Kenji Shibusawa
(Ibaraki National College of Technology, Japan)

In general, high-temperature plasmas formed over the reentry vehicle are in nonequilibrium states. In order to estimate the radiative characteristics precisely, we must investigate the nonequilibrium plasmas more. In this study, spectroscopic measurements of low-pressure microwave-discharged nitrogen plasma were conducted in the wavelength region of 550 to 1060nm. Intense radiation from N2 first positive bands of δv=0 to δv=+4 band series and nitrogen atomic lines was observed. The experimental spectra were compared with the theoretical ones with predissociation of N2 B 3πg state through N2 5σg state and triplet splitting for the transition of 3π to 3σ state. They agreed very well with each other for δv=0 to δv=+2 band series which consisted of the lower vibrational levels of v=0 to 7, but not for the higher vibrational levels of v=8 to 12 in δv=+3 and +4 series. The experimental vibrational population on each vibrational level of N2 B 3πg state was found to be formed a non-Boltzmann distribution for the higher vibrational levels. Theoretical vibrational population distribution of N2 B 3πg state was calculated using a master equation and the vibrational nonequilibrium was investigated in detailed.

Gouji Yamada
(Department of Mechanical and Aerospace Engineering, Japan)

Characteristics of carbon dioxide plasma in a 10.5kW arc-heated wind tunnel are investigated by spectroscopic measurement. The test gases are pure CO2 and a mixture of CO2 and N2 which simulates the Martian atmosphere. Optical system is calibrated using a calibration lamp in order to obtain the absolute radiation intensity. Emission spectra from plasma flow are obtained in the wavelength range from 350 to 1000 nm along the stagnation stream line around the hemisphere model. Figure shows the example of the measured spectrum in the shock layer. Measured spectrum is mainly composed of C2Swan band system and atomic lines of O. Flow properties are determined by the spectrum fitting method from the measured spectrum in the aide of the radiation analysis code, SPRADIAN2. Spatial distributions of temperatures and species concentrations along the stagnation stream line are obtained.

Shota Niinomi
(Chiba University, Japan)

Recently, owing to the sample return missions, the interest in research on nonequilibrium flows has increased considerably. When reentry vehicles enter into the atmosphere, the surface of the vehicle is exposed to hypersonic nonequilibrium flow with strong radiative heating. Therefore, research on nonequilibrium flow behind shock wave plays significant role in designing heat shields of reentry vehicles. In this study CARS (Coherent Anti-Stokes Raman Spectroscopy) method is applied to hypervelocity shock waves in low-density air. The CARS method is one of the Raman spectroscopy techniques that employs contactless temperature diagnostics. Furthermore, in order to clarify the flow uniformity behind the hypervelocity shock wave and to inspect whether the disturbance is seen at the shock front during the CARS measurement, the total radiation distribution behind the shock wave is obtained simultaneously. Finally, the CARS signals are detected behind hypersonic shock waves with a shock speed of over 4km/s up to 7km/s. In addition, the total radiation distributions are obtained at the same experiment. The vibrational and rotational temperatures are estimated by spectral fitting method. It is found that the rotational temperature exceeds the vibrational temperature when shock wave velocity is 5km/s or more, where both temperatures remains lower than translational temperature.

Makoto Matsui
(Shizuoka University, Japan)

In developing thermal protection systems for reentry vehicles, various plasma wind tunnels such as arc-heaters, inductively coupled plasma (ICP) generators are used to simulate reentry conditions. Recently, surface catalytic effects and active/passive oxidation of TPS materials has been recognized as important issues. Then, a simple measurement system of atomic oxygen (AO) density has been desired. Currently, two photon laser induced fluorescence is almost unique technique to detect AO density in high enthalpy flows. However, this method requires not only an expensive and large laser system but also severe calibration skills using a xenon gas cell. Then, using an absorption technique, a direct detection system of atomic species including AO has been developed. Since absorption lines from the most of the atomic ground state belong to a vacuum ultra-violet region, ICP plasma containing target species is used as a VUV beam source. In this study, as a first step, influences of VUV beam characteristics such as line profiles on a sensitivity are investigated using xenon gas and a brief demonstration of the AO detection in microwave oxygen plasma will be presented.

Hiroki Takayanagi
(JAXA, Japan)

Two high enthalpy wind tunnels, a 750kW arc heated wind tunnel and a 110kW inductively coupled plasma wind tunnel, have been developed in order to simulate the entry environments of the spacecraft into the atmosphere of the earth or other planets. Two-photon laser-induced fluorescence has been applied to atomic nitrogen in the air flows for diagnostics of these facilities. The translational temperature distribution has been obtained using spectral broadening of the fluorescence profiles. The absolute atomic number density is calibrated with a reference noble gas cell and a flow reactor. Figure shows number density distribution measured in the arc heated wind tunnel with 300A, 500A, and 700A, which is compared with a CFD result. In the ICP wind tunnel, measured temperatures and number densities of atomic nitrogen by LIF are compared with the results estimated by emission spectroscopy in order to validate the LIF measurement system.

Masato Funatsu
(Gunma University, Japan)

When a spacecraft reenters the atmosphere of the Earth at a hypervelocity, an extremely strong shock wave is formed over the vehicle. Then, the vehicle is aerodynamically heated and therefore thermal protection method is required to reduce the heating. In the case of severe heating, ablation method has been often used. However, property and behaviour of ablation materials during ablation have not been understood thoroughly, yet. In our laboratory, to understand SiC-ablation properties, ablation experiments were performed systematically in high-temperature air-plasma freejets. In the previous study, measurements of ablation properties such as weight loss and weight loss rate, and surface observations of test pieces before and after ablation were mainly performed. Conclusively, weight loss rate of SiC varied with heat flux and the amount of oxidized Si attached to the test piece surface. In the present study, to understand SiC ablation more, radiation from ablating SiC were measured spectroscopically in air-plasma freejets, in addition to the measurement of weight loses and weight loss rates. Figure 1 shows experimental spectra of SiC and carbon (C) ablation. In the figure, both spectra are continuous and similar to each other. From thus results, ablation properties of SiC are discussed in detail.