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1
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Spatial Structure of Emission Intensity in Capacitive RF Discharge of He:Ne Mixture at Moderate Pressures

100%
Al-Hawat S., Akel M.
Acta Physica Polonica A
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2010
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vol. 117
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issue 6
911-916
EN
The spatial structure of emission intensity in a capacitive radio frequency discharge at 13.56 Mhz in He:Ne mixture with total pressures of more than hundreds of Pascal was studied using the optical emission spectroscopy technique. The spectral line distributions at the axis of the discharge gap vs. the distance between two plane aluminium electrodes were found for: the line of 585.2 nm (Ne) and 447.15 nm (He) in 5:1 ratio of the mixture at pressure of 800 Pa for different driving powers 10, 20, and 30 W; the line of 585.2 nm in the range of 733-4393 Pa at power of 20 W in 10:1 ratio of the mixture; lines of 632.8 + 633.4 nm (Ne) at ratios of 5:1, 10:1, 15:1, a power of 20 W, under pressure of 1400 Pa; lines of 585.2 nm, 632.8 + 633.4 nm, 640.2 nm, and 703.2 nm (Ne) and 447.15 nm, 706.52 nm (He), at a pressure of 1467 Pa and a power of 20 W in ratio 10:1. Under chosen operational conditions, the measured relative spectral intensities for all studied lines in the middle of the discharge gap show the existence of the α-regime in the RF discharge. The dc-bias voltage vs. the total pressure and the dc-bias voltage-power characteristics were obtained at certain conditions.
2
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Effect of Surface Modification by Ammonia Plasma on Vascular Graft: PET Film and PET Scaffold

51%
Öteyaka M., Chevallıer P., Robıtaılle L., Laroche G.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1
125-127
EN
Nowadays, poly (ethylene terephthalate) (PET) textiles, either knitted or woven, are largely used as substitutes for replacement of medium and large calibre (10-40 mm) arteries. Unfortunately, these substitutes do not perform well when they are used to replace small diameter arteries due to thrombogenicity and compliance mismatch issues. Surface treatments were often used as the first step to solve thrombogenicity issues. For example, low pressure ammonia plasma processes can provide modification of the top ≈ 10 - 50 Å of polymer surface without affecting bulk properties of materials. This work compared ammonia plasma surface modifications of PET film (flat surface) and PET scaffolds (porous surface). Plasma treatments lead to a higher amount of nitrogen as well as amino groups on scaffolds compared to films. N/C maximum was reached for PET film and scaffold after plasma treatments of 5 s and 100 s, respectively. Highest amine concentration on films and scaffolds were obtained at short treatment time, specifically 1 s. In addition, high resolution spectra of C 1s confirmed that amino groups were mainly grafted on aromatic rings. Nodule formation was observed after plasma treatment with atomic force microscopy. Their size and shape increased with longer treatment time.
3
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Spectroscopic Study of CO_2 Plasma in Microwave Source Designed for Hydrogen Production via Hydrocarbons Decomposition

51%
Hrycak B., Jasiński M., Mizeraczyk J.
Acta Physica Polonica A
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2014
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vol. 125
|
issue 6
1326-1329
EN
In this paper, results of spectroscopic study of microwave (2.45 GHz) plasma at atmospheric pressure and high CO_2 flow rate are presented. The plasma was generated by waveguide-supplied nozzleless cylindrical type microwave plasma source. Working gas flow rate and microwave absorbed power varied from 50 up to 150 l/min and from 1 up to 5.5 kW, respectively. The emission spectra in the range of 300-600 nm were recorded. The rotational and vibrational temperatures of C_2 molecules, as well as the rotational temperature of OH radicals were determined by comparing the measured and simulated spectra. The plasma gas temperature inferred from rotational temperature of heavy species ranged from 4000 to 6000 K. It depended on location in plasma, microwave absorbed power and working gas flow rate. The presented microwave plasma source can be used in various gas processing applications.
4
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Breakdown Phenomena in Water Vapor Microdischarges

51%
Radmilović-Radjenović M., Radjenović B., Savić M.
Acta Physica Polonica A
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2010
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vol. 117
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issue 5
752-755
EN
The gas breakdown at the large gap sizes is reasonably well understood. However, the breakdown phenomenon in microgaps is still not sufficiently explored. The high electric fields realized in small gaps combined with the lowering of the potential barrier, seen by the electrons in the cathode as ion approaches lead to ion-enhanced field emission leading to deviations from the standard Paschen law. In this paper, semi-empirical expressions for the breakdown voltage based on the fitting of numerical solutions of the DC breakdown criteria in microdsicharges have been derived. In the standard breakdown criteria the secondary emission coefficient that incorporates the enhancement of the secondary electron emission has been included. The obtained expressions can be used for determination the pressure and the gap dependence of the breakdown field strength in the water vapor, separately.
5
Content available remote

Experimental Investigation of Low Power Microwave Microplasma Source

51%
Czylkowski D., Hrycak B., Jasiński M., Mizeraczyk J.
Acta Physica Polonica A
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2014
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vol. 125
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issue 6
1323-1326
EN
The aim of this paper is to present a novel microwave microplasma source generated in different gases at atmospheric pressure. The design, rule of operation and experimental investigations of the new microwave microplasma source are described. The main advantage of the presented microwave microplasma source is its small size, simplicity, and low cost of construction and operation. The microplasma has a form of a small plasma jet of dimensions of a few mm, depending on the kind of gas, gas flow rate, and absorbed microwave power. Presented in this paper results of experimental investigations were obtained with an atmospheric pressure argon, krypton, nitrogen, and air microplasma, sustained by microwaves of standard frequency of 2.45 GHz. The absorbed microwave power was up to 70 W. The gas flow rate was from 2 to 25 l/min. The miniature size, simplicity of the source and stability of the microplasma allow to conclude that the presented new microwave microplasma source can find practical applications in various fields.
6
Content available remote

Wall Confinement Technique by Magnetic Gradient Inversion. Accelerators Combining Induction Effect and Pulsed Ionization. Applications

45%
Petit J., Geffray J.
Acta Physica Polonica A
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2009
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vol. 115
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issue 6
1162-1163
EN
We published the first description of a disk-shaped MHD aerodyne, combining pulsed ionization and induction systems. Magnetic pressure tends to push away electric discharge, in region of low magnetic field. In the seventies the efficiency of the wall confinement, due to the inversion of the magnetic pressure gradient was demonstrated. It is time now for ambitious MHD projects. We have planned experimental studies of MHD acceleration, combining pulsed ionization, wall confinement and induction system. We intend to study pulsed ionization systems based on wall micro discharges or microwaves action. We present the different features of the project.
7
Content available remote

Wall Confinement Technique by Magnetic Gradient Inversion

45%
Petit J., Dore J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 3
611-613
EN
When a plasma is subjected to a transversal magnetic field and its Hall parameter is non-negligible, it weakens the local electric conductivity value. If an electric discharge is created near a wall and the magnetic field decreases with distance, the electric discharge will follow a path that minimises the streamer's electric resistance, which could expel it far from the wall. One solution to ensure that it remains up against the wall is by inversion of the magnetic field's gradient by arranging that field B be minimal at the wall. In the experiment we are presenting, effected in a low-density gas, in order to obtain a high value for the Hall parameter using simple permanent magnets, we will show the remarkable efficiency of this parietal confinement method and present the main lines of the programme of which this experiment forms part and whose successful realization will be the demonstration of the feasibility of the displacement of disk-shaped MHD aerodynes at supersonic speed without creating either shock waves or turbulence, an approach that we have already set out in numerous publications.
8
Content available remote

Nitriding of 4140 Annealed Low Alloy Steel in RF Plasma

45%
de la Piedad-Beneitez A., Muñoz-Castro A., Valencia-Alvarado R., López-Callejas R., Mercado-Cabrera A., Peña-Eguiluz R., Rodriguez-Mendez B., Barocio S.
Acta Physica Polonica A
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2013
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vol. 123
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issue 5
904-906
EN
The annealed low alloy 4140 steel samples have been nitrided for different treatment periods (1-6 h) in an RF inductive plasma discharge with very low bias voltage ( ≈ 400 V). The resulting nitrided layer has been observed by means of an optical microscope whereas the nitride phases have been characterised by X-ray analysis. The corrosion response, assessed by the potentiodynamic tests in the 3.5% NaCl solution, presents both higher noble potential values and lower corrosion rates when compared with the untreated sample. The Vickers microhardness tests values show an appreciable increment compared to that of the untreated sample. The process is characterized by a high overall efficiency because similar average Vickers tests values were obtained, no matter for how long the treatment was extended. Likewise, the scanning electron micrographs confirmed no appreciable size evolution of the compound layer microstructure at different times of treatment.
9
Content available remote

Ion flux's pressure dependence in an asymmetric capacitively coupled rf discharge in NF3

38%
Mateev E., Zhelyazkov I.
Open Physics
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2004
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vol. 2
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issue 1
1-11
EN
Starting from an analytical macroscopic/phenomenological model yielding the self-bias voltage as a function of the absorbed radio-frequency (rf) power of an asymmetric capacitively coupled discharge in NF3 this paper studies the dependence of the ion flux onto the powered electrode on the gas pressure. An essential feature of the model is the assumption that the ions' drift velocity in the sheath near the powered electrode is proportional to E α, where E=−ΔU (U being the self-bias potential), and α is a coefficient depending on the gas pressure and cross section of elastic ion-neutral collisions. The model also considers the role of γ-electrons, stochastic heating as well as the contribution of the active electron current to the global discharge power balance. Numerically solving the model's basic equations one can extract the magnitude of the ion flux (at three different gas pressures) in a technological etching device (Alcatel GIR 220) by using easily measurable quantities, notably the self-bias voltage and absorbed rf power.
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