Denis Packan

Nonequilibrium discharges in air and nitrogen plasmas at atmospheric pressure

Diffuse glow discharges were produced in low temperature (<2000 K) atmospheric pressure air and nitrogen plasmas with electron number densities in excess of 1012 cm3, more than six orders of magnitude higher than in thermally heated air at 2000 K. The measured discharge characteristics compare well with the predictions of a two-temperature kinetic model. Experimental and modeling results show that the steady-state electron number density exhibits an S-shaped dependence on the electron temperature, a behavior resulting from competition between ionization and charge-transfer reactions. Non-Maxwellian effects are shown to be unimportant for the prediction of steady-state electron number densities. The power requirements of DC discharges at atmospheric pressure can be reduced by several orders of magnitude using short repetitive high-voltage pulses. Between consecutive pulses, the plasma is sustained by the finite rate of electron recombination. Repetitive discharges with a 100-kHz, 12-kV, 10-ns pulse generator were demonstrated to produce over 1012 electrons/cm3 with an average power of 12 W/cm3, 250 times smaller than a DC discharge at 1012 cm3.

Direct-current glow discharges in atmospheric pressure air plasmas

Investigations have been conducted to experimentally validate the mechanisms of ionization in two-temperature atmospheric pressure air plasmas in which the electron temperature is elevated with respect to the gas temperature. To test a predicted S-shaped dependence of steady-state electron number density on the electron temperature and its macroscopic interpretation in terms of current density versus electric field, direct-current (dc) glow discharge experiments have been conducted in flowing low temperature, atmospheric pressure air plasmas. These experiments show that it is feasible to create stable diffuse glow discharges with electron number densities in excess of 1012 cm−3 in atmospheric pressure air plasmas. Electrical characteristics were measured and the thermodynamic parameters of the discharge were obtained by spectroscopic measurements. The measured gas temperature is not noticeably affected by whether or not the dc discharge is applied. The discharge area was determined from spatially resolved...

DC and pulsed glow discharges in atmospheric pressure air and nitrogen

This article illustrates a variety of direct current and pulsed glow discharges obtained either in ambient or preheated (2000 K) air or nitrogen at atmospheric pressure. The images presented show that stable and diffuse discharges, with electron densities as high as 10/sup 12/ cm/sup -3/, can be obtained at atmospheric pressure with no filamentation or constriction. Spectroscopic measurements confirm that these discharges are of the glow type.

Optimization of a coaxial electron cyclotron resonance plasma thruster with an analytical model

A new cathodeless plasma thruster currently under development at Onera is presented and characterized experimentally and analytically. The coaxial thruster consists of a microwave antenna immersed in a magnetic field, which allows electron heating via cyclotron resonance. The magnetic field diverges at the thruster exit and forms a nozzle that accelerates the quasi-neutral plasma to generate a thrust. Different thruster configurations are tested, and in particular, the influence of the source diameter on the thruster performance is investigated. At microwave powers of about 30 W and a xenon flow rate of 0.1 mg/s (1 SCCM), a mass utilization of 60% and a thrust of 1 mN are estimated based on angular electrostatic probe measurements performed downstream of the thruster in the exhaust plume. Results are found to be in fair agreement with a recent analytical helicon thruster model that has been adapted for the coaxial geometry used here.

Measurement and Modeling of OH, NO, and CO Infrared Radiation at 3400 K

The infrared emission spectrum of an air plasma containing small quantities of CO 2 and H 2 O was measured and modeled in absolute intensity in the spectral range 2.4-5.6 μm. A 50-kW radio-frequency inductively coupled plasma torch was used to produce the air plasma in local thermodynamic equilibrium. The temperature profile measured by emission spectroscopy peaks at 3400 K. The absolute intensity emission spectrum was measured and compared with numerical simulations obtained with the line-by-line radiation code SPECAIR. Spectroscopic models incorporated into the SPECAIR code include the infrared rovibrational bands of OH, NO, and CO. Absorption of the plasma emission by room-air CO 2 and H 2 O in the optical path between the plasma and the detector is taken into account. Plasma emission from CO 2 (v 1 + v 3 ) and (v 3 ) bands is also modeled, using a correlated-k model

E. coli electroeradication on a closed loop circuit by using milli-, micro- and nanosecond pulsed electric fields: comparison between energy costs.

One of the different ways to eradicate microorganisms, and particularly bacteria that might have an impact on health consists in the delivery of pulsed electric fields (PEFs). The technologies of millisecond (ms) or microsecond (μs) PEF are still well known and used for instance in the process of fruit juice sterilization. However, this concept is costly in terms of delivered energy which might be too expensive for some other industrial processes. Nanosecond pulsed electric fields (nsPEFs) might be an alternative at least for lower energetic cost. However, only few insights were available and stipulate a gain in cost and in efficiency as well. Using Escherichia coli, the impact of frequency and low rate on eradication and energy consumption by msPEF, μsPEF and nsPEF have been studied and compared. While a 1 log10 was reached with an energy cost of 100 and 158 kJ/L with micro- and millisecond PEFs respectively, nsPEF reached the reduction for similar energy consumption. The best condition was obtained for a 1 log10 deactivation in 0.5h, for energy consumption of 143 kJ/L corresponding to 0.04 W · h when the field was around 100 kV/cm. Improvement can also be expected by producing a generator capable to increase the electric field.

Characterization of a coaxial ECR plasma thruster

The Electron Cyclotron Resonance (ECR) plasma thruster is an electric propulsion device that combines the high ionization performances of an ECR source and the simultaneous acceleration of electrons and ions in a magnetic nozzle. A coaxial ECR thruster under development at ONERA is tested using xenon as the propellant gas. The influence of mass flow rate and microwave power on ion current and ion energy distribution is evaluated. Mass utilization efficency up to 45% and ion energy up to 350 eV have been obtained with a microwave power around 50 W.

Repetitively-pulsed DC glow discharge in atmospheric pressure air: modeling and experiments with a 12 kV, 10 Ns, 100 kHz pulse generator

Summary form only given, as follows. Low-temperature, low-power atmospheric-pressure air plasmas with high electron number densities have numerous potential applications such as medical sterilization, biochemical decontamination and EM-wave shielding. DC discharges can be used to create such plasmas, but as most of the energy goes into vibrational excitation of nitrogen molecules the power budget is extremely large (about 30 kW/cm/sup 3/ for n/sub e/=10/sup 13/ cm/sup -3/). The power budget can be greatly reduced however through the use of high-voltage electric pulses. In an air discharge under a wide range of conditions, the rate of recombination of electrons is approximately set by n/sub e/ and must be compensated for by ionization. DC discharges can maintain n/sub e//spl sim/10/sup 13/ cm/sup -3/ with electric fields producing electron temperatures on the order of 1 eV. Short (1-10 ns)-pulse discharges require higher peak electron temperatures of about 3-5 eV. As the energy lost to nitrogen molecules, per electron created, is several orders of magnitude smaller at T/sub e/=3 eV than at T/sub e/=1 eV, the ionization efficiency is much larger in the pulsed case than in the DC case, and the power budget decreases accordingly. We have devised a repetitively-pulsed discharge scheme using this principle. Parametric studies of the pulsed-discharge parameters were performed with a 2-temperature chemical-kinetic and a collisional-radiative model. A power reduction of more than 2 orders of magnitude at n/sub e/=10/sup 13/ cm/sup -3/ is predicted. This result is supported by experiments conducted in our laboratory with a single electric pulse. Experiments using a 100 kHz repetitive pulse generator, with typical voltage pulses of 12 kV amplitude and 10 ns FWHM, have also been conducted in atmospheric-pressure air at 1800 K. Electrical and optical measurements of the discharge are compared to the modeling predictions. The experimental and modeling results to date indicate that low-temperature atmospheric pressure air plasmas with n/sub e//spl sim/3/spl times/10/sup 12/ cm/sup -3/ can be sustained with power requirements of /spl sim/60 W/cm/sup 3/.

SCALED-UP NONEQUILIBRIUM AIR PLASMAS

The volume scalability of nonequilibrium plasmas produced by electrical discharges in atmospheric pres- sure air has been investigated. A variety of direct current (DC) and pulsed glow discharges obtained in either slow flow of ambient or fast flow of preheated (~2000 K) air at atmospheric pressure is presented. Single DC and repeti- tively pulsed discharges represent the first approach. Stable discharges with electron number densities as high as 10 12 cm -3 were obtained without filamentation. A large decrease of the input power by 2-3 orders of magnitude was achieved in pulsed discharges, in comparison with the DC discharges. A dual-discharge facility was developed that combines two parallel DC discharges in either ambient or preheated air. Uniform plasma volumes of a few cubic centimeters have been achieved by this technique. Multiple pulsed discharges in parallel have been examined as well in order to increase the plasma volume. Finally, some paradoxical results on DC discharges in transverse gas flow are presented. The temperature distribution effecting the reduced electric field E/N is found to strongly influ- ence the shape of the discharge.

Direct-current glow discharges in atmospheric pressure air and nitrogen plasmas

Summary form only given. There is considerable interest in methods for efficiently producing large volumes of atmospheric pressure air plasmas at gas temperatures below 2000 K with free electron densities of 10/sup 13/ cm/sup -3/. One approach consists in targeting the energy addition to the free electrons by application of electric fields. Investigations have been conducted to understand and validate the mechanisms of ionization in two-temperature atmospheric pressure air and nitrogen plasmas in which the electron temperature is elevated with respect to the gas temperature. With a new two-temperature chemical kinetic model for air and nitrogen plasmas, we found that, for a given gas temperature, the steady state electron number density exhibits an S-shaped dependence on the electron temperature. This S-shaped behavior is the result of competition between ionization and charge transfer reactions and is characteristic of molecular plasmas. The numerical results are then interpreted in terms of macroscopic discharge parameter (electric field and current density) by means of Ohms law and the electron energy equation. The resulting current density vs. electric field characteristic also exhibits an S-shaped dependence. DC glow discharge experiments have been conducted in flowing low temperature atmospheric air and nitrogen plasmas. Electrical characteristics were measured and the thermodynamic parameters of the discharge were obtained by spectroscopic measurements.