Jean-Marc Bauchire

Experimental study of a DBD surface discharge for the active control of subsonic airflow

The use of plasmas, created by electric discharges, as aerodynamic actuators has been an exciting research topic for more than ten years. However, investigation of these electric discharges is still incomplete. This paper presents our contribution to the study of a DBD surface discharge. Complementary and coherent electrical, optical and aerodynamic measurements as a function of various parameters and geometries were performed. We measured the influence of the frequency and applied voltage of the discharge on the dissipated power. Experimental data yielded an empirical formula to calculate dissipated power and the energy lost in the dielectric was estimated. The plasma temperatures were also evaluated by spectroscopy emission measurements of N2 molecular bands. The velocity of the airflow induced by the DBD discharge in initially still air was measured as a function of the power dissipated in the discharge for different thicknesses and types of dielectric.

Anomalous diffusion mediated by atom deposition into a porous substrate.

Constant flux atom deposition into a porous medium is shown to generate a dense overlayer and a diffusion profile. Scaling analysis shows that the overlayer acts as a dynamic control for atomic diffusion in the porous substrate. This is modeled by generalizing the porous diffusion equation with a time-dependent diffusion coefficient equivalent to a nonlinear rescaling of time.

Molecular Dynamics simulations of clusters and thin film growth in the context of plasma sputtering deposition

Carrying out molecular Dynamics simulations is a relevant way for understanding growth phenomena at the atomic scale. Initial conditions are defined for reproducing deposition conditions of plasma sputtering experiments. Two case studies are developed for highlighting the implementation of molecular dynamics simulations in the context of plasma sputtering deposition: ZrxCu1-x metallic glass and AlCoCrCuFeNi high entropy alloy thin films deposited onto silicon. Effects of depositing atom kinetic energies and atomic composition are studied in order to predict evolution of morphologies and atomic structure of MD grown thin films. Experimental and simulated X-ray diffraction patterns are compared.

A radiation source developed for broad band optical absorption spectroscopy measurements

In order to investigate the post-arc period and the hot gas regions surrounding the electrical arc in circuit breakers, a broad band radiation source has been developed to perform absorption spectroscopy measurements. The source consists of a Z-pinch electrical discharge in which the high temperature and the high density argon plasma obtained at maximum compression produces an extremely intense continuous radiation pulse of about 2 μs duration. The radiation spectrum has been characterized both temporally and spectrally in order to determine the best operating conditions to produce an intense and continuous radiation spectrum. Absorption tests have been performed on the hot gas region of a low voltage rail gap circuit breaker. Absorption of copper atom resonance lines (Cu I 324.75 and Cu I 327.40 nm) is used to determine the copper atom density in the rear of the arc. In addition, absorption of the C2 molecule Swan bands, (0,0) and (1,1), is used to determine roughly the concentration of C2 and also the kinetic temperature of the hot gas.

A new optical technique for investigations of low-Voltage circuit breakers

The technique of broad-band optical absorption spectroscopy has been successfully used for investigations of transient media in low-voltage circuit breakers, thanks to an intense radiation source developed at our laboratory. It enabled the determination of the concentration of copper atoms and C/sub 2/ molecules in hot gas behind a moving arc. The temperature of this gas was estimated using the molecular absorption spectrum of C/sub 2/ Swan bands. Thanks to the high-spectral intensity of the auxiliary source, measurements were also performed in an electrical arc. The measurements allowed the determination of the population of excited levels for several metallic atoms in the arc. Assuming local thermodynamic equilibrium, the electron temperature of the arc and the total concentration of these metallic atoms, coming from contacts and splitters, were deduced. This temperature is in good agreement with the one deduced from optical emission spectroscopy.

Experimental study of an electrical discharge used in reactive media ignition

In order to understand the influence of electrical discharges on combustion ignition processes, a wire-to-wire spark created in an air/methane mixture has been studied. The electron temperature and density of this spark discharge have been determined.Voltage, current measurements, photography and optical emission spectroscopy have been used to characterize this discharge as a function of time, pressure and equivalence ratio. The size and shape of the phenomenon were observed using photography. Voltage and current measurement were correlated to these photos to determine the time scale of the discharge and the propagating flame.The Boltzmann plot method was applied to the results of time-resolved spectroscopy during the discharge phase and yielded to the electron temperature the first 10 µs. Finally, from Stark broadening of Hα, Hβ and copper lines, the electron density of the plasma was deduced for the first 10 µs, with values up to 1018 cm−3. These data will be used as the initial condition in a numerical simulation.

Radiation of long and high power arcs

The operators working on electrical installations of low, medium and high voltages can be accidentally exposed to short-circuit arcs ranging from a few kA to several tens of kA. To protect them from radiation, according to the exposure limits, we need to characterize the radiation emitted by the powerful arc. Therefore, we have developed a general experimental and numerical study in order to estimate the spectral irradiance received at a given distance from the arc. The experimental part was based on a very long arc (up to 2 m) with high ac current (between 4 and 40 kA rms, duration 100 ms) using 3 kinds of metallic contacts (copper, steel and aluminium). We measured the irradiance received 10m from the axis of the arc, and integrated on 4 spectral intervals corresponding to the UV, visible, IRA + B and IRC. The theoretical part consisted of calculating the radiance of isothermal plasmas in mixtures of air and metal vapour, integrated over the same spectral intervals as defined in the experiments. The comparison between the theoretical and experimental results has allowed the defining of three isothermal radiation sources whose combination leads to a spectral irradiation equivalent to the experimental one. Then the calculation allowed the deduction of the spectral description of the irradiance over all the wavelength range, between 200 nm and 20 μm. The final results indicate that the influence of metal is important in the visible and UVA ranges whereas the IR radiation is due to the air plasma and surrounding hot gas and fumes.

Experimental Study of a Gas Jet Generated by an Atmospheric Microcavity Discharge

A study of a one-side-opened microcavity discharge in atmospheric-pressure air is reported. This discharge is powered by a DC high voltage power supply. The discharge regime can be self-pulsed or continuous depending on the magnitude of the discharge current. A gas jet, generated by the discharge in the microcavity, can be used to act on an external airflow passing near the orifice of the microcavity in order to control the airflow. Our experiments clearly show that the gas jet significantly disrupts a smoke column passing near the orifice of the microcavity. The smoke column deviation periodically varies when the electrical discharge is in the pulsed regime, whereas in the continuous regime, it becomes constant. Optical emission spectroscopy measurements were performed, and the gas temperature in the cavity as a function of the mean discharge current was estimated.

A continuous non-linear shadowing model of columnar growth

A dental implant for installation into a mouth is disclosed. The implant includes a one piece implant body to which is attached an abutment portion for anchoring a denture or tooth replacement. The implant body includes a coronal portion having a keyway. The abutment portion includes a key which mates with the keyway to form a non-rotational joint. In one aspect of invention, the abutment portion is cemented into the keyway. In another aspect of the invention, the key is tapped in to the keyway to form a cold weld. There is also shown a method of installing a dental implant which includes press fitting the implant body into a preformed cylindrical bore at the implant site. The abstract is made retrievable without disturbing the bone implant interface.

Compact Z-pinch radiation source dedicated to broadband absorption measurements

In order to acquire a broadband absorption spectrum in a single shot, a compact radiation source was developed by using a Z-pinch type electric discharge. This paper presents the mechanical and electrical construction of the source, as well as its electrical and optical characteristics, including the intense continuum of radiation emitted by the source in the UV and visible spectral range. It also shows that the compactness of the source allows direct coupling with the probed medium, enabling broadband absorption measurement in the spectral range of 200–300 nm without use of an optical fiber which strongly attenuates the light in the short wavelength range. Concretely, thanks to this source, broadband spectral absorption of NO molecules around 210 nm and that of OH molecules around 310 nm were recorded in this direct coupling arrangement. Copper atom spectral absorption around 325 nm of the peripheral cold zones of an intense transient arc was also recorded.