Sébastien Dozias

Study of pulsed neon–xenon VUV radiating low pressure plasmas for mercury free fluorescent sign optimization

This work deals with the study and optimization of mercury free fluorescent discharge tubes for publicity lighting applications. The experimental set-up allows for time resolved spectroscopy from 110 up to 900 nm, photometric characterization in a large volume integrating sphere and the current and voltage measurement of microsecond duration signals delivered by lab-developed pulsed drivers. The glow and afterglow radiative process analysis indicates that the best performance measured with the pulsed excitation of rare gas plasma, in comparison with the conventional ac excitation, essentially originates from the efficient plasma relaxation during the afterglow at the benefit of the vacuum ultraviolet (VUV) resonance line radiated at 146.9 nm for xenon. The fit of the VUV time resolved experimental measurements, with the results issued from a simplified kinetic model of neon–xenon plasmas, evidences the crucial role of production of molecular ions during the glow phase and of their radiative recombination during the afterglow. The pulse duration and the gas mixture pressure appear as two experimental parameters whose influence, studied over an extended range, has been demonstrated to bring about a significant sign performance enhancement. There exists an optimum pulse duration range, which results in the appearance of limited stepwise excitation and ionization processes, favourable for an intense afterglow VUV production. The pressure dependence study shows that the best performance for pulsed excitation is obtained in Ne/Xe (100/1) mixtures around 50 mbar, at the difference of an ac driven Ne/Xe plasma for which the best conditions were reported to be of a few millibars. This pressure increase results both in the VUV and sign light output enhancement and the successful continuous operation of pulsed mercury free signs for time as long as 4000 h with neither electrode erosion, nor glass or phosphor degradation nor chromatic coordinate variation. For the green phosphor covered, 65 cm long and 13 mm inner diameter signs, the efficiency of a pulsed neon–xenon discharge likely to be operated for a few thousand hours reaches 50% of that of the same tube filled with mercury based mixtures.

Abstract 2839: Antitumor activity on colorectal and pancreatic tumors of a new strategy based on ROS generation by non-thermal plasma

Background. Local treatments of tumors are mainly based on surgical resection and/or treatment such as photodynamic therapy (PDT) or ionizing radiation (IR). Action mechanisms of IR and PDT are based on the generation of ROS in the vicinity of the cells. In this context, cold or Non Thermal Plasma (NTP), a new technology which can generate in situ ROS, is currently under investigations. NTP is a cold ( Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2839. doi:1538-7445.AM2012-2839

Soft X-ray diagnostics of density and dynamics of dodecane sprays

The optimization of vehicle engine injectors has been and is still today a critical issue for the reduction of fuel consumption, the limitation of air pollutant release and the development of alternative fuels. An extended panel of diagnostic techniques is applied for the spray atomisation description in connection with a large effort in modelling works. Dealing with the near nozzle region, i.e. the dense region of the spray, only the X-ray absorption technique was shown to be able to provide valuable data. Very significant improvement of this high density region characterization was recently achieved using unique features of synchrotron X-rays1.

Characterization and optimization of a flash X-ray source for dense spray radiography

Summary form only given. Liquid sprays analysis, as those generated by fuel injection systems, implies diagnosis procedures able to produce information for matter in different phases from liquid to vapor. The high speed sprays produced by the fuel injection systems, need a fast and reliable diagnosis technology. Previous works on N2 cryogenic jets in a high pressure chamber had shown that the use of flash X-ray system can provide valuable data over wide range of parameter conditions. The flash X-ray (called DIKEV), is a transportable blumlein table top source build at GREMI laboratory to perform radiography of fuel injection sprays. This device delivers high X-ray doses, a few mGy per pulse at the output window, in pulses of tens of nanoseconds duration and operates from single shot up to 50 Hz repetition rate. DIKEV efficiency optimized for charging voltage ranging from 10 to 25 kV, leads to the production of X-ray photons with energy ranging from 5 to 40 keV. The low part of this photon energy range, where most photon are produced , is matched for the radiography of dense spray of light elements. The X-ray focus size is not controlled by electrostatic grids as in case of conventional X-ray tubes, but is correlated with the pulsed electric field topography in the X-ray diode. A significant reduction of the X-ray focus size was achieved. This have been possible thanks to the high efficiency of the carbon fiber as field emitter cathode; which permitted an important reduction of cathode size (graphite rods of diameter ranging from 0.5 mm to 2 mm and 10 mum carbon fiber) without dose reduction up to 1000 shots. The density calculation from Beer Lamberts law, requires the precise knowledge of X-ray spectrum. For four different metallic anodes, a DIKEV full spectra characterization has been made with a germanium photodetector. The most important K,L characteristics lines below 30 keV for each anode were identified together with Bremsstrahlung spectra. In contrast to Mo case where continuum spectrum is dominant, a very high, characteristic line to Bremsstrahlung ratio was measured for Cu anode. Best anode material can be easily selected to be adapted to given spray characteristics.

Energetic Photons From Transient Plasma Discharges

An overview of the plasma based sources of energetic photons, ranging from UV to hard X‐rays, developed in GREMI is proposed. Each source principle is shortly described and applications of these specially designed sources are documented. The possibility of producing energetic photons over a very broad wavelength domain, together with the versatility of the mode of operations allow for a very large range of applications. The matching of the photon energy, the pulse repetition rate, the short duration, of a few nanosecond, of photon pulses offer for instance unique possibility for fast dynamic study, low Z element spray characterization, X‐ray fluorescence of dense targets, lithography issues, and UV VUV radiating plasma optimization.