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• W2147841255 abstract "Diagnostic measurements of atomic oxygen in arc-heater plumes have been conducted by using a diode-laser absorption spectroscopy technique. Number density and translational temperature of atomic oxygen were obtained from the measured absorption line profile at 777.19 nm. As a result, in an argon-oxygen mixture plume at the total enthalpy of 9.0 MJ/kg, high number density of atomic oxygen was observed, though its electronic excitation was found under-populating. In a nitrogen-oxygen mixture plume at the total enthalpy of 19.3 MJ/kg, no absorption has been measured, though in a shock layer formed in the plume, absorption was detected and density distribution has been obtained. The measured atomic oxygen density was much lower than the value expected under equilibrium conditions. INTRODUCTION Arc-heaters/arcjets are often used for the tests of Thermal Protection Systems, TPS for reentry vehicles. However, it is very difficult to specify the exact plume conditions because it is usually in thermo-chemical nonequilibrium. In recent researches, its thermal features are gradually clarified by means of emission spectroscopy. The vibrational and rotational temperatures have been deduced from the line shape of molecular emissions. As for the chemical composition of the plume, unfortunately, available information is very limited so far, except by numerical computations. Although the heat flux to TPS would vary depending on the recombination reactions on TPS surface, neither the surface catalysis nor actual degree of dissociation are known in the tests. Therefore, measurement of chemical composition of the plume will provide useful information for TPS researches. Furthermore, the information would be useful for validation of numerical codes for high-speed reacting gas flow simulation. For the investigation of chemical composition in the plume, a quantitative and non-intrusive measurement is desired. Laser-Induced Fluorescence technique, LIF is very powerful method because it can access directly to the ground level atoms and its sensitivity is quite high.' However, it requires reference atomic density to calibrate the intensity, and is only applicable to weekly dissociated flows (<1%), otherwise, the background emission from the excited atom is too strong to get the fluorescence. * Associate Professor, Department of Advanced Energy, Member AIAA, kimiy a @k. u-tokyo.ac.jp r Graduate Student, Department of Aeronautics and Astronautics * Professor, Department of Aeronautics and Astronautics, Member AIAA Copyright © 2001 The American Institute of Aeronautics and Astronautics Inc. All right reserved. Furthermore, LIF system would be so big and expensive that it is not applicable to all the arcjet/arc-heater facilities in the world. Diode-laser absorption spectroscopy technique enables us to non-intrusively access to the absorbing atoms and molecules even in high temperature and/or high Mach number flows. Although the sensitivity of density detection is not so high as that of emission spectroscopy or LIF, it is applicable to dense and highly dissociated flows even though the plume is nearly optically thick. In this research, number density of atomic oxygen in a metastable level is measured by the diode-laser absorption spectroscopy technique. The absorption line profile is traced by modulating the laser oscillation frequency around the center absorption frequency. Number density distribution can be derived from the line-of-sight absorption measurement through Abel inversion. Translational temperature of the flow can also be deduced from the broadening of absorption line. It is relatively difficult to estimate the ground level number density from the excited level one because the first excited energy level of any atom locates far above the ground level so that the estimation is quite sensitive to the population temperature we assume. Since the diode-laser absorption measurement system is compact and portable, one can bring it to any high-temperature testing facilities in different locations. In this study, our system is applied to the facilities located at the university of Tokyo and at the Japan Ultra-high TEmperature Material research center, JUTEM, which is located 400km west of Tokyo. A convenient beam-scan technique compatible for most of test chambers is also described herein. MEASUREMENT THEORY Absorption coefficient The absorption line at 111 .19 nm is one of the strongest emission and 1 American Institute of Aeronautics and Astronautics (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. absorption lines of atomic oxygen. By measuring the absorption profile, the population density at the absorbing electronic state, which is metastable in this case, is deduced. The relationship between laser intensity 7V and absorption coefficient kv is expressed by Beer-Lambert law as," @default.
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• W2147841255 date "2001-01-08" @default.
• W2147841255 modified "2023-09-23" @default.
• W2147841255 title "Absorption measurement of atomic oxygen in arc-heater plumes" @default.
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• W2147841255 doi "https://doi.org/10.2514/6.2001-814" @default.
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