Time-resolved spectroscopy of high pressure rare gases excited by an energetic flash X-ray source

International audienceFluorescence from high pressure (0.1-30 bar) rare gas plasmas has been excited using an intense flash X-ray source specially developed and optimized for this experiment. Spectral analysis of the so-called “third continuum” of rare gases is presented. Time-resolved spectroscopy, absorption measurements and pressure dependence studies have provided an extended database on this longer wavelength continuum of rare gases. These data allow us to understand some of the previously contradictory results reported in the literature. They strongly support a multi-component spectral aspect of the previously called “third continuum”. In fact, the observed fluorescence result from the superposition of several continua whose relative intensities are strongly dependent upon pressure. This suggests that different species are at its origin. The name of “third continuum” does not seem anymore appropriate when speaking of the whole fluorescence emitted in the longer wavelength continuum by high pressure rare gas plasmas. Generally speaking, the flash X-ray device was proven to be a very convenient and powerful tool for the study of high pressure plasmas resulting in UV-VUV fluorescence

Modeling of high-pressure rare gas plasmas excited by an energetic flash X-ray source

International audienceIn this paper, a comprehensive description of the kinetics of argon plasmas has been formulated for atmospheric pressures. It has been used to attribute to molecular species the ultraviolet-vacuum ultraviolet (UV-VUV) continua, observed between 150 and 300 nm in pure argon. The participation of both ionic dimers and trimers has been found to be necessary to explain the whole fluorescence emitted by the rare gases (Rg). A simple kinetic model of high-pressure (1-30 bar) argon plasmas created by flash X-ray excitation is reported. The photoexcitation of Rg at high pressure by X-ray photons with energy of about 10 keV is shown to produce plasmas with significant density gradients of ionic and excited species. Spatial analysis of the energy position along the X-ray penetration path is performed in order to account for these concentration gradients. The calculation of electron density in different Rg (Ar, Kr, Xe) excited by X-ray photons of various energies (0.2-10 keV) is also reported. From these results, it appears that hash X-ray excitation of Rg can be a very interesting means to produce high-electron-density plasmas designed to selectively emit intense fluorescence in the UV-VUV spectral domai

Compact flash X-ray sources and their applications

International audienceCompact flash X-ray machines are opening up extended fields of applications. X-ray diodes driven by repetitive small size pulsers have been shown able to deliver high dose rates of X-rays in pulses of nanosecond to microsecond duration. Improvements have been carried out on the lifetime of the diodes and reliability of the systems to allow operation at constant emitted dose over long periods of time. After a brief review of recent developments, described here, in more details, is the progress obtained at the GREMI laboratory in the development of true table-top flash X-ray sources producing strong X-ray doses in nanosecond pulses at a high repetition rate (50 Hz). Doses up to 2 R (5.2 X 10-4 C/kg), measured at the output window, of X-rays between 5 and 200 keV can be generated from either a linear source (up to IO cm long) or from a focal spot of less than 300 pm in diameter depending on the electrode configuration. Of the numerous applications of compact flash X-ray sources, an example is given of the use of these devices for the excitation of high pressure gas samples, realized at GREMI. Such an energetic excitation leads to important populations of highly excited ionic species

Random lasing correlated with structural properties of ZnO thin films grown by pulsed-laser deposition

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Caractérisation d'une décharge rapide dans Hg pur.

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Diagnostique de sprays diesel par radiographie X

National audienceLe travail présente la mise en œuvre d’un diagnostic à base de rayons X vers 8 keV pour la caractérisation spatiale et temporelle dans la zone proche orifice, c’est-à-dire la région la plus dense, de sprays de diesel issus d’injecteur de série. Les principales propriétés de la source flash X sont décrites, domaine d’énergie, résolution spatiale, et géométrie de l’expérience de radiographie. Le principe et la précision de la mesure de densité des jets de carburant sont validés sur des objets tests. Les mesures traduisent l’existence de deux zones de densités et vitesse de propagation différentes sur les premières centaines de micromètre en aval de l’injecteur ainsi qu’un mélange relativement important du carburant liquide avec l’atmosphère gazeuse dans la chambre d’injection

Cinétique d'un plasma de néon-xénon pour le développement de lampes sans mercure

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Parametric study of the performance of Hg free fluorescent signs

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