Chemical kinetic and radiating species studies of Titan aerocapture entry

TITAN Aerocapture entry has been studied in collaboration with the Hypersonics Centre of the University Queensland (UQ), Australia The simulation of the experimental conditions and also the flight conditions are made using CFD coupled with chemistry libraries of which CHEMKIN. This can be compared to in-code implementation for the Earth reentry. Reduced models based on combustion data bases are taken for the reactions data set for Titan’s entry

Plasma radiation for atmospheric entry at Titan: Emission spectroscopy measurements and numerical rebuilding

Emission spectroscopy measurements on a plasma representative of Titan atmosphere composition were obtained in the Inductively Coupled Plasma wind tunnel facility (VKI-Minitorch) at the von Karman Institute in Belgium. Temperatures ranged from 3600 to 5000 K, pressure was fixed at 300 mbar, and the molar composition was 1.9% CH4 and 98.1% N2. The high-pressure plasma was produced to obtain conditions close to equilibrium. In conjunction, line-by-line calculations have been carried out to assess the reliability of two distinct sets of molecular electronic transition moments, recently released, by predicting the radiative signature of high-temperature N2-CH4 plasma. The radiative transfer problem was solved by considering the plasma plume at local thermodynamic equilibrium conditions in an axisymmetric configuration. Comparisons between the synthetic and experimental spectra demonstrated good agreement for the CN Violet and high-wavelength CN Red bands, while some discrepancies were observed for the C2 Swan bands and low-wavelength CN Red band

Uniformity study in large-area showerhead reactors

Large area plasma-enhanced chemical vapor deposition of thin films such as silicon nitride or amorphous silicon is widely used for thin film transistor fabrication in the flat panel display industry. A numerical three-dimensional model to calculate the deposition uniformity over the whole electrode surface for rf rectangular showerhead reactors powered at 13.56 MHz is presented. The simulation tool is a commercially available finite-volume software (CDF-ACE (R)) which solves the multispecies, multireaction chemistry in capacitively coupled rf plasma. In order to simplify the three-dimensional geometry,the injected gas flow distribution across the showerhead is calculated separately and introduced as volumetric source terms for the gas flow and species continuity equations. The model is applied to the particular case of silicon nitride deposition and the results are compared with uniformity profiles obtained in an industrial plasma enhanced chemical vapor deposition reactor. Perturbations due to reactor edges together with nonuniform distribution of voltage due to standing wave effect are investigated as possible sources of the inhomogeneity of the thin film. (c) 2005 American Vacuum Society

Hydrogen-dominated plasma, due to silane depletion, for microcrystalline silicon deposition

Plasma conditions for microcrystalline silicon deposition generally require a high flux of atomic hydrogen, relative to SiH alpha=0 -> 3 radicals, on the growing film. The necessary dominant partial pressure of hydrogen in the plasma is conventionally obtained by hydrogen dilution of silane in the inlet flow. However, a hydrogen-dominated plasma environment can also be obtained due to plasma depletion of the silane in the gas mixture, even up to the limit of pure silane inlet flow, provided that the silane depletion is strong enough. At first sight, it may seem surprising that the composition of a strongly depleted pure silane plasma consists principally of molecular hydrogen, without significant contribution from the partial pressure of silane radicals. The aim here is to bring some physical insight by means of a zero-dimensional, analytical plasma chemistry model. The model is appropriate for uniform large-area showerhead reactors, as shown by comparison with a three-dimensional numerical simulations. The SiH alpha densities remain very low because of their rapid diffusion and surface reactivity, contributing to film growth which is the desired scenario for efficient silane utilization. Significant SiH alpha, densities due to poor design of reactor and gas flow, on the other hand, would result in powder formation wasting silane. Conversely, hydrogen atoms are not deposited, but recombine on the film surface and reappear as molecular hydrogen in the plasma. Therefore, in the limit of extremely high si lane depletion fraction (>99.9%), the silane density falls below the low SiH alpha densities, but only the H radical can eventually reach significant concentrations in the hydrogen-dominated plasma. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3328824

The meson target stations and the high power spallation neutron source SINQ at PSI

The Paul Scherrer Institut operates two meson graphite targets, Target M and Target E, for creating the world's most intense pion and muon beams by using 590MeV protons and c.w. beam currents of up to 2.4mA (=1.4MW). The energy deposit on Target E is 20kWmA−1. The proton beam feeds also the spallation neutron source SINQ, which operates in DC mode and produces thermal and cold neutrons. The SINQ target consists of a bundle of lead filled Zircaloy tubes. In this report the continuous developments of both target facilities and their operation are presented

Plasma radiation for atmospheric entry at Titan: emission spectroscopy measurements and numerical rebuilding

Emission spectroscopy measurements on a plasma representative of Titan atmosphere composition were obtained in the Inductively Coupled Plasma wind tunnel facility (VKI-Minitorch) at the von Karman Institute in Belgium. Temperatures ranged from 3600 to 5000 K, pressure was fixed at 300 mbar, and the molar composition was 1.9% CH and 98.1% N. The high-pressure plasma was produced to obtain conditions close to equilibrium. In conjunction, line-by-line calculations have been carried out to assess the reliability of two distinct sets of molecular electronic transition moments, recently released, by predicting the radiative signature of high-temperature N-CH plasma. The radiative transfer problem was solved by considering the plasma plume at local thermodynamic equilibrium conditions in an axisymmetric configuration. Comparisons between the synthetic and experimental spectra demonstrated good agreement for the CN Violet and high-wavelength CN Red bands, while some discrepancies were observed for the C Swan bands and low-wavelength CN Red bands. Copyrigh

Mars EXPRESS observation of the PHOENIX entry: simulations, planning, results and lessons learned

International audienceNASA's PHOENIX spacecraft has successfully landed on Mars on 25 May 2008. ESA supported the event by recording signals from PHOENIX by the Mars EXPRESS spacecraft using its lander communication subsystem. Following numerical simulations of the probe entry plume emission, two Mars EXPRESS instruments, namely the High Resolution and Stereo Camera (HRSC) and the Ultraviolet and Infrared Spectrometer (SPICAM), were switched on in to observe the emission associated with the atmospheric entry. No positive detection was reported unfortunately. This article reports on the simulations, the planning, and the results. The non-detection by the UV spectrometer was due to a wrong instrument setting. Result for the camera is tentatively explained by the level of emission in the visible range. Lessons learned are given in the conclusions: the entry probe trajectory should be communicated as soon as possible to all interested parties, within the boundary conditions of confidentiality obviously. It is important to plan some redundancy to prevent incorrect instrument operations. A multi-instrument multi-spacecraft campaign should be encouraged by all means. Since detection of such faint signal is challenging, the integration time must be properly matched to the event duration. Payload operational (exclusion) rules should be discussed in an open way, to check whether the prudence of such measures is procedural or physical. The numerical simulations discussed in this paper have been focused on IR radiation in the lower density flow wake, using a DSMC/line-by-line method. These could be complemented with other numerical approaches more focused in the VUV-visible region in the high-pressure bow-shock region, using continuum Navier-Stokes fluid methods, which would yield information on the contribution to the emission spectrum from minor flow species such as CN, C2 and C