Oxygen Number Density Research Articles

Oxygen and Air Density Retrieval Method for Single-Band Stellar Occultation Measurement

The stellar occultation technique is capable of atmospheric trace gas detection using the molecule absorption characteristics of the stellar spectra. In this paper, the non-iterative and iterative retrieval methods for oxygen and air density detection by stellar occultation are investigated. For the single-band average transmission data in the oxygen 761 nm A-band, an onion-peeling algorithm is used to calculate the effective optical depth of each atmospheric layer, and then the optical depth is used to retrieve the oxygen number density. The iteration method introduces atmospheric hydrostatic equilibrium and the ideal gas equation of state, and it achieves a more accurate retrieval of the air density under the condition of a priori temperature deviation. Finally, this paper analyzes the double solution problem in the iteration process and the ideas to improve the problem. This paper provides a theoretical basis for the development of a new type of atmospheric density detection method.

Nitric Oxide Concentration: A New Data Set Derived From SABER Measurements

AbstractVertical profiles of nitric oxide (NO) concentration are derived between 120 and 250 km using updated NO emission rates measured by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar (MSIS) 2.1 model is used to provide the required parameters of temperature, atomic oxygen number density, and molecule oxygen number density needed to derive the NO concentrations using a non‐local thermodynamic equilibrium (non‐LTE) model. The SABER NO concentration shows a significant correlation with solar activity with larger peak NO concentrations and higher altitude extent during solar maximum years compared to those during the solar minimum years. The SABER NO agrees well with the MSIS 2.1 NO at altitudes above 120 km for all latitudes, while the pronounced SABER‐MSIS NO discrepancy below 120 km is likely due to the temperature underestimation by MSIS 2.1. A detailed error analysis is presented and considers systematic and random errors in all the terms in the non‐LTE model used to derive the NO concentration. Random error in MSIS 2.1 temperature and atomic oxygen dominates the uncertainty in single NO profiles above 120 km. We estimated a systematic error up to ∼36% between 120 and 250 km during solar maximum years.

Removal behavior of Al–Ti–O inclusions in aluminum deoxidized molten steel containing titanium by microporous magnesium foam ceramic filters

Al–Ti–O inclusions in aluminum deoxidized and titanium (Ti)-alloyed steel aggravate the submerged nozzle clogging and instability of the continuous casting process, lowering the cleanliness of casting billet. In the present investigation, the removal behavior of the oxide inclusions in aluminum deoxidized IF steel and Ti-alloyed welding wire steel by microporous/fused MgO foam ceramic filter (PMF/FMF) and the improvement of the steel cleanliness were comparatively investigated. It is found that MgO foam ceramic filters immersed in Al deoxidized steel effectively reduced its number density of Al2O3 inclusions and total oxygen (TO) content, by use of forming Al–Mg–O spinel interface reaction layer between the filters and tested steel. Furthermore, the cleanliness increase of Ti-alloyed steel immersed by the filters, due to formation of a more complete and continuous Al–Mg–Ti–O spinel layer on their surface, was bigger compared with that in Ti-free steel, with sporadically distributed Al–Mg–O spinel of interface layer on the surface of filters immersed in Ti-free steel. This is ascribed to the higher Ti content and some liquid inclusion of MgO–Al2O3-TiOX in Ti-alloyed steel, enhancing the reaction of the MgO of aggregates in the filters with Al, Ti, and O and deposition of other solid MgO–Al2O3-TiOX on the surface of the filter, respectively. In addition, the better purification efficiency of the PMF on tested steel compared with the FMF, was due to its higher porosity, roughness and more liquid phase components of the matrix in PMF, which improve the reaction of filter with liquid steel, and raise its adsorption capacity with Al2O3-based inclusions in the steel, forming Al–Mg–O spinel interface layer to removal the oxide inclusions.

Spectral insight into the interface evolution of a carbon/carbon composite under high-enthalpy, nonequilibrium flow

Gas–surface interactions between thermal protection materials and high-enthalpy nonequilibrium flow are one of the greatest challenges in accurately predicting aerodynamic heating during supersonic flights. Finer microscopic details of flow properties are required for elaborate simulation of these interactions. Spectral insight, with quantum-state-specific characteristics, is provided in this work to investigate the physico-chemical processes in high temperature interface of a carbon/carbon (C/C) composite. The nonequilibrium air flow is produced by a 1.2 MW inductively coupled plasma wind tunnel at an enthalpy of 20.08 MJ/kg. The duration of each test is up to 100 s, and quartz is also tested for comparison. Spectral insights into the reaction mechanisms of the gas–surface interactions are acquired by the optical emission spectroscopy and laser absorption spectroscopy. Dynamic evolution of the chemical reaction pathways and thermal nonequilibrium are discussed based on the results of optical emission spectroscopy. Temporally and spatially resolved results of the translational temperature and number density of atomic oxygen are quantified by laser absorption spectroscopy. Controlling mechanisms in the surface chemistry are further analyzed in conjunction with the surface temperature, scanning electron microscopy, and energy dispersive spectroscopy. Reaction mechanisms on the C/C composite surface sequentially experience an oxidation-dominant, an intense competitive, a nitridation-dominant, and a recession dominant period. Distributions in the axial direction and dynamic characteristics of the translational temperature and number density of atomic oxygen are found closely related with surface swelling, recession, and chemical reactions. The results herein are consistent with each other and are instructive to further investigate the interface evolution on C/C composites.

Comparison and Analysis of Stellar Occultation Simulation Results and SABER-Satellite-Measured Data in Near Space

In this study, we analyze the accuracy of the stellar occultation technique to detect the oxygen number density and temperature in near space. Based on the validation of the algorithm related to stellar occultation using a single wavelength of 762 nm, the simulation and inversion are performed using the oxygen absorption A-band, and the results are compared with SABER observations to calculate the deviation. Then, the distribution of the detection accuracy with wavelength, latitude, and altitude is analyzed. The results show that the radiant transmittance of the basic observation varies significantly with wavelength and altitude, and it is not sensitive to a change of latitude. The inversion results of each wavelength at different latitudes can be combined, and it can be seen that the 754–769 nm band is preferred for oxygen and temperature detection. Therefore, analyzing the accuracy results of the specific wavelength 757.84 nm at different latitudes, the temperature accuracy can reach 0.1 K in the stratosphere at both low and high latitudes and 0.6–34 K at middle latitudes. The temperature detection accuracy in the mesosphere at each latitude reaches about a dozen K. The deviation of the inversion results at middle latitudes is larger in the thermosphere, and at the other two latitudes, it is about a few dozen K. From the analysis of relative deviation, excluding the deviation of 95–100 km, the deviation of other altitudes is within the ideal range, and the minimum can reach 0. The accuracy of the oxygen number density increases with latitude, and the relative deviation of the middle and high latitudes is around 10–20%. Based on the above results, it is concluded that the technique of starlight occultation exhibits high accuracy for detecting atmospheric parameters in the near space region, and the results lay the technical foundation for the independent development of stellar occultation.

Gas–surface interactions in a large-scale inductively coupled plasma wind tunnel investigated by emission/absorption spectroscopy

Precise prediction of aerothermal loads is significantly limited by the unclear interactions between the thermal protection system surface and the surrounding high-enthalpy gas. To address this, we propose an optical diagnostic method based on optical emission spectroscopy and laser absorption spectroscopy to investigate the gas–surface interactions within the boundary layer. Experiments are conducted in an air plasma flow produced by the 1.2 MW inductively coupled plasma wind tunnel at the China Academy of Aerospace Aerodynamics with an enthalpy of 20 MJ/kg and a heating time of 100 s. The cylindrical samples made of pure silicon carbide are tested, and quartz samples with the same exposed geometry are tested in parallel as a reference material. The optical emission spectroscopy system has four spectrometers to cover the wide wavelength range of 200–1100 nm, providing qualitative, spatially, and spectrally resolved measurements of the multi-species radiative emission adjacent to the sample surface. Laser absorption spectroscopy is deployed at different axial locations to quantify the number density and translational temperature of OI (3s5S) with a 500 Hz scanning rate and 200 kHz acquisition rate. Additionally, the surface temperature of each sample is detected by an infrared pyrometer. Scanning electron microscopy and energy dispersive spectrometry are performed before and after the plasma heating. Our measurement results provide valuable information on surface reaction pathways and catalytic recombination effects on atomic oxygen number density distributions. Finally, these self-consistent results show that the proposed method is reliable to deeply investigate gas–surface interactions within boundary layer in harsh aerothermal environment.

An optimal estimation-based retrieval of upper atmospheric oxygen airglow and temperature from SCIAMACHY limb observations

Abstract. An optimal estimation-based algorithm is developed to retrieve the number density of excited oxygen (O2) molecules that generate airglow emissions near 0.76 µm (b1Σg+ or A band) and 1.27 µm (a1Δg or 1Δ band) in the upper atmosphere. Both oxygen bands are important for the remote sensing of greenhouse gases. The algorithm is applied to the limb spectra observed by the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument in both the nominal (tangent heights below ∼ 90 km) and mesosphere–lower thermosphere (MLT) modes (tangent heights spanning 50–150 km). The number densities of emitting O2 in the a1Δg band are retrieved in an altitude range of 25–100 km near-daily in 2010, providing a climatology of O2 a1Δg-band airglow emission. This climatology will help disentangle the airglow from backscattered light in nadir remote sensing of the a1Δg band. The global monthly distributions of the vertical column density of emitting O2 in a1Δg state show mainly latitudinal dependence without other discernible geographical patterns. Temperature profiles are retrieved simultaneously from the spectral shapes of the a1Δg-band airglow emission in the nominal limb mode (valid altitude range of 40–100 km) and from both a1Δg- and b1Σg+-band airglow emissions in the MLT mode (valid range of 60–105 km). The temperature retrievals from both airglow bands are consistent internally and in agreement with independent observations from the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), with the absolute mean bias near or below 5 K and root mean squared error (RMSE) near or below 10 K. The retrieved emitting O2 number density and temperature provide a unique dataset for the remote sensing of greenhouse gases and constraining the chemical and physical processes in the upper atmosphere.

A Simulation Study on the Variation of Thermospheric O/N2 With Solar Activity

AbstractThe ratio of number density of atomic oxygen (O) to that of molecular nitrogen (N2) in the thermosphere (O/N2) on the constant pressure surface, which has complex temporal and spatial characteristics, is widely regarded as an important parameter connecting the terrestrial thermosphere and daytime ionosphere. Previous studies demonstrated that the thermospheric O/N2 increases with increasing solar activity, and the changes in O/N2 with solar activity show significant difference between winter and summer hemispheres. However, the root causes, which are responsible for the solar activity variation of O/N2, are not fully understood. In this study, the contributions of various physical and chemical processes on the response of O/N2 to the solar radiation change were quantitatively investigated through a series of controlled simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model. The simulation results suggested that the chemical processes lead to the increase of thermospheric O/N2 over the globe with increasing solar activity. The increase of O/N2 with solar activity is dominated by the enrichment of O abundance and the loss of N2 abundance in the lower and upper thermosphere, respectively. Moreover, the simulation results suggested that the stronger hemispheric asymmetry is attributed to the stronger thermospheric circulation, which changes the vertical advection of O/N2 through both direct and indirect effects.

Analysis of inversion error characteristics of stellar occultation simulation data

Atmospheric stellar occultation observation technology is an advanced space-based detection technology that can measure the vertical distribution of trace gas composition, temperature, and aerosol content in a planet’s atmosphere. In this study, an inversion algorithm of the onion-peeling method was constructed to invert the transmittance obtained from the forward mask. The method used a three-dimensional ray-tracing simulation to obtain the transmission path of the light in the Earth’s atmosphere. The relevant parameters were then combined in the high-resolution transmission molecular absorption (HITRAN) database, and line-by-line integration was performed to calculate the atmospheric transmittance. The transmittance value was then used as an input to calculate the vertical distribution of oxygen molecules when using the single-wavelength inversion of the onion-peeling method. Finally, the oxygen molecule content was compared with the value attained by the Mass Spectrometer and Incoherent Scatter Radar Extended (MSISE00) atmospheric model to determine the relative error of our model. The maximum error was found to be 0.3%, which is low enough to verify the reliability of our algorithm. Using Global-scale Observations of the Limb and Disk (GOLD) measured data to invert the oxygen number density, we calculated its relative deviation from the published result to further verify the algorithm. The inversion result was affected by factors such as prior data, the absorption spectral line type, the ellipticity of the Earth, and the accuracy of the orbit. Analysis of these error-influencing factors showed that the seasons and the Earth’s ellipticity affected the accuracy of the model only 0.001% and could therefore be ignored. However, latitude and solar activity had a greater impact on accuracy, on the order of 0.1%. The absorption line type affected the accuracy of the model by as much as 1%. All three of these factors therefore need to be considered during the inversion process.

Transient Change of Io's Neutral Oxygen Cloud and Plasma Torus Observed by Hisaki

AbstractIo's atmospheric oxygen atoms are heated by atmospheric sputtering and escape from Io's gravity, forming a neutral oxygen cloud around Io's orbit. This neutral cloud is important as a source of the Io oxygen plasma torus. Previous studies derived the distribution and density of the equilibrium neutral oxygen cloud. However, little is known about the evolution of the neutral cloud. In this study, we analyzed Hisaki satellite observations of the spatial distribution of OI 130.4 nm emissions around Io's orbit during transient strong density enhancement in the torus in 2015 (called high density period). Comparing time variations of OI and OII 83.4 nm emissions, we estimated that the lifetimes of O+ in this period were about 21 days in the high density period and 41 days in the normal density period. Hisaki observations are consistent with a decrease in the lifetime of O+ when the density in the torus increases. The radial distribution showed the neutral oxygen cloud spread outward up to 8.6 Jupiter radii during the high density period. We also show that during the high density period, the neutral oxygen number density at Io's orbit (where north‐south thickness is assumed to be 1.2 Jupiter radii) increased to cm−3, more than three times the value during the normal density period ( cm−3). The azimuthal distribution showed a dense region around Io and a longitudinally uniform, diffuse region distributed along Io's orbit that enlarges during the high density period.

Radiative cooling due to NO at 5.3 [formula omitted]m emission as observed by TIMED/SABER over Asian sector

The effect of geomagnetic storms on the peak emission of NO Volume Emission Rate (NO VER) at 5.3 μm, in mesosphere and lower thermosphere (MLT) region, is studied over the Asian sector during 26–29 September 2011 (storm 1) and 18–21 February 2014 (storm 2). The data for peak emission of NO VER is obtained from SABER instrument onboard the NASA’s TIMED satellite. The SABER retrieved data along with the neutral densities obtained from NRLMSISE-00 model have been used to study the latitudinal and longitudinal variation of peak NO VER during the storm period. The variations induced in the peak emission of NO VER is understood with the help of fluctuations in neutral species and the resulting changes in chemistry. It has been found that the peak emission of NO VER is strongly influenced by the storm conditions. The peak emission of NO VER at 5.3 μm is found to be maximum at higher latitudes during the storms. However, the magnitude of peak NO VER gradually decreases towards the equator during the storms. The modeled atomic oxygen number density shows depletion at the higher latitudes corresponding to peak altitude of NO VER. There is a negative correlation between the peak emission of NO VER and Dst index during the main phase of the storm. The peak emission of NO VER and modeled atomic oxygen number density shows the positive correlation at the equator region, while negative correlation at the higher latitudes. At higher latitudes modeled atomic oxygen number density shows positive correlation with Dst index, while negative correlation at the equator. The correlation factors obtained between various parameters related to the storm time radiative cooling strongly support the existing understanding of the variation of NO VER during extreme space weather events.

The formation of bimodal dust species in nova ejecta – I. Chemical conditions

Abstract It is still not known whether or not bimodal dust species (namely the silicate and amorphous carbon dust grains that are observed in a nova eruption) are formed in nova ejecta. Using the Modules for Experiments in Stellar Astrophysics code and considering the effects of the white dwarf mass, the mass-accretion rate and the chemical profile, which are described by a new parameter (the mixing depth), on the chemical abundances of nova ejecta, we investigate the possibility that bimodal dust species are produced in a nova eruption. We find that the C/O (the ratio of the carbon number density to the oxygen number density) of nova ejecta is affected by the mixing depth. For a model with a small mixing depth, the C/O of nova ejecta can evolve from greater than 1.0 to less than 1.0 over the course of an eruption, thereby providing the chemical conditions for the formation of bimodal dust species.

Atomic oxygen number densities in the mesosphere–lower thermosphere region measured by solid electrolyte sensors on WADIS-2

Abstract. Absolute profiles of atomic oxygen number densities with high vertical resolution have been determined in the mesosphere–lower thermosphere (MLT) region from in situ measurements by several rocket-borne solid electrolyte sensors. The amperometric sensors were operated in both controlled and uncontrolled modes and with various orientations on the foredeck and aft deck of the payload. Calibration was based on mass spectrometry in a molecular beam containing atomic oxygen produced in a microwave discharge. The sensor signal is proportional to the number flux onto the electrodes, and the mass flow rate in the molecular beam was additionally measured to derive this quantity from the spectrometer reading. Numerical simulations provided aerodynamic correction factors to derive the atmospheric number density of atomic oxygen from the sensor data. The flight results indicate a preferable orientation of the electrode surface perpendicular to the rocket axis. While unstable during the upleg, the density profiles measured by these sensors show an excellent agreement with the atmospheric models and photometer results during the downleg of the trajectory. The high spatial resolution of the measurements allows for the identification of small-scale variations in the atomic oxygen concentration.

Spatial Distribution of Io's Neutral Oxygen Cloud Observed by Hisaki

AbstractWe report on the spatial distribution of a neutral oxygen cloud surrounding Jupiter's moon Io and along Io's orbit observed by the Hisaki satellite. Atomic oxygen and sulfur in Io's atmosphere escape from the exosphere mainly through atmospheric sputtering. Some of the neutral atoms escape from Io's gravitational sphere and form neutral clouds around Jupiter. The extreme ultraviolet spectrograph called EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) installed on the Japan Aerospace Exploration Agency's Hisaki satellite observed the Io plasma torus continuously in 2014–2015, and we derived the spatial distribution of atomic oxygen emissions at 130.4 nm. The results show that Io's oxygen cloud is composed of two regions, namely, a dense region near Io and a diffuse region with a longitudinally homogeneous distribution along Io's orbit. The dense region mainly extends on the leading side of Io and inside of Io's orbit. The emissions spread out to 7.6 Jupiter radii (RJ). Based on Hisaki observations, we estimated the radial distribution of the atomic oxygen number density and oxygen ion source rate. The peak atomic oxygen number density is 80 cm−3, which is spread 1.2 RJ in the north‐south direction. We found more oxygen atoms inside Io's orbit than a previous study. We estimated the total oxygen ion source rate to be 410 kg/s, which is consistent with the value derived from a previous study that used a physical chemistry model based on Hisaki observations of ultraviolet emission ions in the Io plasma torus.

Two-photon absorption laser induced fluorescence measurement of atomic oxygen density in an atmospheric pressure air plasma jet

Atomic oxygen number density [O] is measured in an air atmospheric pressure plasma jet (APPJ) using two-photon absorption laser induced fluorescence (TALIF). Gas flow is fixed at 8 slpm, the RF power coupled into the plasma jet varied between 5 W and 20 W, and the resulting changes in atomic oxygen density measured. Photolysis of molecular oxygen is employed to allow in situ calibration of the TALIF system. During calibration, O2 photo-dissociation and two-photon excitation of the resulting oxygen atoms are achieved within the same laser pulse. The atomic oxygen density produced by photolysis is time varying and spatially non-uniform which needs to be corrected for to calibrate the TALIF system for measurement of atomic oxygen density in plasma. Knowledge of the laser pulse intensity I0(t), wavelength, and focal spot size allows correction factors to be determined using a rate equation model. Atomic oxygen is used for calibration and measurement, so the laser intensity can be increased outside the TALIF quadratic laser power dependence region without affecting the calibration reliability as the laser power dependence will still be the same for both. The atomic O density results obtained are not directly benchmarked against other known density measurement techniques. The results show that the plasma jet atomic oxygen content increases as the RF power coupled into the plasma increases.

A study of OI 844.6 nm dayglow emission under geomagnetic storm conditions

A comprehensive model is developed to study 844.6nm dayglow emission. The Solar2000 EUV (extreme ultraviolet) flux model, neutral atmosphere model (NRLMSISE-00) and latest available cross-sections are incorporated in this model. The present model is used to study the effects of geomagnetic storm on the 844.6nm dayglow emission at a low latitude station Tirunelveli (8.7°N, 77.8°E). Three geomagnetic storms which occurred during 23rd–27th August 2005, 13th–17th April 2006 and 1st–5th February 2008 are chosen in the present study. It is found that the volume emission rate (VER) shows a negative correlation with the Dst index for all the three geomagnetic storms. The present study also shows that the altitude of the peak emission rate does not vary with the activity of geomagnetic storm. The model predicts a positive correlation between the zenith intensity of 844.6nm dayglow emission and atomic oxygen number density. The consistency of atomic oxygen number density obtained from the NRLMSISE-00 model during a geomagnetic storm is checked using the satellite measurements of Earle et al. (2013). It is found that the atomic oxygen number density given by NRLMSISE-00 model is significantly lower than the measured values. Consequently, the effect of atomic oxygen number density abundance on 844.6nm dayglow emission is further studied by treating the atomic oxygen number density as a variable parameter in the present model. An increase of more than 50% in the zenith intensity above the normal level (before the onset of the storm) is found when the atomic oxygen number density which is obtained from NRLMSISE-00 model is doubled (under the limits of measurements).

A study of 732.0 nm dayglow emission at the equator under varying atomic oxygen density conditions for equinox and solstice cases

AbstractA comprehensive model is developed to compute the volume emission rate of O+(2P) 732.0 nm dayglow emission. The modeled volume emission rates are compared with the measurements as provided by Atmosphere Explorer C satellite and Dynamics Explorer 2 spacecraft. It is found that the model explains quite well the measured emission profiles. The present model is used to study the effect of atomic oxygen abundance on the volume emission rate of 732.0 nm dayglow emission at the equator for equinox and solstice. To study the effect of atomic oxygen abundance on 732.0 nm dayglow emission, the atomic oxygen number densities obtained from the NRLMSISE‐00 model are increased (or decreased) in an increment (or decrement) of 20% and are incorporated into the model to compute volume emission rate profiles. The present study shows that the peak emission rate (PER) varies linearly below the reference level of atomic oxygen number density and does not vary linearly above the reference level of atomic oxygen number density. The atomic oxygen number density at reference level corresponds to that value which is obtained from the NRLMSISE‐00 model. It is found that the altitude of peak emission rate moves upward as the F10.7 solar index increases. On average the upward movement of altitude of PER is about 9 km for both the equinox and solstice cases. The upward movement of the altitude of peak emission rate is due to the enhancement in atomic oxygen number density with increase in F10.7 solar index.

Absolute atomic oxygen density measurements for nanosecond-pulsed atmospheric-pressure plasma jets using two-photon absorption laser-induced fluorescence spectroscopy

Nanosecond-pulsed plasma jets that are generated under ambient air conditions and free from confinement of electrodes have become of great interest in recent years due to their promising applications in medicine and dentistry. Reactive oxygen species that are generated by nanosecond-pulsed, room-temperature non-equilibrium He–O2 plasma jets among others are believed to play an important role during the bactericidal or sterilization processes. We report here absolute measurements of atomic oxygen density in a 1 mm-diameter He/(1%)O2 plasma jet at atmospheric pressure using two-photon absorption laser-induced fluorescence spectroscopy. Oxygen number density on the order of 1013 cm−3 was obtained in a 150 ns, 6 kV single-pulsed plasma jet for an axial distance up to 5 mm above the device nozzle. Temporally resolved O density measurements showed that there are two maxima, separated in time by 60–70 µs, and a total pulse duration of 260−300 µs. Electrostatic modeling indicated that there are high-electric-field regions near the nozzle exit that may be responsible for the observed temporal behavior of the O production. Both the field-distribution-based estimation of the time interval for the O number density profile and a pulse-energy-dependence study confirmed that electric-field-dependent, direct and indirect electron-induced processes play important roles for O production.

Two-Photon Absorption Laser-Induced Fluorescence Investigation of Plasmas for Mars Entry

Two-photon absorption laser-induced fluorescence measurements have been conducted to investigate atomic oxygen temperature and number density in a plasma relevant to Martian entry. The high-enthalpy plasma flow has been produced by an inductively heated plasma generator. This paper describes the experimental setup and shows the applicability of laser diagnostics to Mars-relevant plasmas. Particular emphasis is put on the use of the generated data for the numerical simulation of the aerothermal chemistry of a Martian entry. Relative fluorescence signals are calibrated by a procedure using xenon as a reference. This calibration method allows the in situ experimental determination of the instrumental broadening of the spectroscopic setup and thus an accurate temperature measurement. The acquired, highly resolved line profiles of the fluorescence signal yield a translational temperature of and a mean number density of .

Use of particle-in-cell simulations to improve the actinometry technique for determination of absolute atomic oxygen density

Actinometry is a non-invasive optical technique that can be used to quantitatively monitor atomic oxygen number densities [O] in gas discharges under certain operating conditions. However, careless application of the technique can lead to erroneous conclusions regarding the behaviour of atomic oxygen in plasma. One limitation on this technique is an accurate knowledge of the various rate constants required, which in turn is hampered by an insufficiently precise knowledge of the electron energy distribution function (EEDF) in the plasma. In this work, particle-in-cell (PIC) simulations are used to generate theoretical EEDFs. To validate a simulation the electron density ne produced by the PIC code is compared with experimental ne values measured using a hairpin probe. The PIC input parameters are adjusted to optimize agreement between the PIC and experimental ne results. This approach should in principle yield an EEDF that more accurately reflects the true EEDF in the plasma. The PIC EEDF is then used to generate rate constants for the actinometry model which should improve the accuracy of the quantitative [O] result for that particular set of plasma conditions. The actinometry [O] results are then compared with [O] results obtained using two-photon absorption laser-induced fluorescence (TALIF) to validate the approach.