Polarisationsspektroskopie für die Untersuchung von Plasmaprozessen

Die vorliegende Dissertation beschäftigt sich mit der laserdiagnostischen Messmethode der Polarisationsspektroskopie mit dem Ziel, ihr Potential für Forschungs- und Entwicklungsanwendungen in der Plasmatechnologie zu demonstrieren. Hierfür wird ein Messaufbau für die Polarisationsspektroskopie entwickelt. Er erlaubt spektral hochauflösende Messungen im Wellenlängenbereich um 226 nm. In diesem Spektralbereich kann die Absorption von O, O2 und NO untersucht werden. Diese drei Spezies sind für verschiedene Plasmaprozesse wie die Simulation von atmosphärischen Eintrittsbedingungen in Plasmawindkanälen sowie der Erzeugung von Plasma bei atmosphärischem Druck für NOx-Syntheseprozesse oder den gezielten Abbau von klimaschädlichen Abgasen wie CO2 von Bedeutung. Der Versuchsaufbau wird anhand von Messungen des Xenon 7p[1/2]0 Zwei-Photonen Übergangs kalibriert. Mit einer speziell für die Polarisationsspektroskopie entwickelten Kaltgaszelle können systematische Untersuchungen an Xenon bei präzise kontrollierbaren Drücken vorgenommen werden. Für den Messaufbau wird eine instrumentelle Linienverbreiterung von 0,264 pm festgestellt. Erstmalig wird die druckabhängige Verbreiterung und die druckabhängige Rotverschiebung von Xenon 7p[1/2]0 gemessen. Die Druckverbreiterung beträgt 1,475 pm/bar. Die Rotverschiebung ist 1,685 pm/bar. Das linear vom Druck abhängige Verhalten dieser Eigenschaften des Xenonübergangs wird verwendet um die Modellierung der Polarisationslinienform zu verifizieren. Auf Basis der Untersuchungen an Xenon kann ein unteres Detektionslimit für die messbare Teilchendichte atomaren Sauerstoffs für den Messaufbau zu nO ≥3, 29⋅1023 m−3 bestimmt werden. Möglichkeiten die Empfindlichkeit signifikant zu erhöhen, sind die Verwendung von Polarisatoren mit einem besseren Auslöschungsvermögen sowie Laserpulsen höherer Energie. Für die Untersuchung der molekularen Spezies O2 und NO wird ein Line-by-Line Code für die Simulation von Polarisationsspektren von O2 Schumann-Runge B 3Σu− ← X 3Σg− und vier NO-Absorptionsübergängen (γ, β, δ, ϵ) entwickelt. Die Berücksichtigung der Prädissoziation und der damit verbundenen Verbreiterung der Rotationslinien ist von entscheidender Bedeutung für die korrekte Simulation der O2-Spektren. In der vorliegenden Dissertation wird O2 zum ersten mal mit der Polarisationsspektroskopie detektiert. Als Nachweis werden Messungen in reinem O2-Plasma durchgeführt. Dieses wird mit einer mikrowellengetriebenen Plasmaquelle bei Atmosphärendruck erzeugt. Eine Referenzbedingung zur Validierung des Simulationsprogramms unter der Annahme von Ttrans = Trot und Tvib = Tel wird definiert. Hierfür werden Messdaten aus der Entwicklungsphase der Plasmaquelle verwendet und der Plasmazustand wird emissionsspektroskopisch untersucht. Die simulierten Polarisationsspektren der Referenzbedingung stimmen sehr gut mit den gemessenen Spektren überein. Das Potential des Messverfahrens für die Untersuchung von Plasmaprozessen wird anhand von zwei Anwendungsfällen demonstriert. Hierfür werden Messungen im Resonator der Mikrowellenplasmaquelle bei Atmosphärendruck durchgeführt. In Luftplasma wird eine relative Teilchendichte nO2/nNO = 1500 detektiert. Der niedrige NO-Gehalt deutet darauf hin, dass die Bildung von NO vornehmlich in den Bereichen kälterer Strömung stattfindet. Messungen von O2 in CO2-Plasma zeigen, dass die Plasmabedingungen mit Trot = 2660 K und Tvib = 6115 K im thermischen Nichtgleichgewicht sind. Plasmabedingungen dieser Art begünstigen den effizienten Abbau von CO2, da Rückreaktionen nach der Dissoziation von CO2 unterbunden werden. Dies resultiert in einem erhöhten O2-Gehalt des CO2-Plasmas. Vergleichsmessungen in O2-Plasma bestätigen dies. Es wird festgestellt, dass das CO2-Plasma 2,4-mal mehr O2 enthält als in einem thermischen CO2-Plasma zu erwarten wäre. Die beiden Anwendungsfälle demonstrieren das Potential der Polarisationsspektroskopie als Instrument für die Erforschung und Entwicklung von Plasmaprozessen

CO2 dissociation using a lab-scale microwave plasma torch: an experimental study in view of industrial application

Under laboratory conditions, microwave plasma torches are known to be an energetically very efficient CO2 conversion technology, for pressures ranging from 100 mbar up to atmospheric pressure. However, issues relevant for industrial application such as the total energy efficiency, including the power consumption of peripheral equipment, the performance for impure CO2 streams (such as directly from carbon capture facilities) and the stability at long-term operation are usually not addressed. To fill that gap, a lab-scale plasma torch and the corresponding vacuum pump are connected to an energy meter system. Measured wall-plug energy efficiencies yielded values up to 17.9%, corresponding to an electrical power consumption of 19.6 kWh per produced Nm3 of carbon monoxide. Experiments with controlled amounts of impurities (Ar, N2, O2, real air and synthetic air) in the feed gas stream are performed. It is shown that small amounts of nitrogen can even increase energy efficiency whereas humidity in the CO2 stream might have an extremely detrimental effect on CO2 decomposition. Finally, a durability test over 29 h was performed, demonstrating that microwave plasma torch operation is very reproducible and stable in all figures of merit with short ramp-up times, making it a promising technology for intermittent operation on industrial scale

Extension of the plasma radiation database PARADE for the analysis of meteor spectra

The advancement in the acquisition of spectral data from meteors, as well as the capability to analyze meteoritic entries in ground testing facilities, requires the assessment of the performance of software tools for the simulation of spectra for different species. The Plasma Radiation Database, PARADE, is a line‐by‐line emission calculation tool. This article presents the extensions implemented for the simulation of meteor entries with the additional atomic species Na, K, Ti, V, Cr, Mn, Fe, Ca, Ni, Co, Mg, Si, and Li. These atoms are simulated and compared to ground testing spectra and to observed spectra from the CILBO observatory. The diatomic molecules AlO and TiO have now been added to the PARADE database. The molecule implementations have been compared to the results of a simple analytical program designed to approximate the vibrational band emission of diatomic molecules. AlO and TiO have been identified during the airborne observation campaigns of re‐entering man‐made objects WT1190F and CYGNUS OA6. Comparisons are provided showing reasonable agreement between observation and simulation.European Space AgencyHEFDiGProjekt DEA

Assessment of high enthalpy flow conditions for re-entry aerothermodynamics in the plasma wind tunnel facilities at IRS

This article presents the full operational experimental capabilities of the plasma wind tunnel facilities at the Institute of Space Systems at the University of Stuttgart. The simulation of the aerothermodynamic environment experienced by vehicles entering the atmosphere of Earth is attempted using three different facilities. Utilizing the three different facilities, the recent improvements enable a unique range of flow conditions in relation to other known facilities. Recent performance optimisations are highlighted in this article. Based on the experimental conditions demonstrated a corresponding flight scenario is derived using a ground-to-flight extrapolation approach based on local mass-specific enthalpy, total pressure and boundary layer edge velocity gradient. This shows that the three facilities cover the challenging parts of the aerothermodynamics along the entry trajectory from Low Earth Orbit. Furthermore, the more challenging conditions arising during interplanetary return at altitudes above 70 km are as well covered.Projekt DEA

Charge Pair Interactions in Transmembrane Helices and Turn Propensity of the Connecting Sequence Promote Helical Hairpin Insertion

α-Helical hairpins, consisting of a pair of closely spaced transmembrane (TM) helices that are connected by a short interfacial turn, are the simplest structural motifs found in multi-spanning membrane proteins. In naturally occurring hairpins, the presence of polar residues is common and predicted to complicate membrane insertion. We postulate that the pre-packing process offsets any energetic cost of allocating polar and charged residues within the hydrophobic environment of biological membranes. Consistent with this idea, we provide here experimental evidence demonstrating that helical hairpin insertion into biological membranes can be driven by electrostatic interactions between closely separated, poorly hydrophobic sequences. Additionally, we observe that the integral hairpin can be stabilized by a short loop heavily populated by turn-promoting residues. We conclude that the combined effect of TM¿TM electrostatic interactions and tight turns plays an important role in generating the functional architecture of membrane proteins and propose that helical hairpin motifs can be acquired within the context of the Sec61 translocon at the early stages of membrane protein biosynthesis. Taken together, these data further underline the potential complexities involved in accurately predicting TM domains from primary structures

Extension of the plasma radiation database PARADE for the analysis of meteor spectra

The advancement in the acquisition of spectral data from meteors, as well as the capability to analyze meteoritic entries in ground testing facilities, requires the assessment of the performance of software tools for the simulation of spectra for different species. The Plasma Radiation Database, PARADE, is a line‐by‐line emission calculation tool. This article presents the extensions implemented for the simulation of meteor entries with the additional atomic species Na, K, Ti, V, Cr, Mn, Fe, Ca, Ni, Co, Mg, Si, and Li. These atoms are simulated and compared to ground testing spectra and to observed spectra from the CILBO observatory. The diatomic molecules AlO and TiO have now been added to the PARADE database. The molecule implementations have been compared to the results of a simple analytical program designed to approximate the vibrational band emission of diatomic molecules. AlO and TiO have been identified during the airborne observation campaigns of re‐entering man‐made objects WT1190F and CYGNUS OA6. Comparisons are provided showing reasonable agreement between observation and simulation

Spectral observations at the Canary Island Long-Baseline Observatory (CILBO): calibration and datasets

The Canary Island Long-Baseline Observatory (CILBO) is a double-station meteor camera setup located on the Canary Islands operated by ESA's Meteor Research Group since 2010. Observations of meteors are obtained in the visual wavelength band by intensified video cameras from both stations, supplemented by an intensified video camera mounted with a spectral grating at one of the locations. The cameras observe during cloudless and precipitation-free nights, and data are transferred to a main computer located at ESA/ESTEC once a day. The image frames that contain spectral information are calibrated, corrected, and finally processed into line intensity profiles. An ablation simulation, based on Bayesian statistics using a Markov chain Monte Carlo method, allows determining a parameter space, including the ablation temperatures, chemical elements, and their corresponding line intensities, to fit against the line intensity profiles of the observed meteor spectra. The algorithm is presented in this paper and one example is discussed. Several hundred spectra have been processed and made available through the Guest Archive Facility of the Planetary Science Archive of ESA. The data format and metadata are explained

Experimental Simulation of Meteorite Ablation during Earth Entry Using a Plasma Wind Tunnel

International audienceThree different types of rocks were tested in a high enthalpy air plasma flow. Two terrestrial rocks, basalt and argillite, and an ordinary chondrite, with a 10 mm diameter cylindrical shape were tested in order to observe decomposition, potential fragmentation, and spectral signature. The goal was to simulate meteoroid ablation to interpret meteor observation and compare these observations with ground based measurements. The test flow with a local mass‐specific enthalpy of 70 MJ kg(‐1) results in a surface heat flux at the meteorite fragment surface of approximately 16MW m(‐2). The stagnation pressure is 24 hPa, which corresponds to a flight condition in the upper atmosphere around 80 km assuming an entry velocity of 10 km s(‐1). Five different diagnostic methods were applied simultaneously to characterize the meteorite fragmentation and destruction in the ground test: short exposure photography, regular video, high‐speed imaging with 10 kHz frame rate, thermography, and Echelle emission spectroscopy. This is the first time that comprehensive testing of various meteorite fragments under the same flow condition was conducted. The data sets indeed show typical meteorite ablation behavior. The cylindrically shaped fragments melt and evaporate within about 4 s. The spectral data allow the identification of the material from the spectra which is of particular importance for future spectroscopic meteor observations. For the tested ordinary chondrite sample a comparison to an observed meteor spectra shows good agreement. The present data show that this testing methodology reproduces the ablation phenomena of meteoritic material alongside the corresponding spectral signatures

Assessment of high enthalpy flow conditions for re‐entry aerothermodynamics in the plasma wind tunnel facilities at IRS

This article presents the full operational experimental capabilities of the plasma wind tunnel facilities at the Institute of Space Systems at the University of Stuttgart. The simulation of the aerothermodynamic environment experienced by vehicles entering the atmosphere of Earth is attempted using three different facilities. Utilizing the three different facilities, the recent improvements enable a unique range of flow conditions in relation to other known facilities. Recent performance optimisations are highlighted in this article. Based on the experimental conditions demonstrated a corresponding fight scenario is derived using a ground-to-fight extrapolation approach based on local mass-specific enthalpy, total pressure and boundary layer edge velocity gradient. This shows that the three facilities cover the challenging parts of the aerothermodynamics along the entry trajectory from Low Earth Orbit. Furthermore, the more challenging conditions arising during interplanetary return at altitudes above 70 km are as well covered