949 research outputs found
Influence of a plasma jet on the hydrodynamics of a helium jet
In this paper, we present a study of the influence of non-equilibrium microplasma jets (“plasma bullets”) on the hydrodynamics of a helium jet operating in open air. The helium jet is produced by a flow of helium through a hollow, cylindrical microdischarge configuration. A plasma jet, triggered by the microdischarge, can propogate in the laminar zone of the helium jet which extends some distance from the exit plane of the microdischarge. We used Schlieren photography to visualize the point of transition from laminar to turbulent regime of the helium jet and the change in the transition point due to the plasma jet for different operating conditions
Xenon excimer emission from pulsed high-pressure capillary microdischarges
Intense xenon vacuum ultraviolet (VUV) emission is observed from a high-pressure capillary cathode microdischarge in direct current operation, by superimposing a high-voltage pulse of 50 ns duration. Under stagnant gas conditions, the total VUV light intensity increases linearly with pressure from 400 to 1013 mbar for a fixed voltage pulse. At fixed pressure, however, the VUV light intensity increases superlinearly with voltage pulse height ranging from 0.8 to 2.8 kV. Gains in emission intensity are obtained by inducing gas flow through the capillary cathode, presumably because of excimer dimer survival due to gas cooling
Oscillation modes of dc microdischarges with parallel-plate geometry
Two different oscillation modes in microdischarge with parallel-plate
geometry has been observed: relaxation oscillations with frequency range
between 1.23 and 2.1 kHz and free-running oscillations with 7 kHz frequency.
The oscillation modes are induced by increasing power supply voltage or
discharge current. For a given power supply voltage, there is a spontaneous
transition from one to other oscillation mode and vice versa. Before the
transition from relaxation to free-running oscillations, the spontaneous
increase of oscillation frequency of relaxation oscillations form 1.3 kHz to
2.1 kHz is measured. Fourier Transform Spectra of relaxation oscillations
reveal chaotic behaviour of microdischarge. Volt-Ampere characteristics
associated with relaxation oscillations describes periodical transition between
low current, diffuse discharge and normal glow. However, free-running
oscillations appear in subnormal glow only.Comment: Submitted to: New Journal of Physic
The influence of power and frequency on the filamentary behavior of a flowing DBD-application to the splitting of CO2
In this experimental study, a flowing dielectric barrier discharge operating
at atmospheric pressure is used for the splitting of CO2 into O2 and CO. The
influence of the applied frequency and plasma power on the microdischarge
properties is investigated to understand their role on the CO2 conversion.
Electrical measurements are carried out to explain the conversion trends and to
characterize the microdischarges through their number, their lifetime, their
intensity and the induced electrical charge. Their influence on the gas and
electrode temperatures is also evidenced through optical emission spectroscopy
and infrared imaging. It is shown that, in our configuration, the conversion
depends mostly on the charge delivered in the plasma and not on the effective
plasma voltage when the applied power is modified. Similarly, at constant total
current, a better conversion is observed at low frequencies, where a less
filamentary discharge regime with a higher effective plasma voltage than that
at a higher frequency is obtained
Argon excimer emission from high-pressure microdischarges in metal capillaries
We report on argon excimer emission from high-pressure microdischarges formed inside metal capillaries with or without gas flow. Excimer emission intensity from a single tube increases linearly with gas pressure between 400 and 1000 Torr. Higher discharge current also results in initial intensity gains until gas heating causes saturation or intensity drop. Argon flow through the discharge intensifies emission perhaps by gas cooling. Emission intensity was found to be additive in prealigned dual microdischarges, suggesting that an array of microdischarges could produce a high-intensity excimer source
On-a-chip microdischarge thruster arrays inspired by photonic device technology for plasma television
This study shows that the practical scaling of a hollow cathode thruster device to MEMS level should be possible albeit with significant divergence from traditional design. The main divergence is the need to operate at discharge pressures between 1-3bar to maintain emitter diameter pressure products of similar values to conventional hollow cathode devices. Without operating at these pressures emitter cavity dimensions become prohibitively large for maintenance of the hollow cathode effect and without which discharge voltage would be in the hundreds of volts as with conventional microdischarge devices. In addition this requires sufficiently constrictive orifice diameters in the 10µm – 50µm range for single cathodes or <5µm larger arrays. Operation at this pressure results in very small Debye lengths (4 -5.2pm) and leads to large reductions in effective work function (0.3 – 0.43eV) via the Schottky effect. Consequently, simple work function lowering compounds such as lanthanum hexaboride (LaB6) can be used to reduce operating temperature without the significant manufacturing complexity of producing porous impregnated thermionic emitters as with macro scale hollow cathodes, while still operating <1200°C at the emitter surface. The literature shows that LaB6 can be deposited using a variety of standard microfabrication techniques
Improvement of adhesive toughness measurement
The double cantilever beam (DCB) method for adhesive toughness measurement was improved by incorporating a sufficiently sharp crack made by a wedge-tapping method. A known route to producing cracks via loading–unloading cycles was proved unreliable because the cycles produced plastic deformation in the adhesive where new cracks propagated. Abnormally high toughness values with large standard deviations were obtained with cracks made by embedding a non-sticky insert. Only instantly propagated cracks made by tapping were sufficiently sharp to produce reproducible, accurate tough-ness measurements. However, toughened resin was insensit
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