N _2 -H _2 discharges are systematically studied using a coaxial dielectric barrier discharge reactor for ammonia synthesis by means of mass spectrometry, electrical characterization and high-resolution emission spectroscopy. The influence of packing is investigated by accommodating chemically inert SiO _2 beads in the discharge volume from 920 to 13 mbar. Above 275 mbar, the discharge is dominated by filaments associated with intense microdischarges, whereas at lower pressures, the plasma becomes diffuse and occupies a large volume. In presence of packing, the intensity of the microdischarges at 920 mbar are strongly suppressed, while the electrical and emission properties of the diffuse plasma remain largely unaffected. The absence of intense microdischarges in the diffuse mode at low pressures eliminates important NH _3 dissociation channels. Decreasing the pressure below 100 mbar leads to a significant increase in [NH _3 ] with SiO _2 beads. This is attributed to both an increase of E/n, which favours H _2 and N _2 dissociation, and consequently to an increase in plasma-surface reactions involving H and N towards ammonia formation. Investigations at 50 mbar reveal that introducing SiO _2 beads in contact with the plasma has a more limited impact on [NH _3 ] than at 920 mbar. The emission spectra are dominated by the second positive system of N _2 , first negative system of N _2^+ , and H _α , with no evidence of excited NH ^* . The rotational temperature of N _2 (C) is mostly affected by [N _2 ] in [H _2 ] in the empty reactor at 920 mbar, reaching about 808 K at 75 vol. _2 . With packing or at 50 mbar the rotational temperature remains at ≈ 400 K. For all tested conditions, the vibrational temperatures of N _2 (C) lie in the range of 3500-3900 K .

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 19.6kWh 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 29h 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.

A diagnostic setup for one-dimensionally spatially resolved two-photon absorption laser-induced fluorescence (TALIF) detection of ground state oxygen atoms ( 2 p 4 3 P 2 , 1 , 0 ) is developed. The goal of this study is to investigate the evolution of temperatures and absolute number densities of oxygen atoms along the effluent of a low-pressure CO2 microwave discharge in order to gain insights into some of the mechanisms governing the post-discharge regime. The plasma source is operated at conditions of 600 W- 1200 W of absorbed power with flow rates of 74 sccm and 370 sccm pure CO2 at pressures between 1.2 mbar and 5 mbar with specific energy inputs up to 111.9 eV/molecule. These operating conditions exhibit high CO2 conversions (up to 90%) at low energy efficiencies (2%-7.4%), due to direct electron impact dissociation driving the conversion process resulting in splitting of CO2 into CO and metastable oxygen atoms. The TALIF measurements yield spatially resolved translational temperatures between 1000 K- 1600 K for most operating conditions and axial positions along the effluent. Reference measurements with xenon 6 p ' [ 3 / 2 ] 2 are used for absolute number density calibration. The resulting axially resolved number density profiles of ground state atomic oxygen increase along the effluent, even at considerable distances of several centimeters from the active discharge, before they reach a maximum between 5 x 10 20 m-3 and 2.2 x 10 21 m-3 depending on the condition, and decrease after that. This behavior indicates the potential significance of quenching of metastable oxygen atoms within the post-discharge regime of the investigated CO2 discharges. The measured spatially resolved number density evolutions are qualitatively consistent with quenching via wall collisions being the dominant deactivation mechanism, underlining the importance of particle-wall interactions.

The removal of oxygen from the effluent of a CO2 plasma using multiple perovskite La0.6Ca0.4Co0.5Fe0.5 O3-delta hollow fiber membranes is reported. A microwave plasma torch featuring a water-cooled 5 mm nozzle operated at quasi-atmospheric pressure was used. This configuration yielded moderate CO2 conversions (>= 20%) and sufficiently large temperatures to thermally activate up to 21 membranes distributed over various rows in the plasma effluent. The CO2 conversion was only slightly affected by the microwave power and remained unchanged, regardless of the number of membranes placed in the effluent. The amount of permeated oxygen increased both with the microwave power and with the number of membranes, since the former yields hotter effluents (>700 degrees C) and the latter increases the surface area available for permeation. The largest O-2 permeation flow was obtained for 21 membranes and a microwave power of 2550 W: similar or equal to 42 sccm or similar or equal to 4.8% of the available O-2. These correspond to the highest performances of such a plasma-membrane reactor thus far. The permeated O-2 flow was also affected by the argon flow purging the membranes. Using one membrane, the flow of extracted oxygen decreased for an Ar flow below 250 sccm, while the opposite was observed with 10 membranes, yielding an increase in the oxygen flow from similar or equal to 25 to similar or equal to 28 sccm upon decreasing the total Ar flow below 2500 sccm. Key aspects that must be tackled for the design and testing of a plasma-membrane prototype that aims to remove O-2 beyond 90% are discussed.

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.

Improvement of the CO2 conversion using a 2.45 GHz microwave plasma torch in reverse vortex configuration with cooled effluent channels at atmospheric pressure is reported. This configuration allows for fast gas quenching by efficient gas cooling of the effluent, which leads to conversion and energy efficiency results at 900 mbar that are very similar to the highest conversion and energy efficiency values typically obtained at lower pressures (100-200 mbar). The convective cooling in long cooled channels proved to be effective, particularly in the configuration with multiple channels, where the effective cooling surface was increased by a factor of 2.4. In comparison with the forward vortex the reverse configuration did not improve conversion, it did improve plasma stability, demonstrating that the observed effect can be attributed to the convective gas cooling in the effluent by gas-surface interaction. High specific energy inputs (> 5.5 eV/ molecule) were achieved in experiments where narrow gas inlets were used, resulting in 8 times higher inlet CO2 velocities that stabilised the plasma, allowing conversion values up to 57% at 900 mbar. The plasma stabilisation was most effective at low flow rates, where high gas velocity confined the plasma to the quartz tube centre and allowed coupling higher power to the plasma (high SEI). Additionally, experiments without a vacuum pump at atmospheric pressure were performed, yielding identical results as at 900 mbar, demonstrating that the vacuum pump is not needed to achieve high conversion rates with the use of the reverse vortex configuration with cooled effluent channels.

Measurements of the radiative heat flux component contributing to the total stagnation point heat transfer rate in high-enthalpy ground testing facilities are assessed in this paper. The new idea to measure the radiative contribution is the removal of the convective heating by gas injection into the stagnation region. This leaves only radiative heat transfer, which is measured using a classical water calorimeter. Using gas specific absorption the VUV radiation can be separated. The approach compares well to radiometric sensor data for one flow condition. In total, four conditions are investigated and the measured VUV radiative heating amounts to 0.74 % up to 5.8 %of the total incident heat flux.

Spallation is the mostly undesirable phenomenon where solid particles are ejected from ablative materials leaving less mass to be decomposed at the ablator surface. The exact mechanisms and conditions that promote spallation as well as the extent of it are unclear to this date. This paper presents the results of an extensive test campaign targeted at measuring spallation of carbonaceous ablator materials in an arc heated air flow of [Formula: see text]. The employed diagnostic methods are photogrammetric surface measurements, high-speed imaging, thermography, and two-color-ratio pyrometry using the raw digital single-lens reflex camera images from the photogrammetry setup. Data from the high-speed camera show a much higher spallation rate for the carbon preform Calcarb than for carbon-phenolic ablators. Temperature measurements show a difference of up to 300 K between carbon fibers and surrounding matrix. The pyrolysis gas from the phenolic resin is found to decrease the spallation rate of the carbon-phenolic ablator ZURAM compared to Calcarb, and the pyrolysis gas pressure slightly increases the distance that particles travel upstream after ejection from the front surface.

This talk will introduce the The Canary Island Long-Baseline Observatory (CILBO), a double station meteor camera setup located on the Canary Islands and operated by ESA’s Meteor Research Group since 2010. Our 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 to determine 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 talk. Several hundred spectra have been processed and will be made available through the Guest Archive Facility of the Planetary Science Archive of ESA.

View Video Presentation: https://doi.org/10.2514/6.2022-0264.vid An approach for the experimental simulation of entry conditions into the atmosphere of gas giant Neptune is presented. The PWK1 facility at the Institute of Space Systems of the University of Stuttgart has been modified in order to be used with hydrogen-helium mixtures. Additionally, methane was injected aiming at investigating the influence of methane on the radiation behavior. Methane could significantly change the radiative heating behavior during the entry flight. Based on first emission spectroscopic measurements, it is shown that methane influences the spectra behavior considerably. CH and C2 moleular radiation appear and the overall radiation level is higher. The prominent hydrogen Balmer series are saturating the spectrometer, which needs further attention in future measurements.

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.

Spallation is the undesirable phenomenon where solid particles are ejected from ablative materials without the endothermic decomposition on the ablator surface. In this paper, three non-intrusive diagnostic methods are presented, which allow the experimental quantification of spallation. The motivation is that the exact mechanisms and conditions that promote spallation as well as the extent of it are unclear to this date. This paper presents the first results of an extensive test campaign targeted at measuring spallation of carbonaceous ablator materials in an arc heated air flow of 70 MJ/ kg. The employed diagnostic methods are photogrammetric surface measurements, high-speed imaging and thermography. Data from the high speed camera shows a much higher spallation rate for the carbon preform Calcarb than for carbonphenolic ablators. Temperature measurements showa difference of up to 300Kbetween carbon fibers and surrounding matrix.

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.

This article demonstrates the feasibility of polarization spectroscopy as a diagnostic tool for quantitative analysis of atmospheric pressure plasma conditions. Atmospheric pressure air and CO2 plasma flows created in a microwave-powered plasma torch are investigated. A detailed line-by-line simulation approach is employed to interpret the polarization spectra recorded in the resonator of the plasma torch. The line-by-line code for the simulation of polarization spectroscopy of O2 Schumann–Runge has been developed and verified with measurements in atmospheric pressure O2 plasma for a previous study. In this study, this simulation code for O2 absorption is used to model the polarization spectra measured in CO2 plasma and determine the inner energy distribution of the molecules for the first time. The resulting vibrational and rotational temperatures are Tvib=6115K and Trot=2660K. In order to simulate measurements in air plasma, the line-by-line code is extended to enable two-species modeling using O2 Schumann–Runge as well as NOγ absorption. The new two-species simulation approach allows for the determination of the relative number density nO2/nNO=1500±100. This paper clearly demonstrates the value of polarization spectroscopy as a quantitative measurement technique for atmospheric pressure plasma applications.

We demonstrated the capability of the updated Canary Island Long Baseline Observatory (CILBO) meteor detection system to measure relative elements intensities of meteors. Meteor spectra provide valuable information on the chemical properties of individual meteoroids. In some cases, this may be the only information on the chemical composition of the parent bodies, and on transforming processes that occur during the meteoroid's journey from its source to Earth. The CILBO spectroscopic program has been created with the intention of carrying out regular systematic spectroscopic observations. At the same time, the meteoroid trajectory and pre-atmospheric orbit are independently measured from data collected by the other cameras in the network. We presented the meteor spectroscopy pipeline developed by the Meteor Research Group of the European Space Agency, and it's application to the spectroscopic survey of Geminid meteor shower observed by CILBO.

Polarization spectroscopy measurements of O-2 B-3 Sigma(-)(u) <- X-3 Sigma(-)(g) Schumann-Runge absorption are pre- sented. The measurements are carried out in the resonator of a microwave-powered plasma torch operated with O-2 at atmospheric pressure. A line-by-line spectral simulation code is developed in order to validate the measured spectra at the expected translational, rotational, and vibrational temperatures T-trans = T-rot = 3000 K and T-vib = 7000 K. The results show very good agreement with the spectral features of the measured O-2 polarization spectra. The range of probed vibrational and rotational transitions confirms the feasibility of polarization spectroscopy as a quantitative diagnostic tool for various applications. (C) 2020 Elsevier Ltd. All rights reserved.

In this study, the applicability of polarization spectroscopy to the detection ofO2 in atmospheric pressure CO2 plasma is investigated. Reference measurements in O2 plasma are used to verify the detected polarization spectra of O2 B 3Sigma - X 3Sigma Schumann-Runge. First results from a new line-by-line spectral simulation code for polarization spectroscopy of O2 are presented. The measured spectra allowthe identification of 13 rotational lines from 12 different vibrational branches within a narrow spectral range. The temperatures of the best fit are Trot = Ttrans = 6212:5Kand Tvib = Telec = 10000 K. These temperatures seem high for the investigated plasma facility. However, the potential of polarization spectroscopy as a viable tool for high-resolution measurements of O2 Schumann-Runge absorption in atmospheric pressure plasmas is shown.

O2 plasma created in a microwave powered plasma torch at atmospheric pressure is investigated. Measurements of electronic excitation temperature and relative groundstate density of atomic oxygen are carried out using optical emission spectroscopy and two-photon induced polarization spectroscopy respectively. The results presented in this paper indicate that the gas temperature is largely independent of the microwave power. Changes to the microwave power manifest as variations of the plasma volume which is observed as a drop in relative atomic oxygen number density. These findings are in agreement with previous investigations with other plasma species at similar conditions.

Transpiration cooling is an active thermal protection system (TPS), in which a coolant gas is fed through a porous material. This requires a material that stays structurally stable at high temperatures, while having the desired permeability. This paper explores transpiration cooling of Ultra-High-Temperature-Ceramics (UHTCs). A stagnation probe with transpiration cooled ZrB2 was tested in a plasma wind tunnel at a null point heat ux of 3.59 MW/m2 in steady state and transiently at 2 MW/m2. The aim is to understand whether transpiration cooling can increase the UHTC operating temperature by shielding it from oxygen and reducing the heating from surface re-combination. Several diagnostics are applied, including an Echelle spectrograph that explores outgassing of oxidation products from the surface. Infrared thermography is employed to track the surface temperature at the front and the back surface temperature is measured by a pyrometer. Furthermore, the Planck radiation background of the emission spectra is used to assess the front surface temperature. The testing included a variation in the injectant species and mass ux. While the uncooled sample fully oxidised at a surface temperature of 2150 K, 20.25 g/m2s of helium and 620.11 g/m2s of nitrogen prevented oxidation of the transpiration cooled samples. At a blowing parameter of 0.1094, the helium cooled probe reached a front surface temperature of 1428 K and reduced the incident heat ux by 77 % compared to the uncooled sample. The nitrogen cooled sample had a maximum front surface temperature of 1128 K with a blowing parameter of 1.958 and an 83.3 % lower incident heat ux than the uncooled sample.