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Graphene is a strictly two-dimensional honeycomb lattice of carbon atoms whose low-energy charge-carrier dynamics obey the massless pseudospin-1/2 Dirac-Weyl equation (or chiral Weyl equation) where the chiral centers (or valleys) are the corners K and K‘ of the Brillouin zone. The linear spectrum near the Dirac nodal points lends graphene its exotic and ultra-relativistic properties. However, condensed matter systems can possess fermionic excitations with linear dispersions that have no analog in high-energy physics since the crystal space group - instead of the Poincare group - constrains the energy dispersions. Perhaps the first example in this regard is the T_3 lattice (Dice Gitter), a honeycomb-like lattice with an extra atom placed at the center of each hexagon and coupled to only one of the sublattices. The spectrum features a strictly flat band that crosses the two conical intersections of the Dirac cones at K and K' inherited from graphene. The enlarged pseudospin-1 Dirac-Weyl equation describes the low-energy dynamics. By rescaling the transfer amplitude of the additional atoms in the T_3 lattice with a parameter 0<α<1, the resulting α-T_3 lattice continously interpolates between graphene and the T_3 lattice. In this work, we explore the behavior of generalized Dirac-Weyl quasiparticles in external magnetic and valley-dependent pseudoelectromagnetic fields induced by out-of-plane strain. First, we studied Dirac-Weyl quasiparticles in external fields confined to circular quantum dots by generalizing the infinite-mass boundary condition to the α-T_3 lattices. We verified the analytically derived valley-anisotropic eigenstates of the quantum dot by numerically solving the tight-binding lattice-model in closed (isolated) and open (contacted) systems. Second, we considered strain fields in the α-T_3 lattices to modify the low-energy transport properties by an effective pseudo-gauge field with opposite signs at the K and K‘ valley. In particular, we showed that the inhomogeneous pseudomagnetic field generated by Gaussian out-of-plane strain at the center of a four-terminal Hall bar setup acts as a valley filter. Most interestingly, the valley polarization is most dominant when incoming electrons are excited to pseudo-Landau level subbands. These bands are linked to different iso-field orbits encircling the lobes of the pseudomagnetic field. Addittionaly, any intermediate α breaks the inversion symmetry of the α-T_3 lattice and thus splits the pseudo-Landau levels into sublattice-polarized bands. Third, we equipped the out-of-plane strain with a time-periodic drive to induce a valley-dependent pseudoelectric field perpendicular to the pseudomagnetic field. We assessed the steady-state transport properties and found – besides the static regime for small energies – two α-dependent valley-filtering regimes due to the periodic drive. Firstly, we found an additional valley-polarization plateau at the Floquet-zone boundary between the central and first Floquet copy that also displayed a “flower”-like pattern in the local density of states. Secondly, we detected a series of transmission gaps at the center of every Floquet sideband 2mΩ related to the Floquet coupling of the flat band with the central Floquet copy. Under certain strain parameters, a novel valley-filtering regime appears near the transmission gaps where the incoming K electrons are focused through the bump by the pseudoelectric field, instead of encircling the lobes of the pseudomagnetic field. A stability analysis demonstrated that the polarization regimes are tunable by the driving frequency. Lastly, we demonstrated that the flat band in the Haldane-dice lattice modified by a uniaxial strain along the zigzag orientation remains singular at all band crossings where the model undergoes a topological phase transition between C=+-2 and C=0. To show this, we computed the compact localized eigenstates and the quantum distance of the Bloch wave function around the band-touching points. We derived the resulting non-contractible loop states and an extended state whose components are tunabe by the system parameters.

Ion trajectories have been simulated for an assembly of a linear quadrupole ion-filter and a linear Paul trap with additional pin electrodes for MS SPIDOC, a project in preparation for the study of biomolecules by single-particle imaging with X-ray pulses. The ion-optical components are based on digital RF guiding and trapping fields. In order to carefully handle biomolecules over a wide mass-over-charge range, the module presented consists of separate components for filtering and accumulation/trapping in order to select the ions of interest and to convert the beam from a continuous ion source to ion bunches, respectively, as required for the experiments downstream. The present analysis focuses on the transmission efficiency and mass resolving power of the filter, as well as the buffer-gas-pressure-dependent ion capture and thermalization in the trap for the example of a mass-to-charge ratio equivalent to hemoglobin 15+ ions. The resulting optimized ion bunch delivered by the assembly is characterized.

Polyelektrolyt-Multischichtfilme (PEMs) werden durch schichtweise (eng. Layer by Layer, LbL) sequentielle Ablagerung von entgegengesetzt geladenen Polyelektrolyten auf einer geladenen Oberfläche hergestellt. Die LbL Methode kann auf verschiedene Weise zur Herstellung von PEM eingesetzt werden, z.B. durch Tauchen, Rotation, Sprühen oder Beschichten mit elektromagnetischen und fluidischen Methoden. In allen Artikeln dieser Dissertation wurde die Tauchmethode verwendet. Durch zyklische Wiederholung der Abscheidungsschritte kann die Dicke der PEM leicht gesteuert werden. Die Oberflächen und Grenzflächen des Films können mit der LbL Technik auch durch die elektrostatische Wechselwirkung zwischen positiv und negativ geladenen Polyelektrolyten modifiziert werden. Auf diese Weise lassen sich einige Eigenschaften des Films optimieren, beispielsweise Oberflächenadhäsion und Biokompatibilität, z. B. in der Gewebezüchtung oder es kann eine Monoschicht als Barriere an der Grenzfläche des Films adsorbiert werden, um die Diffusion von Molekülen im Film zu begrenzen z.B. bei Aufnahme oder Freisetzen von Medikamenten. Daher wurde die Rolle einiger Faktoren, wie die molare Masse der Polyelektrolyte und das Vorhandensein von Salzionen in der Präparationslösung auf die interne Struktur sowie die Oberfläche der PEMs untersucht. Für alle Untersuchungen dieser Dissertation wurde das häufig verwendete Modell-System aus dem positiv geladenen Polyelektrolyten Polydimethyldiallylammonium (PDADMA), und dem negativ geladenen Polyelektrolyten Polystyrolsulfonat (PSS), verwendet. Die Dicke der Filme wurde mit Röntgenreflektometrie, Ellipsometrie, UV-Vis-NIR-Spektrometrie bestimmt die interne Struktur mit Neutronenreflektometrie und die Oberflächentopografie mit Rasterkraftmikroskopie (eng. AFM) und Rasterelektronenmikroskopie (eng. SEM). In Artikel 1 wurde mit Hilfe der Neutronenreflektometrie die Struktur des Filmes und die Diffusion des Polyanions PSS (DPSS) senkrecht zur PEM Oberfläche untersucht. Variiert wurde die molare Masse des Polykations PDADMA und die Salzkonzentration der Präparationslösung. PEMs wurden aus drei verschiedenen NaCl-Konzentrationen in der Abscheidelösung hergestellt: 10 mmol/L, 100 mmol/L und 200 mmol/L. Die Salzkonzentration in der Polyelektrolytlösung bestimmt die Konformation der Polyelektrolyte während der Adsorption. Die Ketten werden weniger flach adsorbiert, wenn mehr Salzionen in der Adsorptionslösung vorhanden sind und die Filme werden dicker. Die Diffusion nahm mit zunehmender molarer Masse von PDADMA in Filmen, die aus 10 mmol/L, 100 mmol/L und 200 mmol/L hergestellt wurden, um mindestens drei Größenordnungen ab, denn die Zunahme der Kettenlänge, erhöht den Vernetzungsgrad im Film. Dabei zeigten Filme aus 10 mmol/L (NaCl) mit einer niedrigen molaren Masse von PDADMA die größte Diffusion (DPSS = 4.9 × 10−20 m2/s). Der Diffusionskoeffizient DPSS als Funktion des Polymerisationsgrades folgt zwei Potenzgesetzen mit einem Übergang bei einem Polymerisationsgrad von 288. Bei kürzeren Ketten stimmt der Exponent des Potenzgesetzes gut mit dem Modell der Sticky Reptation überein. Bei längeren Ketten war der Exponent viel größer, was vermuten lässt, dass die PSS-Ketten in einem zunehmend komplexen Polymernetzwerk gefangen sind. Wir verstehen den Übergang als Verschränkungsgrenze für das untersuchte System. Bei PEMs, die aus 100 mmol/L hergestellt wurden, konnte kein Potenzgesetz festgestellt werden. DPSS nahm sprunghaft um drei Größenordnungen ab, wenn die molare Masse von PDADMA von 45 kDa auf 72 kDa erhöht wurde. In Artikel 2 wurden die Oberfläche von PEMs aus Polyelektrolyten unterschiedlicher molarer Massen untersucht. Die Oberflächenrauhigkeit und die Dicke des Films wurden mit Röntgenreflektometrie und Ellipsometrie bestimmt. Die Oberflächentopografie wurde mit AFM und SEM aufgenommen. Alle PEMs wurden aus PE-Lösungen mit 0,1 mol/L NaCl hergestellt. Die Oberfläche der PEM, präpariert aus langem PSS und kurzem PDADMA oder langem PSS und langem PDADMA, war immer flach. Bei einer Filmzusammensetzung aus langen Polykationen (Mw (PDADMAlang) = 322 kDa) und kurzen PSS Molekülen (Mw (PSSkurz) = 10,7 kDa) wurden drei Wachstumsregime identifiziert: exponentiell, parabolisch und linear. Im exponentiellen Wachstumsregime bildet sich nach etwa sieben Beschichtungsschritten von PDADMA/PSS (eng. bilayers, bl) eine granulare Oberflächenstruktur aus mit einer Oberflächenrauigkeit von 1,6 nm und einer lateralen Periodizität von 70 nm. Mit zunehmender Schichtzahl nimmt die Oberflächenrauhigkeit sowie die laterale Periodizität zu. Im parabolischen Wachstumsbereich aggregieren die Strukturen zu Säulen, mit einer Oberflächenrauigkeit bis zu 23 nm und einer lateralen Periodizität bis zu 210 nm. Im linearen Wachstumsregime sind die säulenförmigen Domänen vollständig ausgebildet und die Oberflächenstruktur ändert sich nicht mehr. Diese Strukturen wurden schon während der Präparation, bereits vor dem Trocknen beobachtet. Dies zeigt, dass sich die Strukturen während der Abscheidung von PDADMA/PSS bilden. Bei Beobachtungen im Vakuum (SEM) war im linearen Bereich die Säulenstruktur bei der PDADMA terminierten PEM ausgeprägter als bei der PSS terminierten. Diese Strukturen bilden sich nur im Film mit anfänglichem exponentiellem Wachstum, d.h. wenn kurzen Ketten durch den ganzen Film diffundieren können. Das legt nahe, dass es für die Strukturbildung nicht ausreicht, dass der Polyelektrolyt kurz ist, sondern dass es auch beweglich sein muss. Um dies näher zu untersuchen wurde in Manuskript 1 die molare Masse des PSS variiert. Es wurden PEMs aus langem 322 kDa PDADMA und kurzem 6,5 kDa und 3,9 kDa PSS hergestellt und mit den Messungen von PEMs aus 10,7 kDa PSS verglichen. Die Verkürzung von PSS hat subtile Auswirkungen auf den Filmaufbau und die Selbststrukturierung. Für PEM aus PSS mit einer molaren Masse von 6,5 kDa konnten nur zwei Wachstumsregime ermittelt werden: ein exponentielles und ein lineares Wachstumsregime. Der Übergang vom exponentiellen zum linearen Wachstum erfolgte bei 28 Doppelschichten. Bei PEMs, die aus 3,9 kDa PSS hergestellt wurden, wurde bis zu 29 bl nur ein exponentielles Wachstum beobachtet. Dies zeigt, dass eine Verringerung der molaren Masse von PSS das exponentielle Wachstum auf eine größere Anzahl von abgeschiedenen Doppelschichten ausdehnt. Dies ist auf die zunehmende PSS-Diffusion zurückzuführen. In allen Filmen wurden Selbststrukturierungen beobachtet. Der Abstand und die Höhe der säulenartigen Domänen nehmen mit jeder abgeschiedenen PDADMA/PSS-Doppelschicht deutlich zu. Der durchschnittliche Domänenabstand ändert sich weniger und korreliert mit den vertikalen Wachstumsregimen. Der Domänenabstand schwankt zwischen 70 nm und 750 nm. Die größten lateralen Abstände und ein längeres exponentielles Wachstumsregime wurden mit dem kürzesten PSS (3,9 kDa) erreicht, was auf die hohe Mobilität des PSS zurückgeführt wird. Die Domänenhöhe ist immer kleiner als der Domänenabstand. Wenn die PEM mit PDADMA terminiert ist, sind die Oberflächenrauhigkeit und der durchschnittliche Abstand größer als bei PSS terminierten Filme in Wasser und nach dem Trocknen. Darüber hinaus wurden zwischen den Domänen Filamente beobachtet. Die Filamente bestehen aus PDADMA/PSS-Komplexen. Eine mögliche Vermutung ist, dass diese Komplexe zwischen den Domänen diffundieren und ihren Abstand anpassen. Die Oberflächenstruktur des Films aus PSS 10,7 kDa zeigt eine symmetrische gaußförmige Höhenverteilung in allen drei Wachstumsregimen von 5 bis 40 bl. Für die kurze PSS war eine solche Verteilung nur bis 15 bl (6,5 kDa) bzw. 20 bl (3,9 kDa) zu beobachten. Danach wurde für 6,5 kDa schiefe Verteilung mit Ausläufern zu größeren Höhen beobachtet. 3,9 kDa PSS zeigte dann sogar eine bimodale Höhenverteilung. Die lineare Ladungsdichte von PDADMA ist etwa halb so groß wie die von PSS. Folglich adsorbiert PDADMA in einer bürstenartigen Konformation. Wenn die oberste Schicht PDADMA ist, dann ist das PDADMA-Molekül nicht fest an die Oberfläche gebunden. Daher ist die durch die Oberflächenspannung erzeugte Kraft für PDADMA groß genug, um zu einer Veränderung der Oberflächenmorphologie und folglich zu einer kleineren Gesamtoberfläche zu führen.Außerdem sind die Domänen in 1 M NaCl-Lösung stabil, schrumpfen aber in 2 M NaCl enorm, während ihr Abstand leicht zunimmt. Diese Untersuchungen zeigten, dass die Mobilität des Polyelektrolyten PSS die Voraussetzung für den Aufbau einer strukturierten Oberfläche in einem PEM-System aus PDADMA/PSS ist. Diese Ergebnisse zeigten auch, dass die Verkürzung der Kette der PSS Moleküle die Herstellung von Filmen erleichtert, deren Dicke und Selbststrukturierung je nach dem gewünschten Zweck angepasst werden kann. Solche Filme können in der Medizin und Biologie als geeignetes Substrat zur Optimierung der Adsorption von Zellen und anderen Molekülen oder als Nanofilter effektiv eingesetzt werden. In dieser Dissertation konnte ich zeigen, wie die Verkürzung der Kette der PSS-Moleküle zur Bildung einer lateralen selbststrukturierten Oberfläche führt und wie die zunehmende Mobilität der PSS-Moleküle die Oberflächenmorphologie signifikant beeinflusst.

In this work, 2-dimensional measurements in the THz frequency range with self-made spintronic THz emitters were presented. The STE were used to optimize the spatial resolution and determine the magnetization in geometric shapes. At the beginning, various combinations of FM and NM layers were produced and measured to achieve an optimal composition of the STE. The layer thickness of the ferromagnetic CoFeB layer and the nonmagnetic PT layer was also varied. The investigations have shown that a layer combination of 2 nm thick CoFeB and 2 nm thick Pt, applied to a fused silica glass substrate and covered with a 300 nm thick SiO2 layer, emits the highest THz amplitude. Based on these, a structured sample, consisting of an STE and an additional layer system of 5 nm Cr and 100 nm Au, was produced. Further, three wedge-shaped structures were removed from the gold layer by an etching process so that the THz radiation generated by the STE can pass through these areas. This enables the optimization of the resolution of the system. For this purpose, the sample was moved perpendicular to the laser beam by two stepping motors with a step size of 5 μm and imaged 2-dimensionally. By reducing the step size to 0.2 μm, the beam diameter could be measured at the edge of the structure using the knife-edge method. Based on this measurement, the resolution of the system could be determined as 5.1 ± 0.5 μm at 0.5 THz, 4.9 ± 0.4 μm at 1 THz, and 5.0 ± 0.5 μm at 1.5 THz. These results are confirmed by simulations considering the propagation of THz wave packets through the SiO2. The expansion of the FWHM of the waves, passing through the 300 nm thick layer, is about 1%. Only a SiO2 layer with a thickness in the μm range occurs an expansion of around 10%. This shows that it is possible to perform 2-dimensional THz spectroscopy with a resolution in the dimension of the exciting laser beam by using near-field optics. Afterward, the achieved spatial resolution was used to investigate the influence of external magnetic fields on the STE and the emitted THz radiation. By implementing a pair of coils above the sample, an external magnetic field could be applied parallel to the pattern. The used sample was designed in such a way that only certain geometric areas on the fused silica glass substrate were coated with an STE so that THz radiation is emitted only in those areas. The 2-dimensional images show the geometric structures for f = 1.0 THz and f = 1.5 THz clearly. By applying a permanent, positive magnetic field (+M), a positive course of the THz amplitude can be seen. A rotation of the magnetic field by 180° (-M) leads to a reversal of the orientation of the emitted THz radiation, whereby the magnetic field does not influence the corresponding frequency spectrum. By using minor loops, the sample was demagnetized by the constant reduction of the magnetic field strength with alternating magnetic field direction. The 2-dimensional representation of the pattern with a step size of 10 μm shows that the sample was demagnetized since both, positively and negatively magnetized structures, could be imaged. In addition, in the 2nd row from the top, a completely demagnetized circle and a rectangle with a division into two domains can be seen. These structures have both positive and negative magnetized areas, which are separated by a domain wall. To investigate this in more detail a 2-dimensional measurement of the divided regions was made with a step size of 2.5 μm. These images confirm the division of the structures into positive and negative domains, separated by a domain wall, which was verified by Kerr-microscope measurements. Both data show a similar course of the domains and the domain wall. However, to be able to examine the domain wall more precisely using 2-dimensional THz spectroscopy, the resolution of the system must be improved to a range of a few nm, because the expected domain wall width is between 𝑙𝑊 = 12.56 nm and 𝑙𝑊 = 125.6 nm. The improved resolution would make it possible to image foreign objects, such as microplastics in biological cells or tissue. For this purpose, different plastics, such as polypropylene, polyethylene, and polystyrene, were investigated in the THz frequency range up to 4 THz. While no specific absorption could be determined for PP, characteristic absorption peaks were found for PE and PS. The energy of the photons with a frequency of about 2.2 THz excites lattice vibrations in the PE. Therefore, this frequency is specifically absorbed, and the intensity in the transmission spectrum is lower than for other frequencies. PS absorbs especially THz radiation with a frequency of 3.2 THz. In addition, all of the investigated plastics are mostly transparent for THz radiation, which makes imaging of these materials feasible. Based on these basic properties, it will be possible to image and identify these types of plastic.

The recent advent of quantum cascade lasers (QCLs) enables room-temperature mid-infrared spectrometer operation which is particularly favourable for industrial process monitoring and control, i.e. the detection of transient and stable molecular species. Conversely, fluorocarbon containing radio-frequency discharges are of special interest for plasma etching and deposition as well as for fundamental studies on gas phase and plasma surface reactions. The application of QCL absorption spectroscopy to such low pressure plasmas is typically hampered by non-linear effects connected with the pulsed mode of the lasers. Nevertheless, adequate calibration can eliminate such effects, especially in the case of complex spectra where single line parameters are not available. In order to facilitate measurements in fluorocarbon plasmas, studies on complex spectra of CF4 and C3F8 at 7.86 μm (1269 – 1275 cm-1) under low pressure conditions have been performed. The intra-pulse mode, i.e. pulses of up to 300 ns, was applied yielding highly resolved spectral scans of ∼ 1 cm-1 coverage. Effective absorption cross sections were determined and their temperature dependence was studied in the relevant range up to 400 K and found to be non-negligible.

We present a Green's function based treatment of the effects of electron-phonon coupling on transport through a molecular quantum dot in the quantum limit. Thereby we combine an incomplete variational Lang-Firsov approach with a perturbative calculation of the electron-phonon self energy in the framework of generalised Matsubara Green functions and a Landauer-type transport description. Calculating the ground-state energy, the dot single-particle spectral function and the linear conductance at finite carrier density, we study the low-temperature transport properties of the vibrating quantum dot sandwiched between metallic leads in the whole electron-phonon coupling strength regime. We discuss corrections to the concept of an anti-adiabatic dot polaron and show how a deformable quantum dot can act as a molecular switch.

A quantum kinetic approach is presented to investigate the energy relaxation of dense strongly coupled two-temperature plasmas. We derive a balance equation for the mean total energy of a plasma species including a quite general expression for the transfer rate. An approximation scheme is used leading to an expression of the transfer rates for systems with coupled modes relevant for the warm dense matter regime. The theory is then applied to dense beryllium plasmas under conditions such as realized in recent experiments. Special attention is paid to the influence of correlation and quantum effects on the relaxation process.

We discuss a numerical method to study electron transport in mesoscopic devices out of equilibrium. The method is based on the solution of operator equations of motion, using efficient Chebyshev time propagation techniques. Its peculiar feature is the propagation of operators backwards in time. In this way the resource consumption scales linearly with the number of states used to represent the system. This allows us to calculate the current for non-interacting electrons in large one-, two- and three-dimensional lead-device configurations with time-dependent voltages or potentials. We discuss the technical aspects of the method and present results for an electron pump device and a disordered system, where we find transient behaviour that exists for a very long time and may be accessible to experiments.

The properties of the ion feature of the Thomson scattering signal are investigated. Firstly, the description of the atomic form factor by hydrogen-like wave functions is reviewed and better screening charges are obtained. Then the ionic structure in systems with several ion species is calculated from the HNC integral equation.

The interaction of partially ionized plasmas with an electromagnetic field is investigated using quantum statistical methods. A general statistical expression for the current density of a plasma in an electromagnetic field is presented and considered in the high field regime. Expressions for the collisional absorption are derived and discussed. Further, partially ionized plasmas are considered. Plasma Bloch equations for the description of bound-free transitions are given and the absorption coefficient as well as rate coefficients for multiphoton ionization are derived and numerical results are presented.

Collisional absorption of dense fully ionized plasmas in strong high-frequency laser fields is investigated in the non-relativistic case. Quantum statistical methods are used as well as molecular dynamics simulations. In the quantum statistical expressions for the electrical current density and the electron-ion collision frequency–valid for arbitrary field strength–strong correlations are taken into account. In addition, molecular dynamic simulations were performed to calculate the heating of dense plasmas in laser fields. Comparisons with the analytic results for different plasma parameters are given. Isothermal plasmas as well as two-temperature plasmas are considered.

We investigate the equilibration of nonideal plasmas from initial states where each species has already established a Maxwellian distribution, but the species temperatures and the chemical composition are not in equilibrium. On the basis of quantum kinetic equations, we derive hydrodynamic balance equations for the species densities and temperatures. The coupled density-temperature relaxation is then given in terms of the energy transfer between the subsystems and the population kinetics. We use the Landau-Spitzer approach for the energy transfer rates and a system of rate equations to describe the nonequilibrium plasma composition. Nonideality corrections are included in the rate coefficients and as potential energy contributions in the temperature equations on the simplest level of a Debye shift.

Colossal magneto-resistance manganites are characterized by a complex interplay of charge, spin, orbital and lattice degrees of freedom. Formulating microscopic models for these compounds aims at meeting two conflicting objectives: sufficient simplification without excessive restrictions on the phase space. We give a detailed introduction to the electronic structure of manganites and derive a microscopic model for their low-energy physics. Focusing on short-range electron–lattice and spin–orbital correlations we supplement the modelling with numerical simulations.

The region surrounding the excitonic insulator phase is a three-component plasma composed of electrons, holes, and excitons. Due to the extended nature of the excitons, their presence influences the surrounding electrons and holes. We analyze this correlation. To this end, we calculate the density of bound electrons, the density of electrons in the correlated state, the momentum-resolved exciton density, and the momentum-resolved density of electron-hole pairs that are correlated but unbound. We find qualitative differences in the electron-hole correlations between the weak-coupling and the strong-coupling regime.

Abstract Based on the analysis of electron density Ne profiles (Grahamstown ionosonde), a case study of the height‐dependent ionospheric response to two 27‐day solar rotation periods in 2019 is performed. A well‐defined sinusoidal response is observed for the period from 27 April 2019 to 24 May 2019 and reproduced with a Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model simulation. The occurring differences between model and observations as well as the driving physical and chemical processes are discussed based on the height‐dependent variations of Ne and major species. Further simulations with an artificial noise free sinusoidal solar flux input show that the Ne delay is defined by contributions due to accumulation of O+ at the Ne peak (positive delay) and continuous loss of O2+ ${\mathrm{O}}_{2}^{+}$ in the lower ionosphere (negative delay). The neutral parts' 27‐day signatures show stronger phase shifts. The time‐dependent and height‐dependent impact of the processes responsible for the delayed ionospheric response can therefore be described by a joint analysis of the neutral and ionized parts. The return to the initial ionospheric state (and thus the loss of the accumulated O+) is driven by an increase of downward transport in the second half of the 27‐day solar rotation period. For this reason, the neutral vertical winds (upwards and downwards) and their different height‐dependent 27‐day signatures are discussed. Finally, the importance of a wavelength‐dependent analysis, statistical methods (superposed epoch analysis), and coupling with the middle atmosphere is discussed to outline steps for future analysis.

Abstract We formulate exact generalized nonequilibrium fluctuation relations for the quantum mechanical harmonic oscillator coupled to multiple harmonic baths. Each of the different baths is prepared in its own individual (in general nonthermal) state. Starting from the exact solution for the oscillator dynamics we study fluctuations of the oscillator position as well as of the energy current through the oscillator under general nonequilibrium conditions. In particular, we formulate a fluctuation–dissipation relation for the oscillator position autocorrelation function that generalizes the standard result for the case of a single bath at thermal equilibrium. Moreover, we show that the generating function for the position operator fulfils a generalized Gallavotti–Cohen-like relation. For the energy transfer through the oscillator, we determine the average energy current together with the current fluctuations. Finally, we discuss the generalization of the cumulant generating function for the energy transfer to nonthermal bath preparations.

AbstractGas puff modulation experiments are performed at ASDEX Upgrade in L-mode plasmas. We model the discharge with the ASTRA transport code in order to determine transport coefficients outside of a normalized radius of ρ pol = 0.95. The experimental data is consistent with a range of particle diffusivities and pinch velocities of the order of D = (0.20 ± 0.13) m2 s−1 and v = (−1 ± 2) m s−1, respectively. The electron temperature response caused by the gas modulation permits to estimate also that heat diffusivity χ e increases almost linearly when collisionality rises due to fuelling. The fuelling particle flux is amplified by recycling, overcompensating losses.

Synopsis The cryogenic storage ring (CSR) for positive and negative atomic, molecular and cluster ions is starting operation at the Max Planck Institute for Nuclear Physics in Heidelberg.

Synopsis A network of ion sources is being developed on the 300-kV acceleration platform of the cryogenic storage ring (CSR) at the Max-Planck-Institut für Kernphysik. It consists of several types of sources like a metal ion sputtering source (MISS), a Penning source, a laser vaporization (LVAP) source, and an electrospray ionization (ESI) source to produce a large variety of ions which can be studied for photon and electron interaction in a ro-vibrationally cold environment. Furthermore a storage device such as a radiofrequency quadrupole (RFQ) is foreseen for internal state cooling and accumulation of rarely produced species.

Detecting changes in plasmas is compulsory for control and the detection of novelties. Moreover, automated novelty detection allows one to investigate large data sets to substantially enhance the efficiency of data mining approaches. To this end we introduce permutation entropy (PE) for the detection of changes in plasmas. PE is an information-theoretic complexity measure based in fluctuation analysis that quantifies the degree of randomness (resp. disorder, unpredictability) of the ordering of time series data. This method is computationally fast and robust against noise, which allows the evaluation of large data sets in an automated procedure. PE is applied on electron cyclotron emission and soft x-ray measurements in different Wendelstein 7-X low-iota configuration plasmas. A spontaneous transition to high core-electron temperature (Te) was detected, as well as a localized low-coherent intermittent oscillation which ceased when Te increased in the transition. The results are validated with spectrogram analysis and provide evidence that a complexity measure such as PE is a method to support in-situ monitoring of plasma parameters and for novelty detection in plasma data. Moreover, the acceleration in processing time offers implementations of plasma-state-detection that provides results fast enough to induce control actions even during the experiment.

Abstract Nanoscale multilayer thin films of W and PC (Polycarbonate) show, due to the great difference of the components’ characteristics, fascinating properties for a variety of possible applications and provide an interesting research field, but are hard to fabricate with low layer thicknesses. Because of the great acoustic mismatch between the two materials, such nanoscale structures are promising candidates for new phononic materials, where phonon propagation is strongly reduced. In this article we show for the first time that W/PC-multilayers can indeed be grown with high quality by pulsed laser deposition. We analyzed the polymer properties depending on the laser fluence used for deposition, which enabled us to find best experimental conditions for the fabrication of high-acoustic-mismatch W/PC multilayers. The multilayers were analyzed by fs pump-probe spectroscopy showing that phonon dynamics on the ps time-scale can strongly be tailored by structural design. While already periodic multilayers exhibit strong phonon localization, especially aperiodic structures present outstandingly low phonon propagation properties making such 1D-layered W/PC nano-structures interesting for new phononic applications.

Abstract Experimental studies on dusty plasmas containing systems of (super-)paramagnetic dust particles are presented. In our experiments, external (homogeneous as well as inhomogeneous) magnetic fields in the mT range are applied to study the effect on single particles or few-particle systems that are trapped inside the sheath region. The behavior of the paramagnetic dust particles is considerably different than that of dielectric plastic particles, which are widely used in dusty plasmas. It is revealed that especially non-magnetic contributions play an important role in the interaction between superparamagnetic particles.

Abstract The spectral properties of three-dimensional dust clusters confined in gaseous discharges are investigated using both a fluid mode description and the normal mode analysis (NMA). The modes are analysed for crystalline clusters as well as for laser-heated fluid-like clusters. It is shown that even for clusters with low particle numbers and under presence of damping fluid modes can be identified. Laser-heating leads to the excitation of several, mainly transverse, modes. The mode frequencies are found to be nearly independent of the coupling parameter and support the predictions of the underlying theory. The NMA and the fluid mode spectra demonstrate that the wakefield attraction is present for the experimentally observed Yukawa balls at low pressure. Both methods complement each other, since NMA is more suitable for crystalline clusters, whereas the fluid modes allow to explore even fluid-like dust clouds.

Molecular surface gradients can constitute electric field landscapes and serve to control local cell adhesion and migration. Cellular responses to electric field landscapes may allow the discovery of routes to improve osseointegration of implants. Flat molecule aggregate landscapes of amine- or carboxyl-teminated dendrimers, amine-containing protein and polyelectrolytes were prepared on glass to provide lateral electric field gradients through their differing zeta potentials compared to the glass substrate. The local as well as the mesoscopic morphological responses of adhered osteoblasts (MG-63) with respect to the stripes were studied by means of Scanning Ion Conductance Microscopy (SICM) and Fluorescence Microscopy, in situ. A distinct spindle shape oriented parallel to the surface pattern as well as a preferential adhesion of the cells on the glass site have been observed at a stripe and spacing width of 20 μm. Excessive ruffling is observed at the spindle poles, where the cells extend. To explain this effect of material preference and electro-deformation, we put forward a retraction mechanism, a localized form of double-sided cathodic taxis.

As a new field of oxidative stress-based therapy, cold physical plasma is a promising tool for several biomedical applications due to its potential to create a broad diversity of reactive oxygen and nitrogen species (RONS). Although proposed, the impact of plasma-derived RONS on the cell membrane lipids and properties is not fully understood. For this purpose, the changes in the lipid bilayer functionality under oxidative stress generated by an argon plasma jet (kINPen) were investigated by electrochemical techniques. In addition, liquid chromatography-tandem mass spectrometry was employed to analyze the plasma-induced modifications on the model lipids. Various asymmetric bilayers mimicking the structure and properties of the erythrocyte cell membrane were transferred onto a gold electrode surface by Langmuir-Blodgett/Langmuir-Schaefer deposition techniques. A strong impact of cholesterol on membrane permeabilization by plasma-derived species was revealed. Moreover, the maintenance of the barrier properties is influenced by the chemical composition of the head group. Mainly the head group size and its hydrogen bonding capacities are relevant, and phosphatidylcholines are significantly more susceptible than phosphatidylserines and other lipid classes, underlining the high relevance of this lipid class in membrane dynamics and cell physiology.

Abstract The surface charge distribution deposited by the effluent of a dielectric barrier discharge driven atmospheric pressure plasma jet on a dielectric surface has been studied. For the first time, the deposition of charge was observed phase resolved. It takes place in either one or two events in each half cycle of the driving voltage. The charge transfer could also be detected in the electrode current of the jet. The periodic change of surface charge polarity has been found to correspond well with the appearance of ionized channels left behind by guided streamers (bullets) that have been identified in similar experimental situations. The distribution of negative surface charge turned out to be significantly broader than for positive charge. With increasing distance of the jet nozzle from the target surface, the charge transfer decreases until finally the effluent loses contact and the charge transfer stops.

Formation of singly and doubly charged Arq+ and Tiq+ (q = 1,2) and of molecular Ar 2 +, ArTi+, and Ti 2 + ions in a direct current magnetron sputtering discharge with a Ti cathode and argon as working gas was investigated with the help of energy-resolved mass spectrometry. Measured ion energy distributions consist of low-energy and high-energy components resembling different formation processes. Intensities of Ar 2 + and ArTi+ dimer ions strongly increase with increasing gas pressure. Addition of oxygen gas leads to the formation of positively charged O+, O2 +, and TiO+ and of negatively charged O− and O2 - ions.

AbstractWe propose a new scattering mechanism of Rydberg excitons, i.e., those with high principal quantum numbers, namely scattering by coupled LO phonon-plasmon modes, which becomes possible due to small differences in energies of the states due to different quantum defects. Already in very low-density electron–hole plasmas these provide a substantial contribution to the excitonic linewidth. This effect should allow determining plasma densities by a simple line shape analysis. Whenever one expects that low-density electron–hole plasma is present the plasmon induced broadening is of high significance and must be taken into account in the interpretation.

AbstractPulsed streamer discharges submerged in water have demonstrated potential in a number of applications. Especially the generation of discharges by short high-voltage pulses in the nanosecond range has been found to offer advantages with respect to efficacies and efficiencies. The exploited plasma chemistry generally relies on the initial production of short-lived species, e.g. hydroxyl radicals. Since the diagnostic of these transient species is not readily possible, a quantification of hydrogen peroxide provides an adequate assessment of underlying reactions. These conceivably depend on the characteristics of the high-voltage pulses, such as pulse duration, pulse amplitude, as well as pulse steepness.A novel electrochemical flow-injection system was used to relate these parameters to hydrogen peroxide concentrations. Accordingly, the accumulated hydrogen peroxide production for streamer discharges ignited in deionized water was investigated for pulse durations of 100 ns and 300 ns, pulse amplitudes between 54 kV and 64 kV, and pulse rise times from 16 ns to 31 ns. An independent control of the individual pulse parameters was enabled by providing the high-voltage pulses with a Blumlein line. Applied voltage, discharge current, optical light emission and time-integrated images were recorded for each individual discharge to determine dissipated energy, inception statistic, discharge expansion and the lifetime of a discharge.Pulse steepness did not affect the hydrogen peroxide production rate, but an increase in amplitude of 10 kV for 100 ns pulses nearly doubled the rate to (0.19 ± 0.01) mol l−1 s−1, which was overall the highest determined rate. The energy efficiency did not change with pulse amplitude, but was sensitive to pulse duration. Notably, production rate and efficiency doubled when the pulse duration decreased from 300 ns to 100 ns, resulting in the best peroxide production efficiency of (9.2 ± 0.9) g kWh−1. The detailed analysis revealed that the hydrogen peroxide production rate could be described by the energy dissipation in a representative single streamer. The production efficiency was affected by the corresponding discharge volume, which was comprised by the collective volume of all filaments. Hence, dissipating more energy in a filament resulted in an increased production rate, while increasing the relative volume of the discharge compared to its propagation time increased the energy efficiency.

The behavior of a single porous particle with a diameter of 250 μm levitating in a radiofrequency (RF) plasma under pulsed argon ion beam bombardment was investigated. The motion of the particle under the action of the ion beam was observed to be an oscillatory motion. The Fourier-analyzed motion is dominated by the excitation frequency of the pulsed ion beam and odd higher harmonics, which peak near the resonance frequency. The appearance of even harmonics is explained by a variation of the particles's charge depending on its position in the plasma sheath. The Fourier analysis also allows a discussion of neutral and ion forces. The particle's charge was derived and compared with theoretical estimates based on the orbital motion-limited (OML) model using also a numerical simulation of the RF discharge. The derived particle's charge is about 7–15 times larger than predicted by the theoretical models. This difference is attributed to the porous structure of the particle.

An interesting aspect in the research of complex (dusty) plasmas is the experimental study of the interaction of micro-particles with the surrounding plasma for diagnostic purposes. Local electric fields can be determined from the behaviour of particles in the plasma, e.g. particles may serve as electrostatic probes. Since in many cases of applications in plasma technology it is of great interest to describe the electric field conditions in front of floating or biased surfaces, the confinement and behaviour of test particles is studied in front of floating walls inserted into a plasma as well as in front of additionally biased surfaces. For the latter case, the behaviour of particles in front of an adaptive electrode, which allows for an efficient confinement and manipulation of the grains, has been experimentally studied in terms of the dependence on the discharge parameters and on different bias conditions of the electrode. The effect of the partially biased surface (dc and rf) on the charged micro-particles has been investigated by particle falling experiments. In addition to the experiments, we also investigate the particle behaviour numerically by molecular dynamics, in combination with a fluid and particle-in-cell description of the plasma.

AbstractThe performance of a positively biased external ring anode in combination with a hollow cathode (HC) discharge or a magnetron sputtering (MS) discharge, both with a Ti cathode and with Ar as working gas, is investigated. Plasma and floating potential increase as function of anode voltage. Energy-resolved mass spectrometry reveals that the kinetic energy of argon and titanium ions is enhanced by a positive anode voltage allowing for an effective energy control of plasma ions.

Abstract We propose a setup enabling electron energy loss spectroscopy to determine the density of the electrons accumulated by an electropositive dielectric in contact with a plasma. It is based on a two-layer structure inserted into a recess of the wall. Consisting of a plasma-facing film made out of the dielectric of interest and a substrate layer, the structure is designed to confine the plasma-induced surplus electrons to the region of the film. The charge fluctuations they give rise to can then be read out from the backside of the substrate by near specular electron reflection. To obtain in this scattering geometry a strong charge-sensitive reflection maximum due to the surplus electrons, the film has to be most probably pre-n-doped and sufficiently thin with the mechanical stability maintained by the substrate. Taking electronegative CaO as a substrate layer we demonstrate the feasibility of the proposal by calculating the loss spectra for Al2O3, SiO2, and ZnO films. In all three cases we find a reflection maximum strongly shifting with the density of the surplus electrons and suggest to use it for charge diagnostics.

Abstract The presented work highlights the role of residual weakly-bound surface electrons acting as an effective seed electron reservoir that favors the pre-ionization of diffuse barrier discharges (BDs). A glow-like BD was operated in helium at a pressure of 500 mbar in between two plane electrodes each covered with float glass at a distance of 3 mm.The change in discharge development due to laser photodesorption of surface electrons was studied by electrical measurements and optical emission spectroscopy. Moreover, a 1D numerical fluid model of the diffuse discharge allowed the simulation of the laser photodesorption experiment, the estimation of the released surface electrons, and the understanding of their impact on the reaction kinetics in the volume. The breakdown voltage is clearly reduced when the laser beam at photon energy of 2.33 eV hits the cathodic dielectric that is charged with residual electrons during the discharge pre-phase. According to the adapted simulation, the laser releases only a small amount of surface electrons in the order of 10 pC. Nevertheless, this significantly supports the pre-ionization. Using a lower photon energy of 1.17 eV, the transition from the glow mode to the Townsend mode is induced due to a much higher electron yield up to 1 nC. In this case, both experiment and simulation indicate a retarded stepwise release of surface electrons initiated by the low laser photon energy.

Abstract In this series of two papers, the E-H transition in a planar inductively coupled radio frequency discharge (13.56 MHz) in pure oxygen is studied using comprehensive plasma diagnostic methods. The electron density serves as the main plasma parameter to distinguish between the operation modes. The (effective) electron temperature, which is calculated from the electron energy distribution function and the difference between the floating and plasma potential, halves during the E-H transition. Furthermore, the pressure dependency of the RF sheath extension in the E-mode implies a collisional RF sheath for the considered total gas pressures. The gas temperature increases with the electron density during the E-H transition and doubles in the H-mode compared to the E-mode, whereas the molecular ground state density halves at the given total gas pressure. Moreover, the singlet molecular metastable density reaches 2% in the E-mode and 4% in the H-mode of the molecular ground state density. These measured plasma parameters can be used as input parameters for global rate equation calculations to analyze several elementary processes. Here, the ionization rate for the molecular oxygen ions is exemplarily determined and reveals, together with the optical excitation rate patterns, a change in electronegativity during the mode transition.

AbstractFluctuations of electron cyclotron emission (ECE) signals are analyzed for differently heated Wendelstein 7-X plasmas. The fluctuations appear to travel predominantly on flux surfaces and are used as ‘tracers’ in multivariate time series. Different statistical techniques are assessed to reveal the coupling and information entropy-based coupling analysis are conducted. All these techniques provide evidence that the fluctuation analysis allows one to check the consistency of magneto-hydrodynamic (MHD) equilibrium calculations. Expanding the suite of techniques applied in fusion data analysis, partial mutual information (PMI) analysis is introduced. PMI generalizes traditional partial correlation (Frenzel and Pompe Phys. Rev. Lett. 99 204101) and also Schreiber’s transfer entropy (Schreiber 2000 Phys. Rev. Lett. 85 461). The main additional capability of PMI is to allow one to discount for specific spurious data. Since PMI analysis allows one to study the effect of common drivers, the influence of the electron cyclotron resonance heating on the mutual dependencies of simultaneous ECE measurements was assessed. Additionally, MHD mode activity was found to be coupled in a limited volume in the plasma core for different plasmas. The study reveals an experimental test for equilibrium calculations and ECE radiation transport.

AbstractWe present an algorithm to reconstruct the three-dimensional positions of particles in a dense cloud of particles in a dusty plasma using a convolutional neural network. The approach is found to be very fast and yields a relatively high accuracy. In this paper, we describe and examine the approach regarding the particle number and the reconstruction accuracy using synthetic data and experimental data. To show the applicability of the approach the 3D positions of particles in a dense dust cloud in a dusty plasma under weightlessness are reconstructed from stereoscopic camera images using the prescribed neural network.

Abstract Single self-stabilized discharge filaments were investigated in the plane-parallel electrode configuration. The barrier discharge was operated inside a gap of 3 mm shielded by glass plates to both electrodes, using helium-nitrogen mixtures and a square-wave feeding voltage at a frequency of 2 kHz. The combined application of electrical measurements, ICCD camera imaging, optical emission spectroscopy and surface charge diagnostics via the electro-optic Pockels effect allowed the correlation of the discharge development in the volume and on the dielectric surfaces. The formation criteria and existence regimes were found by systematic variation of the nitrogen admixture to helium, the total pressure and the feeding voltage amplitude. Single self-stabilized discharge filaments can be operated over a wide parameter range, foremost, by significant reduction of the voltage amplitude after the operation in the microdischarge regime. Here, the outstanding importance of the surface charge memory effect on the long-term stability was pointed out by the recalculated spatio-temporally resolved gap voltage. The optical emission revealed discharge characteristics that are partially reminiscent of both the glow-like barrier discharge and the microdischarge regime, such as a Townsend pre-phase, a fast cathode-directed ionization front during the breakdown and radially propagating surface discharges during the afterglow.

In this work, spatial distributions for reactive stable and transient species that are involved in the reaction cycle of H2O2, a key species for biomedical applications, were determined directly in the effluent of a kINPen-sci plasma jet. The small diameter of cold atmospheric pressure plasma jets and their operation at atmospheric pressure that causes strong quenching reactions make diagnostics challenging. Here, various diagnostic techniques have been employed and adapted for the use in the effluent of a cold atmospheric pressure plasma jet, which were laser atomic absorption spectroscopy (LAAS) at 811.5 nm for the detection of Ar(3P2), picosecond two-photon absorption laser-induced fluorescence spectroscopy (ps-TALIF) at 225 nm and 205 nm for the detection of O and H atoms, respectively, and continuous wave cavity ring-down spectroscopy (cw-CRDS) at 1.506 µm for the detection of HO2, and cw-CRDS at 8000 µm for the detection of H2O2. All these methods provide absolute number densities. In this work, spatial distributions within the small diameter of the effluent of a CAPJ were obtained, which have not been reported so far literature. In order to overcome the line-of-sight limitations of CRDS, radial scans were performed and transformed into a spatial distribution by using Abel inversion. Based on the determined spatial density distributions for H atoms, O atoms, HO2 radicals, and H2O2 molecules, together with the investigated impact of humidity in the feed gas on the excitation dynamics and the production of Ar(3P2), and finally on a comparison of the experimental results to a plasma chemical and reacting flow model, three different zones with varying reaction kinetics were identified. The densities close to the nozzle of the kINPen-sci plasma jet were dominated by reactions within the plasma zone including the dissociation of H2O added to the Ar feed gas and O2 that was presumably transferred into the plasma zone by counter-propagating ionisation waves. Notably, also the larger molecules, such as HO2 and H2O2 were mainly formed within the plasma zone of the plasma jet. Between 1.5 mm and 5 mm below the nozzle, the atomic species and molecular radicals generated in the plasma zone were consumed by chemical reactions with the surrounding gas, whose composition was controlled by applying a gas curtain. At further distances from the nozzle, where typically biological samples are positioned, only H2O2 and HO2 were observed. With this work, it is successfully demonstrated that even for the small diameters of cold atmospheric pressure plasma jets the determination of spatial profiles for reactive transient and stable species is possible within the effluent. By combining the experimental results, important insights into the formation and consumption of H2O2 and its precursors were gained, which are essential for the understanding of use of plasmas in biomedical applications.

In this thesis, charge transport at the plasma-wall interface is investigated theoretically, on a semiclassical, microscopic level. Based on the Boltzmann and Poisson equations a set of equations is derived and numerically solved to model charge carriers both within a semiconducting wall and a gaseous plasma in front of it. While the plasma is considered collision-free, within the solid, phonon collisions, as well as recombination processes between conduction band electrons and valence band holes are considered. This results, for the first time, in a self-consistent modeling of both the gaseous electron-ion plasma and the electron-hole plasma in the solid on the same footing. Utilizing specific approximations for different physical scenarios, numerical solutions are presented both for the floating and the electronically contacted (biased) interface. In the latter case, the current voltage characteristic is calculated and shown to heavily depend on the charge kinetics within the wall. Furthermore, we present optical methods to measure the wall charge noninvasively. These utilize the influence of the deposited surplus charges on the optical reflection coefficient of the surface. By calculating the optical response of these charges, we show that the magnitude of the surface charge can be inferred from the change in the reflectivity of the surface caused by the presence of the plasma. While nonlocal effects are considered, it is shown analytically and numerically that these can be neglected at the scales of the considered physical systems.

Indium-cluster anions In−nare probed for delayed dissociation by photoexcitation in a multi-reflection time-of-flight device. In addition to prompt dissociation with below-microsecond decay constants, we observe reactionson timescales of several tens to hundreds of microseconds. These time-resolved decay-rate measurements reveala power-law behavior in time which can be traced back to the clusters’ energy distribution due to their productionby laser ablation in high vacuum. Modeling energy distributions from such a production allows us to connect thecluster-specific dissociation energy with the ensemble temperature through experimentally determined power-law exponents.

This work investigates turbulence in the core plasma of the optimised stellarator Wendelstein 7-X. It focuses on experimental characterisation and evaluation of the electrostatic micro-instabilities, which drive turbulent fluctuations, and the saturation of turbulence by zonal flows. Expectations for Wendelstein 7-X are formulated by reviewing theoretical work and with the help of gyrokinetic simulations. The experimental analysis centres on line-integrated density fluctuation measurements with the phase contrast imagining diagnostic in electron cyclotron heated hydrogen discharges. An absolute amplitude calibration was implemented, and a method for reliable determination of dominant phase velocities in wavenumber-frequency spectra of density fluctuations has been developed. Line-averaged density fluctuation levels are observed to vary between magnetic configurations. The wavenumber spectra exhibit a dual cascade structure, indicating fully developed turbulence. The dominant instability driving turbulent density fluctuations on transport relevant scales is identified as ion-temperaturegradient- driven modes, which are mainly localised in the edge region of the confined plasma. Despite the line-integrated nature of the measurement, the localisation of density fluctuations is shown by comparing their dominant phase velocity with the radial profile of the E × B rotation velocity due to the ambipolar neoclassical electric field. Nonlinear gyrokinetic simulations and a simplified plasma rotation model within a synthetic diagnostic confirm the localisation. Oscillations of the dominant phase velocity indicate the existence of zonal flows as a saturation mechanism of ion-temperaturegradient- driven turbulence. A direct effect on turbulent density fluctuation amplitudes and radial transport is observed.

Synopsis Polyanionic metal clusters are produced by electron attachment in both Paul and Penning traps. After size and charge-state selection, the cluster properties are further investigated by various methods including photo-dissociation. Depending on the particular cluster species various decay modes are observed.

Cell mechanical properties reveal substantial information on cell state and function. Utilizing mechanics as a label-free biomarker allows for investigation of fundamental cellular processes as well as biomedical applications, e.g., disease diagnosis. High-throughput methods for accessing the elastic properties of cells in suspension from hydrodynamic deformation in a microfluidic constriction are available with real-time analysis rates of up to 1000 cells per second. However, accessing elastic as well as viscous properties of cells and multicellular systems in suspension as well as adhered to surfaces at high throughput has not been possible so far. In this thesis, I approached this question and developed as well as applied microfluidic and holographic technologies to analyze the viscoelastic properties of single cells and multicellular aggregates, respectively. First, I demonstrated that real-time deformability cytometry (RT-DC) can be applied in transfusion medicine, where the highest quality standards have to be maintained while blood product release is time-critical. We showed for platelet and red blood cell concentrates as well as for hematopoietic stem cells that their mechanical properties can be used for label-free quality assessment. The results have been published in Lab on a Chip (Aurich et al. 2020). For RT-DC and many other methods based on hydrodynamic deformation, the constriction size has to be adapted to the objects of interest to allow for a shear-induced deformation. We introduced virtual fluidic channels, which are established by two co-flowing aqueous polymer solutions. Virtual fluidic channels can be precisely adjusted in their cross section, allowing for mechanical phenotyping of single cells as well as cell clusters or tissue spheroids in one microfluidic system. Importantly, measurements can also be performed in standard microfluidic geometries beyond soft lithography, e.g., in the cuvette of a flow cytometer. For cell spheroids as a model system for multicellular aggregates, we show a 10-fold lower Young's modulus of the tissue compared to single-cell mechanics, suggesting cell-cell and cell-matrix interactions being potential contributors to the mechanics of multicellular aggregates. Our work on virtual fluidic channels has been published in Nature Communications (Panhwar et al. 2020). Within this thesis, I expanded the high-throughput elastic phenotyping performed by RT-DC towards viscoelastic cell properties by developing dynamic real-time deformability cytometry (dRT-DC). Dynamic tracking of cells while passing the microfluidic constriction allows to access steady-state (elasticity) and time-dependent (viscosity) material properties for a complete viscoelastic characterization of cells in suspension at high throughput. I introduced a shape mode decomposition based on a Fourier transformation, which allows to disentangle the superimposed stress responses to an extensional stress at the channel inlet and a constant shear stress in the channel. These hydrodynamic stress distributions are present in almost every microfluidic channel geometry. From the separated stress responses, viscoelastic material properties can be determined independent of cell shape. We demonstrated experimentally the sensitivity of dRT-DC to cytoskeletal alterations and confirmed the validity of the method by reference measurements on calibrated hydrogel beads. In our work, we also presented a viscoelastic fingerprint of the major subpopulations of peripheral blood: erythrocytes, granulocytes, and peripheral blood mononuclear cells (PBMCs) (e.g., lymphocytes and monocytes), all characterized by the same method. The technique and the results have been published in Nature Communications (Fregin et al. 2019). In cell mechanical methods based on hydrodynamic deformation, cell shape is usually monitored while a stress is applied. For extraction of material properties as well as for studying shape dynamics, it is essential to describe cell shape yielding highest strain differences for a given microfluidic system and experimental setting. Using dRT-DC, I compared nine different shape descriptors to analyze cell deformation in an extensional as well as shear flow. A relaxation time analysis was performed on different levels of data aggregation from single cells to an ensemble scale. I demonstrated that the steady-state deformation can be predicted from stress response curves without them reaching the steady-state. This is important for cell mechanical measurements in microfluidic systems as the characteristic times are unknown in general and as the channel length is fixed. In addition, by introducing a cut-off criterion for how much of the response trace needs to be captured within the channel, the analysis time per cell can be reduced while material properties can still be extracted. Performing simulations, I compared the accuracy of relaxation times extracted from ensemble and single-cell studies under experimental conditions. Introducing a scoring system to evaluate which combinations of shape descriptors and analysis strategies provide biggest effect size, we concluded that single-cell analyses in an extensional flow are most sensitive to cytoskeletal modifications independent of shape parametrization. The manuscript was submitted to the Biophysical Journal. Finally, I translated the fast non-contact cell mechanical probing from suspension to adherent cells. No such technology has been available and with the majority of cells being adherent, a robust label-free method for mechanophenotyping at high-throughput is required. Within this thesis, I have introduced and realized a new concept: holographic vibration spectroscopy (HVS), where adherent cells are mechanically excited on a vibrating surface while their height oscillations are measured optically. Analysis is done in an interferometric heterodyne setup by using frequency multiplexing and time-averaged holography in off-axis configuration. Based on interference images captured by a high-speed complementary metal-oxide-semiconductor (CMOS) camera, I established a mathematical model to reconstruct the vibration amplitude of adherent cells as well as their retardation phase compared to the exciting vibration. From the amplitude and phase response, viscoelastic parameters can be derived, which have to be investigated in subsequent studies. In summary, I introduced in my work two high-throughput methods for the viscoelastic characterization of suspended as well as adherent cells while highlighting applications in tissue mechanics and transfusion medicine that are relevant not only in basic but also in translational research.

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.

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.

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.

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.