2) the green line emission of O, respectively. Particularly, the singlet Herzberg state of O2 is identified as the major precursor of the second excited O state resulting in the green line emission. In focus of potential further research is an extension of the MAC model with vibrationally excited states of O2 and ionized species.

In this work, we theoretically investigate both aspects of charge-transferring atom-surface collisions: local-moment-type correlations and emission of secondary electrons from surfaces. Ideally, one chooses an approach that keeps as many electronic and lattice degrees of freedom at an ab-initio level as possible. In practice, however, this sophistication is hard to maintain. In this work, we do not aim to perform a description from first principles which could utilize density functional theory or quantum-chemical techniques. Instead, we keep only the most important degrees of freedom of the scattering process and use effective models for them. These are basically the Anderson-impurity model leading to time-dependent Anderson-Newns Hamiltonians and Gadzuk’s semiempirical approach to describe the projectile-target interaction from classical image shifts. In direct comparison with the description from first principles, the semiempirical approach offers a flexible basis for the modeling of a great variety of projectile-target combinations. The addition of further effective models to increase the general quality of the results is possible since the approach is very modular. The clear physical interpretation of each effective model, as well as the requirement for only a few and generally available parameters are further advantages of this approach. Rewritten in terms of Coleman’s pseudo-particle operators, the model is then numerically analyzed. This is done within a non-crossing approximation for the hybridization self-energies which are utilized by contour-ordered Green functions for each relevant electronic state of the projectile.

Matrix-product-state based methods, in particular the density-matrix renormalization group, are used to numerically investigate several one-dimensional systems, focusing on models with symmetry-protected topological phases that generalize the spin-1 Haldane chain. In the first part, ground state properties such as topological order parameters and the criticality at quantum phase transitions are studied.
The second part deals with dynamic properties of spin chains. Using time-dependent matrix-product-state calculations, the dynamic structure factor, and the transport properties of contacted spin chains are analyzed.

This thesis describes experiments with clusters stored in an electrostatic ion trap called Multi-reflection time-of-flight (MR-ToF) analyzer. These devices are established as mass separators and analyzers with high resolving powers and fast processing times. The objective was to characterize an experiment that utilizes such analyzer for cluster research, to this end a laser-ablation ion source was combined with an MR-ToF analyzer.
In the first part, an experiment scheme that combines two operating modes, namely in-trap lift operation and mirror operation, is presented and characterized for the present setup. For ion capture in-trap lift switching was employed and exit-side mirror switching for ejection with higher information content. Measurements were performed with small lead clusters to illustrate individual advantages of both techniques and the gain of combining them with focus on the ions’ ToF ejection window.
In the second part, a recently introduced method of ion separation by transversal ejection of unwanted species inside the trap was studied for the present setup. The ejection is performed by appropriate pulses of the potentials of deflector electrodes located in the trap. The various parameters affecting the selection effectivity and resolving power are illustrated with tin-cluster measurements, with resolving powers of up to several tens of thousands.
The third part presents the experiment in detail, with the construction of each component and measurements for its various performance parameters. Because the heart of the setup is the MR-ToF analyzer the characterization focuses on the trap. In addition, cluster ions were mass selected in the MR-ToF device and photodissociated. The charged fragments were stored and mass analyzed in a proof-of principle MS/MS experiment where both MS steps were performed in the MR-ToF operation mode.

This thesis describes mass measurements at ISOLTRAP/ISOLDE/CERN in the region of the neutron-rich calcium isotopes. For the less exotic and more abundantly produced isotopes 51Ca and 52Ca the Penning trap based ToF-ICR technique could be used to validate the available mass data and to improve their precision. For the isotopes 53Ca and 54Ca, a Multi-Reflection Time-of-Flight Mass Spectrometer (MR-ToF MS) was used to determine the mass of these exotic isotopes for the first time experimentally. This also represents the first time an MR-ToF MS was applied to derive the masses of previously unknown radioactive ions from the high precision time-of-flight data that can be gathered with the device. The mass data was then used to benchmark the strength of the N=32 neutron subshell closure and at the same time to compare to state-of-the-art shell-model calculations.
Furthermore, the capability of the MR-ToF device to deliver isobarically pure beams to a subsequent experiment was developed further and studied in detail. The new technique is based on the in-trap lift, which is normally used to in- and eject ions into and from the device. With this new selective ejection technique after separation of the ion ensemble in the MR-ToF trap, no external components are required.
Additionally, a new stabilization system for voltages supplies, based on a PI-algorithm, was developed and thoroughly tested. The stabilized voltage supply was then used to supply the most sensitive mirror voltage of the MR-ToF MS to significantly increase the short term and long-term mass resolving power of the apparatus.

In the present work high density helicon plasma discharges are created and characterized as a promising concept towards the realization of plasma wakefield accelerators to build up electric fields in the order of GV/m to accelerate electrons to energies in the TeV range with proton driving bunches. For such a concept plasma sources are needed that are able to maintain discharges with plasma densities of n_e = 7E20 m^-3 over long distances with a low variation in plasma density. Measurements at the PROMETHEUS-A device are performed for variable parameters, like magnetic induction, RF heating power and filling gas pressure. A CO2 laser interferometer, a laser induced fluorescence (LIF) diagnostic and a reaction rate model are combined to give a full picture. It is shown that in most cases the plasma density is centrally peaked with a high density region +- 5 mm from the center. The peak plasma density increases with increasing filling gas pressure, RF heating power and magnetic induction, limited by the number of neutral particles in low pressure discharges, by the transferred heating power and the increasing recombination and electron quenching rates of argon ions in high filling pressure cases. The increase in plasma density with increasing magnetic induction correlates to the direct proportionality in the helicon dispersion relation. For all investigated operational parameters the time evolution of the helicon discharge shows the same characteristics and is reliably reproducable inside the error bars. The electron temperature is determined by combining the collisional radiative model with line ratio measurements of two spontaneously emitted LIF lines. The low electron temperature regime of 1.2 eV < T_e < 1.4 eV and the electron temperature profiles are consistent with helicon wave heating via collisional power dissipation. The maximum plasma density of n_e = (6 +- 1)E20 m^-3 is measured at high RF power of P_RF = 24 kW, p_0 = 9 Pa filling gas pressure and a magnetic induction of B = 105 mT with a maximum electron temperature at 1.4 eV. At these operational parameters the plasma density peaking time and width are determined to be 270E-6 s and 50E-6 s, respectively. This shows that specific plasma density requirements for the use of a wakefield accelerator are reachable and the duration of the peak plasma density is more than sufficient for a relativistic particle to pass a 1 km long plasma cell. Additionally time-resolved LIF profile measurements for neutral and singly ionized argon were conducted to complement the previously evaluated measurements. The time resolution of the LIF diagnostic was chosen in a way to adequately represent the evolution of densities and to allow full profile measurements over one day. A resolution of 200E-6 s was chosen. The time-resolved neutral and ion metastable densities show hollow profiles with high densities at the edges over the first ms indicating higher ionization levels and increasing electron quenching rates. The metastable densities are highly determined by electron temperature, RF heating power and filling neutral gas pressure and do not reflect the neutral argon evolution. To investigate the influence of neutral depletion on the density evolution and maximum plasma density, the argon neutral and ion ground state densities are determined. Both time-resolved density profiles show a hollow profile with highest densities at the edges over a longer time interval of 3-4 ms. The penetration depths (ionization mean-free paths) indicate increased ionization of neutral argon while dissipating inwards, corresponding well to the theoretical value of lambda = 20 mm. This results in a depletion of neutrals in the center of the discharge, leading to a limitation and a fast decrease of plasma density after the neutrals are partially ionized. The shown refilling effect of neutral argon is too slow to have an important impact. At operation parameters for highest plasma density, the calculated ground states also show a fast increase in density at the end of the discharge after the RF-heating is switched off. This indicates recombination effects to these atomic states and higher ionization levels than ArII in the helicon discharge.

This dissertation focusses on the numerical modelling of resonant destabilization of Alfvén eigenmodes by fast ions in fusion plasmas. It especially addresses non-linear simulations of stellarator plasmas in which particle collisions are retained. It is shown that collisions are required for a realistic description of Alfvén waves in plasmas relevant to nuclear fusion.
We start by carefully verifying the implementation of the collision operators into the electromagnetic version of the gyro-kinetic delta-f particle-in-cell code EUTERPE. After these initial benchmarks are completed successfully, the code is in a position to be applied to realistic tokamak and stellarator scenarios.
Since every collision operator needs to fulfil conservation laws, a momentum-conserving version of the pitch-angle scattering operator is implemented. This is in particular important for neoclassical transport simulations aimed at computing flux-surface variations of the electrostatic potential in stellarators.
Using the simplified CKA-EUTERPE model (employing a fixed-mode-structure approximation), we perform non-linear simulations in tokamaks and stellarators. We show that the non-linear dynamics of fast-ion-driven Alfvén eigenmodes is significantly influenced by collisions. They have the potential to enhance the saturation level and to affect the frequency chirping of the modes.
It is thus concluded that collisions play an essential role in determining Alfvén-eigenmode-induced fast-ion transport - an important issue for future fusion devices. In order to address this issue the CKA-EUTERPE model is extended to evolve multiple modes at the same time. First results of this multi-mode version (which enhances the level of realism of the simulations) are shown in the Appendix of the thesis.

The goal of this thesis was to characterize the properties of tetramyristoyl cardiolipin (TMCL) and several environmental influences on it. This included investigating the pH and temperature dependency of TMCL as well as the influences of ROS on TMCL and exam-ining the lipid-protein interactions between TMCL and cytc. Furthermore, I extended the research to the analysis of binary mixtures composed of TMCL and dimyristoyl phosphati-dylcholine (DMPC). To this end, I investigated the samples with the aid of the Langmuir monolayer technique. This method allowed me to mimic interactions occurring at the membrane surface as it represents one membrane layer. The recording of π-A isotherms was also coupled with further other techniques like Brewster angle microscopy (BAM), Infrared Reflection-Absorption Spectroscopy (IRRAS), Grazing Incidence X-Ray Diffraction (GIXD) and Total Reflection X-Ray Fluorescence (TRXF) to enable a more comprehensive monolayer study. In addition, some systems were analyzed using Thin-layer Chromatography (TLC) and/or Differential Scanning Calorimetry (DSC) to be able to draw conclusions about sample composition or characteristic temperatures, respectively.

Optomechanical (om) systems are characterized by their nonlinear light-matter interaction. This is responsible for unique dynamic properties and allows the detection of a variety of classical and quantum mechanical phenomena on a microscopic as well as on a macroscopic scale. In this work we have studied the dynamic behavior of two laser-driven om systems, the single om cell ("cavity optomechanics / membrane-in-the-middle setup") and a two-dimensional hexagonal array of these cells ("om graphene"). The first case was motivated by the possibility to detect the transition from quantum mechanics to classical mechanics directly on the basis of the dynamic behavior. For this we focus on multistability effects of the optical and mechanical degrees of freedom, that are modeled by harmonic oscillators. Our description is based on the quantum optical master equation, which takes into account the environmental interaction assuming a vanishing temperature. As a consequence of decoherence, the dynamics occur near the semiclassical limit, i.e. it is characterized by quantum fluctuations. The quantum-to-classical transition is realized formally by rescaling the equations of motion. In the classical limit, quantum fluctuations disappear and the mean field equations were evaluated by analytical and numerical methods. We found that classical multistability is characterized by stationary signatures on the route to chaos, as well as by the coexistence of single-periodic orbits for the mechanical degree of freedom. The latter point was extensively evaluated by means of a self-consistent approach. For the dynamics in the quantum regime quantum fluctuations cannot be neglected. For this purpose, the master equation was solved by means of a numerical implementation of the Quantum State Diffusion (QSD) method. Based on Wigner and autocorrelation functions, we were able to show that quantum multistability is a dynamic effect: chaotic dynamics is suppressed and there is a time-dependent distribution of the phase space volume on classical simple-periodic orbits. The results can be interpreted within a semiclassical picture, which makes use of the single QSD quantum trajectory. Accordingly, the quantum-classical transition is explained as a time-scale effect, which is determined by tunneling probabilities in an effective mean-field potential. The subject of the second part of the work is the transport of low-energy Dirac quasiparticles in om graphene, propagating as light and sound waves. For this purpose, we investigated the scattering of a plane light wave by laser-induced photon-phonon coupling planar and circular barriers. The starting point is the om Dirac equation, which results from the continuum approximation of the Hamiltonian description of the two-dimensional array near the semiclassical limit. This work was motivated by the rich and interesting relativistic transport and tunneling phenomena found for electrons in graphene, which now appear in a new way. The reason is the presence of the new spin degree of freedom, which distinguishes the optical and mechanical excitations. In this spin space, the om interaction can be understood as a potential, which in our analysis consists of a time-independent and a time-dependent sinusoidal part. For the first case of a static barrier, the transport is elastic and is characterized by stationary scattering signatures. After solving the scattering problem via continuity conditions we were able to identify different scattering regimes depending on scattering parameters. In addition to relativistic phenomena such as Klein tunneling, simple parameter variation allows to use the barrier as a resonant light-sound interconverter and angle-dependent emitter. For the oscillating barrier, the transport is inelastic and is characterized by dynamic scattering signatures. To solve the time-periodic scattering problem, we have applied the Floquet theory for an effective two-level system. As a result of the barrier oscillation, photons and phonons can get and give away energy portions in the form of integer multiples of the oscillation frequency. The interference of short (classical) and long-wave (quantum) components leads to mixing of the scattering regimes. This allows to use the barrier as a time-periodic light-sound interconverter with interesting radiation characteristics. In addition, we have argued that the oscillating barrier provides the necessary energetic conditions for detecting zitterbewegung.

Ion thrusters are Electric Propulsion systems used for satellites and space missions. Within
this work, the High Efficient Multistage Plasma Thruster (HEMP-T), patented by the
THALES group, is investigated. It relies on plasma production by magnetised electrons.
Since the confined plasma in the thruster channel is non-Maxwellian, the near-field plume
plasma is as well. Therefore, the Particle-In-Cell method combined with a Monte-Carlo
Collision model (PIC-MCC) is used to model both regions. In order to increase the sim-
ulated near-field plume region, a non-equidistant grid is utilised, motivated by the lower
plasma density in the plume. To minimise artificial self-forces at grid points bordered by
cells of different size a modified method for the electric field calculation was developed in
this thesis. In order to investigate the outer plume region, where electric field and collisions
are negligible, a ray-tracing Monte-Carlo model is used. With these simulation methods,
two main questions are addressed in this work.
What are the basic mechanisms for plasma confinement, plasma-wall-interaction
and thrust generation?
For the HEMP-T the plasma is confined by magnetic fields in the thruster channel, generated
by cylindrical permanent magnets with opposite polarity. Due to different Hall parameters,
electrons are magnetised, while ions are not. Therefore, the dominating electron transport
is parallel to the magnetic field lines. In the narrow cusp regions, the magnetic mirror effect
reduces the electron flux towards the wall and confines the electrons like in a magnetic
bottle. At the anode, propellant gas streams into the thruster channel, which gets ionised
by the electrons creating the plasma. As a result of the electron oscillation between the two
cusp regions, ionisation of the propellant gas is efficient.
The magnetic field configuration of the HEMP-T also influences the plasma potential inside
the thruster channel. Close to the symmetry axis, the mainly axial magnetic field results in
a flat potential. At the inner wall, the field configuration reduces the plasma wall interaction
to only the narrow cusp regions. Here, the floating potential of the dielectric channel wall
and its plasma sheath result in a rather low radial potential drop compared to the applied
anode potential. As a result, the electric potential is rather flat and impinging ions at the
thruster channel wall have energies below the sputter threshold energy of the wall material.
Therefore, no sputtering appears at the dielectric wall. At the thruster exit the confinement
by the magnetic field is weakened and the potential drops with nearly the full anode voltage.
The resulting electric field accelerates the generated ions into the plume and generate the
thrust, but they are also able to sputter surfaces. During terrestrial testing, sputteringat vacuum vessel walls leads to the production of impurities. The amount of back-flux
towards the channel exit is determined by the sputter yield of the vacuum chamber wall. A
large distance between thruster exit and vessel wall reduces the back-flux and smooths the
pattern of deposition inside the thruster channel. Dependent on their material, the evolving
deposited layers can get conductive, modify by this the potential distribution and reduce
the thrust.
For the HEMP-T, ions are mainly generated at high potential close to the applied anode
potential. Therefore, the accelerated ions producing the thrust gain the maximum energy
as observed in experiment. Ions emitted from the thruster into different angles in the
plume contribute mainly to the ion current at angles between 30 ◦ and 90 ◦ . They mainly
originate from ionisation at the thruster exit. The resulting angular distribution of the
ejected ion current is close to the one of the experiment, slightly shifted by about ten
degrees to higher emission angles. In front of the thruster exit, electrons are trapped by
electrostatics forces. This enhanced density allows ionisation and an additional electron
density structure establishes.
What are possible physics based ideas for optimisation of an ion thruster?
An optimised thruster should have a high ionisation rate inside the thruster channel, low
erosion and an ion angular distribution with small contributions at high angles for min-
imised thruster satellite interactions. In experiments, the HEMP-T satisfies already quite
nicely these requests. In the simulations, low erosion inside the thruster channel and angular
ion distributions close to the experimental data are demonstrated. However, the ionisation
efficiency is lower and radial ion losses are larger than in experiment. A possible explanation
of these differences is an underestimated transport perpendicular to the magnetic field lines,
well known for magnetised plasmas.
A successful example for an optimisation using numerical simulations is the reduction of
back-flux of sputtered impurities during terrestrial experiments by an improved set-up of
the vacuum vessel. The implementation of baffles reduces the back-flux towards the thruster
exit and therefore deposition inside the channel. These improvements were successfully im-
plemented in the experiment and showed a reduction of artefacts during long time measure-
ments. This leads to a stable performance, as it is expected in space.

Manipulating and utilizing plasmas becomes a more and more important task in various research fields of physics and in industrial developments. Especially in nowadays spacerelevant applications there are different ideas to modify plasmas concerning particular tasks.
One major point of interest is the ability to influence plasmas using magnetic fields. To study the underlying physical effects that were achieved by these magnetic fields for both scenarios Particle-in-Cell simulations were done. Two examples are discussed in this thesis.
The first example originates from an experiment performed by the European Space Agency ESA in collaboration with the German Space Agency DLR. To verify the possibility of heat-flux reduction by magnetic fields onto the thermal protection system of a space vehicle a simplified experiment on earth was developed. Most of the heat that is created during re-entry comes from compression of the air ahead of the hypersonic vehicle, as a result of the basic thermodynamic relation between temperature and pressure. The shock front, which builds up in front of the vehicle deflects most of the heat and prohibits the surface of the space vehicle from direct contact with the maximum flux. State of the art spacecrafts use highly developed materials like ceramics to handle the enormous heat. An attractive approach to reduce costs is to use magnetic fields for heat-flux reduction. This would allow the use of cheaper materials and thus reduce costs for the whole space mission. A partially-ionized Argon beam was used to create a certain heat-flux onto a target. The main finding of the experimental campaign was a large mitigation of heat-flux by applying a dipole-like magnetic field. The Particle-in-Cell method was able to reproduce experimental observations like the heat-flux reduction. An additionally implemented optical diagnostics module allowed to confirm the results of the spectroscopy done during the experiment. The underlying effect that is responsible for the heat-flux reduction was identified as a coupling between the modified plasma and the dominating neutral flux component. The plasma, that is guided towards the target, act as a shield in front of the target surface for arriving neutrals. These neutrals are slowed down by charge-exchange collisions. Furthermore the magnetic field induces an increased turbulent transport that is also needed to reach a reduction in heat-ux. The turbulent transport was also obtained by three-dimensional Direct Simulation Monte Carlo simulations. Unfortunately, such source driven turbulence can not be expected in space, so that a heat flux reduction in real space applications is questionable. Nevertheless, other effects like the induced turbulence by the rotating vehicle can compensate the missing source driven effect.
The second scenario in which a magnetic field is used to modify the heat flux of a plasma is the operation of the pulsed cathodic arc thruster. The same Particle-in-Cell code was used to simulate a typical pulse of this newly developed thruster of Neumann Space Pty Ltd. The typical behavior of the thruster could be reproduced numerically. The thrust is mainly produced by fast electrons. These electrons are accelerated by electric fields as a result of a plasma-beam instability. This plasma-beam instability was verified by a phase space diagnostics for the electrons. To demonstrate the influence of the magnetic field a simulation of the cathodic arc thruster without magnetic field and one with magnetic field were compared. It was shown that the use of a magnetic field leads to a ten times larger thrust by directing the heat ux. The resulting narrow plume is an additional Advantage of the particle guiding magnetic field. This narrowness of the plume reduces the danger of interaction with other components of the space vehicle.
Both scenarios demonstrate the different capabilities for electromagnetic fields to manipulate plasmas and especially the corresponding heat-flux with respect to certain tasks. The possibilities range from reducing the heat-flux onto a target to maximizing the thrust by directing the heat-ux. This thesis demonstrates that simulations are a great tool to support experiments and to deliver an improved physics understanding. They help to identify the basic physics principles in the different systems, because they can deliver information not accessible to experiments.
In particular, a better understanding of the influence of electromagnetic fields on the heat-flux distribution in space-relevant applications was obtained. This can be the basis for further simulation-guided optimization, e.g. for the design of more effective cathodic arc thrusters. Here, the goal is to minimize costs for prototypes by replacing the hardware by virtual prototypes in the simulations. This allows to test basic design ideas in advance and get more highly-optimized designs at a fraction of time and costs.

This work study a monolayer of branched poly(ethyleneimine (PEI) adsorbed onto oppositely charged surfaces with iron chelates or iron ions in the absorption solution. The conformation of adsorbed PEI is explored in the dependence of the composition of the adsorption solution by measuring the surface forces using atomic force microscopy (AFM) with the colloidal probe (CP) at different ionic strengths (INaCl) in surrounding aqueous solution. The surface coverage of these layers is investigated using X-ray reflectivity.
PEI solutions show different pH values with iron chelates (pH = 3), iron ions (pH = 4.67) or pure water (pH = 9.3) at room temperature. Low surface coverage of PEI at pH = 3 adjusted by monovalent ions was also observed. However, adsorbing PEI with iron ions or iron chelates and washing with pure water shifts the pH, leading to an adsorbed PEI layer with high coverage. In our observation, the influence of iron ions and iron chelates on the surface coverage of PEI film is stronger than the pH effect. PEI adsorbed from a pure water solution shows flat conformation. Surface force measurements with CP show that PEI adsorbed from solutions containing iron chelates or iron ions cause almost identical steric forces. The thickness of the brush L is determined as a function of the ionic INaCl in the measuring solution. It scales as a polyelectrolyte brush.
The maximum number density of gold nanoparticles (AuNPs) adsorbed onto the PEI brushes was identical and larger than on flatly adsorbed PEI. On the PEI layer with the larger surface coverage, the AuNPs aggregate; on the PEI layer with the lower surface coverage they do not aggregate. Taken together, these results contribute to understanding the mechanisms determining surface coverage and conformation of PEI and demonstrate the possibility of controlling surface properties, which is highly desirable for potential future applications.
In this thesis, we also investigate the top layer (PSS and PDADMA) of polyelectrolyte multilayer (PEM) films. PEM films were prepared by sequential adsorption of oppositely charged PEs on solid substrates. PEM films consist of polydiallyldimethylammonium (PDADMA) as polycation and the polystyrene sulfonate (PSS) as polyanion. PDADMA has a smaller linear charge density than PSS. For this system, two different growth regimes are known: parabolic and linear. I studied the top layer (PSS and PDADMA) conformation of PEM films and how the structure of this top layer is affected by increasing the number of PDADMA/PSS layer pairs N and the addition of salt to the surrounding solution.
The INaCl was changed during the force-distance measurements. PSS terminated films always show electrostatic forces at INaCl < 0.1 M and flat conformation. The surface charge density is always negative at INaCl < 0.1 M. The surface charge of the PSS top layer starts to turn from negative to positive at N ≥ 14. At N between 13 and 15, adsorbed PSS cannot compensate all the excess PDADMA charge. This leads to an accumulation of the positive extrinsic sites within the PSS terminated film beyond a specific N. At INaCl ≈ 0.1 M, an exponential decaying force was measured. This is an indication of unusual long-ranged hydration force (decay length λ-1 ≈ 0.2-0.5 nm), and PSS terminated film shows zwitterionic or neutral surface. At INaCl > 0.1 M, a non-electrostatic action occurs and the PSS terminated film reswells in solution.
PDADMA terminated surface consisting of few layers show a flat conformation and the electrostatic forces were measured. For N ≥ 9 and INaCl ≤ 0.1 M, steric forces were measured. The force-distance profiles are well-explained by Alexander and de Gennes theory. PDADMA chains show a maximum L that is around 40-45 % of the contour length. For INaCl ≈ 0.1 M, and N > 9, a flat, neutral or zwitterionic surface is found (λ-1 ≈ 0.3-0.9 nm). For N = 9 and INaCl > 0.1 M, a strong screening of electrostatic interaction and attractive forces are observed. For N > 9 and INaCl > 0.1 M, the ion adsorption into the PE chains leads to an increase in the monomer size and as a result, the L increases and PDADMA brushes reswell again into the solution.
These data show that by varying N and INaCl, different surface forces can be obtained: Electrostatic forces (flat chains) both positive and negative, steric forces (brush), hydration force (flat, neutral or zwitterionic surface), and effects not yet explained (reswelling brush).

In this thesis, size-sensitive phenomena of three-dimensional dust crystals emerged in a low temperature plasma are presented. Depending on the number of particles in the system phase transitions, collective vortex motions and large-scaled expansions can be observed. To investigate these fascinating effects an advanced experimental setup as well as new evaluation methods have been developed. This thesis will present these new techniques and the gained insights.

Lead-cluster investigations
(2017)

In this thesis, investigations on lead clusters stored in a Penning trap are presented. The measurements are performed at the ClusterTrap setup at the Institute of Physics of the University of Greifswald. A Penning trap with a superconducting magnet (B=12 Tesla) makes up the central part of the experiment. In this trap, singly positively or negatively charged lead clusters (a group of lead atoms) are stored, their amplitudes of motion are cooled, and a specific cluster size is selected. Thus, clusters of only a single size are prepared for experimental investigation. After interactions with electrons and/or photons, the trap content is extracted and analyzed by time-of-flight mass spectrometry.
In the first experiment, the size-selected clusters are excited by a frequency-doubled Nd:YAG laser, which leads to fragmentation processes. The preferred fragmentation pathway, which is observed to be break-off of a seven-atom neutral cluster is unusual for metal clusters, which typically evaporate monomers. Furthermore, the already known magic cluster sizes are observed.
In a subsequent experiment, positively charged lead clusters with 31 atoms are irradiated with laser light and fragmentation processes are time resolved investigated. The assumption that lead clusters fragment by break-off of neutral heptamers is confirmed.
In the following experiment, an electron beam is guided through the Penning trap to ionize pulsed-in argon atoms. While the positive argon ions leave the trap, the secondary electrons are trapped together with the selected lead clusters. This allows the electrons to attach to the singly charged lead clusters, which leads to multiply negatively charged lead clusters. The relative abundance of multiply-charged clusters is measured with respect to the cluster size, from which the appearance sizes of di- and trianions can be calculated. In addition to the attachment of electrons, fragmentation products similar to those of the photoexcitation measurements are observed. Furthermore, the cluster sizes 10 and 12 are observed regardless of the investigated precursor size, together with clusters of the precursor size reduced by 10 and 12. This is a first hint for a fission process of doubly negatively charged lead clusters into two singly charged products. In a following measurement, doubly charged lead clusters are produced and photoexcited. The observed abundance spectra confirm this assumption.

This work examines the influence of monovalent and divalent cations on tetramyristoyl cardiolipin (TMCL) monolayers. A lipid monolayer can undergo an ordering transition of the lipid alkyl chains from a disordered fluid phase (liquid-expanded (LE)) to an ordered gel phase (liquid-condensed (LC)). Compression of the lipid monolayer in a Pockels-Langmuir trough was monitored with a Wilhelmy plate tensiometer, yielding the surface pressure π in dependence of the area a molecule can occupy on average A, as a π-A-isotherm. The onset of the first order LE/LC phase transition is marked by an abrupt change in the isotherm at surface pressure πc.
These associated lipid membrane changes were characterized by variation of the compression speed, kind and concentration of the monovalent and divalent salt, pH, and temperature. The CL monolayer phase transition was found to depend on the compression speed, yielding only a small variation in the compression isotherms.
For monovalent cations on the cardiolipin monolayer, the dependence on salt concentration of the lipid liquid gel phase transition surface pressure πc was determined and a non-monotonic behavior was found, with a maximum in πc for a salt concentration of 0.1 mol/l. The maximum in πc can be shifted with pH (e.g. pH = 4.2). This behavior extended to potassium, sodium and cesium cations in the subphase. No ion specific effects were observed, which pointed to the prevalence of electrostatic interactions in the system.
Different divalent salt subphases, of either magnesium, calcium, strontium, manganese, iron or zinc salts, with fixed sodium chloride concentration of 0.15 mol/l at pH of 5.8 and 25 °C were investigated. πc decreases upon addition of divalent salts to the subphase. This points to increased screening and binding effects. Strongest binding effects were observed for calcium and manganese cations.
The electrostatic interactions of the system were modeled with a mean-field theory: Grahame’s equation, and a simple law of mass action. CL is modeled at half its molecular area and half its charge, with a proton dissociation constant of the phosphate group Ka,intrinsic(PO4) = 0.1 mol/l. The agreement with the experiment was satisfactory.
A linear dependence of πc on the temperature was found for cardiolipin monolayers on all subphases. The isothermal area compressibility modulus KA is calculated from selected isotherms. It was found that the flexibility of the monolayer decreases with temperature and the area per molecule for the cardiolipin fluid phase.
The compression speed, monovalent salt concentration, pH, and selected divalent cations were investigated with the BAM. For all a sigmoidal growth of xgel with compression was observed. For high salt concentrations non-circular and dendritic domains were observed.
A simple model for the nucleation process was introduced, yielding an estimate of 20 nm for the critical domain radius, which is below the resolution of the BAM, but a common length scale in biological systems.