On phenomena in ionized gases
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- 2. Influence of pressure on the transition
- 2.2. U(I) characteristics
- Discharge regime Arc regime
- Comparison study of different simulation codes for positive streamers propagating into a region below breakdown
- 2. Methodology and Results
- Direct Synthesis of Nanodiamonds by Ar-H 2 -CH 4 Microwave Discharges
- 3. Results and Conclusions
- Acknowledgements
- The influence of air impurities on the evolution of plasma species in a capillary helium plasma jet
- Tube Exit Tube
- Effect of humidity on Partial Discharge Inception Voltage
- 3. Results and discussion
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1. Introduction
Electrical discharges and electric arcs have been extensively investigated. , However, few studies have investigated the transitions between discharge and arc [1-3]. In many electrical power systems, electrical discharges can occur. These electrical discharges may lead to electric arcs, resulting in failure and/or destruction of the system. The aim of this work was to study the role of pressure on transition mechanism. In this objective, a specific power supply, which allows generating both electrical discharges and electric arcs with controlled current intensity, was designed and implemented [4].
Cylindrical copper or tungsten electrodes were placed in a sealed chamber containing argon gas with pressure ranging from 10 3 to 10
5 Pa. . The electrode gap (denoted d) was in the range 3 – 50 mm. For all experiments, electric discharges were first generated by applying high voltage to the argon gas gap. 2.1. Spontaneous transitions
In figure 1 the evolution of the current intensity (in grey) and of the electrode voltage (in black) are plotted.
4 and d = 25mm. In this example where P = 10 4 Pa and d = 25 mm, successive spontaneous discharge-to-arc and arc-to- discharge transitions were observed for approximately constant value of current intensity. These transitions occur in some 100 ns.
In figure 2, U(I) characteristics are plotted for two different pressure values: 10 4 and 9×10 4 Pa.
4 and 9×10 4 Pa
According to the pressure value, transitions could occur for a precise value of the current intensity or for larger range of current intensity. In this range, discharge and arc may successively exist.
[1] M. Saiepour, J.E. Harry, Int. J. Electronics, 1991, vol.70, n°2, pp. 459-465. [2] W.A. Gambling, H. Edels, British Journal of Applied Physics, vol. 5, 1954, pp. 36-39 [3] S.Watanabe, S.Saito, K.Takahashi, T.Onzawa, J. Phys. D: Appl. Phys. 36, 2003, pp. 2521–2525 [4] R. Landfried, PhD thesis, University Paris- Sud 2010 Discharge regime Arc regime 0 200 400 600
800 1000
0 20 40 60 80 100 120 140
160 180
200 220
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Zone where reversible transitions may exist Arc or dis
c harge v
o lt age (V) Arc or discharge current intensity (mA) P = 10 4 Pa - d = 5 mm - Argon P = 9.10 4 Pa - d = 5 mm - Argon Topic number 305
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Comparison study of different simulation codes for positive streamers propagating into a region below breakdown
B. Bagheri P 1 , J. Teunissen P 2 , U. Ebert P 1,3
, and more participants of the study
P 1 Centrum Wiskunde & Informatica, PO Box 94079, 1090 GB Amsterdam, The Netherlands P
Centre for Mathematical Plasma-Astrophysics, KU Leuven, Celestijnenlaan 200B, 3001, Leuven, Belgium P
Department of Applied Physics, Eindhoven University of Technology, The Netherlands
For streamer simulations a range of computational models have been developed by various groups for various purposes. These models differ in dimensionality (2D, 3D), model type (particle, fluid or hybrid approach and further differentiation), possible inclusion of electrodes or dielectrics, transport and reaction coefficients, initial conditions and numerical implementation. The aim of the present study is to benchmark the results of different computational models for axisymmetric single positive streamers in air at 1 bar and 300 K. We have invited potential participants to join on March 1, and we will present the current state of the study in July in a poster.
Streamers are ionized channels with electric field enhancement at their tips that grow rapidly in different gases and liquids. Study of emergence and propagation of streamer discharges have gained a lot of interest from different research groups due to their vast industrial and medical applications. Furthermore, study of streamer discharges is essential since they are responsible for the initial stages of sparks, lightning, and they appear directly as sprite discharges. Computational models of streamers depend on different factors and parameters, such as: • the type of the model, e.g. fluid, particle or hybrid models, and the further approximations taken like local field approximation etc., • dimensionality (2D, axisymmetric or full 3D), • mobility and reaction coefficients, • initial conditions, • the implementation of photo-ionization, • electrode shapes and boundary conditions, and • numerical resolution and accuracy. We aim to study how simulation results depend on these choices and parameters and approximations involved, and on March 1 (2 days before the deadline of this abstract), we have invited other groups internationally to join the study, after an earlier initiative of Sergey Pancheshnyi in October 2016. We now suggest to compare results for a single axisymmetric positive streamer in air. The results of the comparison study will be presented in a poster.
2. Methodology and Results Single positive streamer with cylindrical symmetry with size R=1.25 cm, and L=1.25 cm in air at 300K temperature and 1 bar pressure is studied. A homogenous electric field of -1.5 MV/m is imposed by applying a potential difference of 18.75 kV between the two planar electrodes. A needle electrode protruding from the planar anode is mimicked by inserting a package of positive ions on the axis at z=1 cm. We hope that a number of groups internationally will participate. In Amsterdam, we will use afivo- streamer [1,2] based on the afivo framework [3]. We present the results of the comparison study in a poster.
through the Dutch STW-project 15052, and J.T. through postdoctoral fellowship 12Q6117N of the Belgian-Flemish FWO.
[1] S. Nijdam, J. Teunissen, E. Takahashi, and U. Ebert, Plasma Sources Sci. Technol. 25 (2016) 044001. [2] J. Teunissen, https://gitlab.com/MD-CWI- NL/afivo-streamer [3] J. Teunissen, U. Ebert, Afivo: a framework for
preprint arxiv.org/abs/1701.04329 submitted to Comp. Phys. Comm., https://gitlab.com/MD-CWI- NL/afivo.
Topic 5
306 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Direct Synthesis of Nanodiamonds by Ar-H 2 -CH 4 Microwave Discharges
A. Dias P 1 P , E. Felizardo 1 , M. V. Abrashev 2 , A. Almeida 3 ,
J. Henriques UP 1 P , E. Tatarova 1 P
P
P
A experimental study on microwave plasma based assembly of nanodiamonds at atmospheric pressure conditions is presented. The synthesis method is based on introducing a carbon containing precursor (methane), through a microwave (2.45 GHz) argon plasma environment, where decomposition of methane molecules takes place and carbon atoms and molecules are created and then converted into solid carbon nuclei in the post-discharge zone. The influence of additional hydrogen gas injected into the background gas mixture on the carbon species production and on the structural qualities of fabricated nanodiamonds has been investigated. Optical emission, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction techniques (XRD) have been applied to study plasma emissions, the output gas stream composition, and the material and chemical analyses of synthesized nanostructures.
Nanodiamonds have a 3D structure formed by sp 3 bounded carbon atoms arranged in a tetrahedral symmetry and their dimensions are in the range 2-5 nm. Nanodiamonds have a distinct combination of outstanding unique
mechanical, chemical, biological, magneto-optical and electronic properties, which can be improved by adding functional groups. Moreover, they are nontoxic and can be used in biomedical applications, as drug carriers and delivery vehicles. Nanodiamonds are not destroyed by the human immune systems, and can be associated with a multitude of molecules and give targeted drug release. Usually extreme environment are necessary to synthesize nanodiamonds. Nanodiamonds can be found with extremely low concentrations on Earth in crude oil and in certain sediment layers, or in space, in meteorites, interstellar dust or in protoplanetary nebulae. The frequently used method is detonation of high explosive materials. 2. Experimental Setup
Nanodiamonds have been produced by a surface wave induced
microwave plasma,
using a waveguide surfatron-based setup. The microwave power is provided by a 2.45 GHz generator (Sairem), with maximum power of 2 kW. The generator is connected to a waveguide (WR-340) system, which includes an isolator, directional couplers, a three-stub tuner, a moveable short-circuit and a waveguide surfatron as the field applicator. The discharge ignites in a quartz tube, placed vertically and perpendicularly to the waveguide wider wall. A methane (CH 4 ) and hydrogen (H 2 ) gas
mixture is introduced into the "hot" microwave argon plasma environment, where decomposition of methane molecules takes place and carbon atoms and molecules are created. Afterwards, carbon atoms and molecules are converted into solid carbon nuclei in the "colder" nucleation zones where nanometer-size particles are generated. The addition of H
2 is important since the surface of sp 3 clusters must be either stabilized through termination with functional groups or reconstructed into sp 2 carbon. 3. Results and Conclusions
XRD, Raman and SEM results showed that atomic hydrogen can kinetically etch the non- diamond sp 2 -C and allow diamond-phase sp 3 -C to
grow. The stability of the nanodiamonds may also depend on the surface terminations, i.e. hydrogen bonds on the nanodiamonds boundaries, therefore, this method can be tuned from non-diamond to diamond phase growth, by controlling the C:H ratio in the gas mixture.
This work was funded by Portuguese FCT— Fundação para a Ciência e a Tecnologia, under Project
UID/FIS/50010/2013, Project
INCENTIVO/FIS/LA0010/2014, and
grant SFRH/BD/52413/2013 (PD-F APPLAuSE)
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XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
The influence of air impurities on the evolution of plasma species in a capillary helium plasma jet
C. Lazarou 1 , C. Anastassiou 1 , F. D. Klute 2 , J. Franzke 2 , G. E. Georghiou 1
1 FOSS Research Centre for Sustainable Energy, Department of Electrical and Computer Engineering, University of Cyprus, Nicosia, 1678, Cyprus 2 ISAS—Leibniz Institut für Analytische Wissenschaften, Bunsen-Kirchhoff-Str. 11, 44139 Dortmund, Germany
The main aim of this paper is to numerically investigate the evolution of the different species in a capillary helium plasma jet, during the plasma bullet propagation. This study is performed for a wide range of air concentrations in the helium jet core (up to 16000 ppm). The simulation results showed that the helium species are only produced and propagated in the helium jet core (along the axis of symmetry of the tube). On the other hand, the nitrogen and oxygen species (for up to 7000 ppm air in the jet core) were produced and propagated at the side of the jet core. For air concentration levels (in the jet core) higher than 7000 ppm, the production and propagation of the nitrogen and oxygen species converges towards the helium jet core. In order to interpret the results, the mean reaction pathways behind the production of each species are examined. This analysis provides useful insight into the physics behind the evolution and characteristics of the plasma jet.
In recent years, the atmospheric pressure plasma jet (APPJ) has gained much attention due to its low production costs and the wide range of applications. Although significant progress in the understanding of the basic principles of the APPJ has been made, certain areas, such as the evolution and creation of the plasma species, need further research. With this in mind, a two dimensional axisymmetric model was developed [1], for the study of the helium plasma jet. The configuration and the operational parameters of the helium plasma jet used in the simulation model are the same as for the experimental setup [2]. In Figure 1, the spatial profile of the level of air concentration used as input in the plasma fluid model is shown.
The simulation results showed that the plasma bullet propagated along the axis of symmetry of the tube. The high energetic electrons that promote the reactions pathways for the
plasma bullet
propagation, has its peak on the plasma bullet head and a crescent like shape centred on the axis of symmetry of the tube. The helium species concentration peaks along the axis of symmetry where the helium ground state atoms are at their maximum. For levels of air below 7000 ppm in the jet core (~ 0.22 cm from the tube exit) the nitrogen and oxygen ground state molecule
concentrations are higher towards the edges of the helium jet whilst their species are generated towards the centre due to the higher electron energy there. As the distance from the tube exit increases, so does the air concentration in the jet core. Once it increases beyond 7000 ppm, the reaction pathways for the
production of the nitrogen and oxygen species move towards the axis of symmetry. These results provide good insight into the physics behind the plasma jet evolution and the experimentally observed emitted light.
Figure 1: Plasma jet and the distribution of air concentration (ppm) in the domain . References [1] C. Lazarou, T. Belmonte, A. S. Chiper and G. E. Georghiou 2016 Plasma Sources Sci. Technol. 25 055023
[2] V. Horvatic, A. Michels, N. Ahlmann, G. Jestel, C. Vadla and J. Franzke 2015 Spectrochim. Acta Part B At. Spectrosc. 113 152–7 Topic number: 10 Tube Exit
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XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Effect of humidity on Partial Discharge Inception Voltage
L. Benmamas, R. Boukadoum, R. Landfried, T. Leblanc, E. Odic, P. Teste
The aim of this paper was to investigate the impact of humidity on the Partial Discharge Inception Voltage (PDIV). The effect of humidity was quantified by measuring the PDIV for metallic parallel electrodes under DC voltage and atmospheric pressure. The study was made in absolute humidity in the range [2-80g/m 3 ], for two temperatures T=25°C and T=50°C. To control environmental conditions a climatic chamber allowing Pressure, Temperature and humidity (P, T, H) variations is used. Considering that the humidity is slightly depending on temperature, the main result of this study shows different PDIV behaviours as a function of humidity for the two considered temperatures.
The work presented in here is part of a larger study concerning the analysis of breakdown voltage under aeronautical environmental conditions. Many works were interested by the influence of the humidity on PDIV values on enamelled wires [1], [2]. Here we propose to investigate the case of non- insulated electrodes.
Figure 1 shows the experimental set-up used to perform PDIV measurements. The studied device was two metallic spherical electrodes without any solid insulation. The environmental parameters were controlled using a climatic chamber.
Figure 1: experimental set-up 3. Results and discussion Figure 2 shows that at T=25°C, the PDIV decreases as the absolute humidity increase until HA=10g/m3, and slightly increases above HA=10g/m3. At higher temperature T=50°C, the behaviour is slightly different: first, PDIV increases with humidity before slightly decreasing above HA=45g/m 3 . In the interval [10g/m 3 - 45g/m 3 ] the PDIV increases because of water evaporation acting like an electro- negative gas, attaching the electrons responsible of discharges so increasing PDIV. Above this range, the electric field is enhanced locally around water particles created by condensation, so decreasing the PDIV. These observations are in accordance with [1], [2]. These results highlight the importance of correlation between temperature and humidity.
Figure 2: PDIV as a function of absolute humidity for different distances at T=25°C and T=50°C References [1] Y. Kikuchi, T. Murata, Y. Uozumi, N. Fukumoto, M. Nagata, Y. Wakimoto, and T. Yoshimitsu, “Effects of ambient humidity and temperature on partial discharge characteristics of conventional and nanocomposite enameled magnet wires,” IEEE Trans. Dielectr. Electr. Insul., vol. 15, no. 6, pp. 1617–1625, 2008. [2] M. Fenger and +G. C. Stone, “Investigations into the Effect of Humiditv on Stator Winding Partial Discharges,” vol. 12, no. April, pp. 341–346, 2005.
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