On phenomena in ionized gases
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- 2. Experiment and simulations
- References
- Parameters of tap water treated by cold plasma discharges over the surface and inside water
- Understanding the electron and vibration kinetics in CO 2 plasmas
- 1. General and model description
- Surface Functionalization of Fluoropolymers with Amino and Carboxyl Groups by Atmospheric Pressure Plasma Jets with Substrate Biasing
- 2. Experimental setup and results
- Discharge properties in gas filled micro voids in XLPE material
- 2. Brief model description
- Effect of space charge on electron emission in vacuum
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1. Introduction Atmospheric pressure plasma sources have been researched extensively for a wide variety of applications ranging from
biomedicine to
sustainable chemical feedstock production. For any application of these plasma sources to achieve its full potential control of both charged and neutral species dynamics is of key importance. However, only limited control is possible in plasma sources operated with a single fixed frequency. In low- pressure plasma sources, enhanced control has been demonstrated by employing multiple driving frequencies. In this work, we investigate multiple frequency operation for control of radio-frequency (rf) driven atmospheric pressure plasma sources using experimental measurements and numerical simulations.
The plasma source used in this study has the same critical dimensions as the “COST Reference Microplasma Jet” [1]. The source is driven by tailored voltage waveforms (TVW) consisting of a fundamental frequency of 13.56 MHz with up to five harmonics. Both “pulse-type” and “sawtooth- type” waveforms are investigated. The plasma is formed in a feed gas of He with small N 2 admixtures. In order to observe the time and space resolved electron dynamics in the plasma we apply Phase Resolved Optical Emission Spectroscopy (PROES).
The experimental measurements are complemented by 1D fluid simulations using the model discussed in detail in [2, 3]. 3. Results Experimentally, it is observed that the time and space resolved electron dynamics are strongly dependent on the number of harmonics constituting the driving
voltage waveform. Significant differences are also observed in the electron dynamics in plasmas driven by “pulse-type” and “sawtooth-type” waveforms. Simulations carried out under the same operating conditions demonstrate that this control of the time and space resolved electron dynamics results in control over the time and space averaged electron energy distribution function (EEDF). The simulations further show that this allows for control over the densities of both charged and neutral species in the plasma.
The wide range of control possible using this technique offers significant potential to tailor plasma properties in different gas mixtures for specific applications, which will be of importance for future applications of atmospheric pressure plasmas in industry and biomedicine.
This work has been done within the LABEX Plas@Par project, and received financial state aid managed by the ‘Agence Nationale de la Recherche’, as
part of
the ‘Programme d’Investissements d’Avenir’ under the reference ANR-11-IDEX- 0004-02. Funding through UK EPSRC (EP/ K018388/1) and the York-Paris Low Temperature Plasma Collaborative Research Centre is also acknowledged. [1] J. Golda et al. J. Phys. D: Appl. Phys. 49 (2016) 084003.
[2] C. O'Neill, et al, Appl. Phys. Lett., 101 (2012) 154107 [3] J. Waskoenig, J. and T. Gans, Appl. Phys. Lett., 96 (2010) 181501
Topic number 10 296 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Parameters of tap water treated by cold plasma discharges over the surface and inside water
M. El Shaer P , M. Mobasher P , M. Habib, M. Samir PEARLZ (Plasma & Energy Applications Research Laboratory, Zagazig), Faculty of Engineering, Zagazig University, Zagazig, Egypt
Cold plasma applications in many fields, as plasma medicine and plasma agriculture, involve discharges in air above water surface or directly inside water. We have measured parameters of tap water as pH value, ORP, conductivity and nitrate concentration for two types of discharges: pin- water surface DBD above water and pin to plate corona discharge inside water. In the first case, pH is nearly constant on the beginning of discharge time and decreases for longer time giving acidic water, while conductivity, ORP and nitrate concentration increase. For discharge inside water, pH remains constant, as well as conductivity, ORP and nitrate remains at normal level. From these results, we see that acidic medium needed for sterilization is better obtained by discharges in air outside water while for drinking water and agriculture, discharges inside water are more suitable.
In plasma medicine and plasma agriculture different discharge schemes are applied outside or inside water [1]. This influences the physical and chemical properties of treated water. Two types of discharges are considered, pin-water surface dielectric barrier discharge (DBD) above water surface and pin to plate corona discharge inside water. During plasma treatment, tap water parameters as pH, ORP, conductivity and nitrate concentration are measured.
Pin-water surface DBD occurs between a needle above water surface and a counter electrode placed outside the glass container bottom, as shown in Fig. 1-a. An AC signal of 5.7 kHz and 2 KV is used. Needle to plate corona in water is made by discharging a single tri-plate Blumlein capacitor of 2 nF charged by DC high voltage, as shown in Fig.1-b. Water parameters as pH value and conductivity are measured using HI98129 meter, ORP by HI98120 meter and nitrate by test kit HI3874.
-a-
-b-
Fig. 1, a- pin-water surface DBD, b- pin to plate Corona
pH, conductivity, ORP and nitrate concentration for tap water under pin-water surface DBD outside water and pin to plate corona inside water are shown in Fig 2 -a and 2-b.
-a-
-b-
Fig. 2, water parameters for discharges outside water (a) and inside water (b)
Depending on applications requiring certain tap water parameters, we choose between discharge initiated in air outside water surface or inside water.
[1] P. Bruggeman, C. Leys, J. Phys. D: Appl. Phys. 42 (2009) 053001. Topic number: 17 297
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Understanding the electron and vibration kinetics in CO 2 plasmas
T. Silva 1 , M. Grofulović 1 , B. L. M. Klarenaar 2 , O. Guaitella 3 , R. Engeln 2 , C. D. Pintassilgo 1,4
1
P 1 P
2 Department of Applied Physics, Eindhoven University of Technology, The Netherlands 3 LPP, Ecole Polytechnique, UPMC, Université Paris Sud-11, CNRS, Palaiseau, France 4 Departamento de Engenharia Física, Faculdade de Engenharia, Universidade do Porto, Portugal
This work contributes towards a detailed CO 2 kinetic scheme that describes the input and relaxation of vibrational energy in CO 2 plasmas. The vibrational energy exchanges in CO 2
discharges and post-discharges are investigated through a self-consistent model describing the time evolution of the population of individual vibrational levels of the CO 2 (X 1 + ) molecule.
The different processes taken into account include the electron-vibration (e-V), vibration-vibration (V- V) and vibration-translation (V-T) energy exchanges. The model was validated by comparing the calculated densities of vibrationally-excited CO 2 molecules with experimental data obtained in a pulsed CO 2 glow discharge. 1. General and model description The growing interest to plasma-based greenhouse gas decomposition requires the knowledge of the different kinetic mechanisms inherent in CO 2 discharges and post-discharges. To this purpose, we developed a kinetic scheme to describe the time- resolved densities of several CO 2 vibrational levels. More specifically, the rate balance equations for the creation and loss of the levels are investigated. The different processes taken into account include electron-vibration (e-V), vibration-vibration (V-V) and vibration-translation (V-T) energy exchanges. As a starting point, we have assumed a low excitation regime in which only a few CO 2
vibrational levels are excited, such as in pulsed discharges at low specific energy input and short pulse durations [1].
To validate our model, the calculated concentrations of the CO 2 vibrational levels were compared with the experimental densities (obtained via time-resolved in situ Fourier Transform Infrared spectroscopy) in a low-pressure pulsed CO 2 DC glow discharge. The system under analysis operates with pressure p = 5 Torr, current I = 50 mA and a pulse width of 5 ms. More details about the experimental setup are given in [1]. As illustration of this analysis, Fig. 1 shows the calculated and measured results of the relative densities of the first vibrationally-excited CO 2 levels associated to the bending vibrational mode ?????? 2 during the afterglow of the pulsed discharge. As one can see, there is a very good agreement between the calculated and experimentally determined densities, which is also
extended to the population of the vibrational levels in the other modes and to the active discharge phase (not shown here).
Fig. 1: Normalized density of the first CO 2 bending states during the afterglow of a pulsed DC discharge. Open symbols represent the calculations, while closed symbols the experimental data. N
and g represent the ground state density and statistical weight, respectively.
This work was partially supported by the Portuguese FCT, Projects UID/FIS/50010/2013 and PTDC/FIS-PLA/1420/2014 (PREMiERE). VG and RE have been supported by LABEX Plas@par receiving financial support managed by the Agence Nationale de la Recherche under the reference ANR-11-IDEX-0004-02.
[1] B.L.M. Klarenaar, R. Engeln, M.A. Damen, et al., contribution submitted to ICPIG, (2017). Topic number 5 298
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Surface Functionalization of Fluoropolymers with Amino and Carboxyl Groups by Atmospheric Pressure Plasma Jets with Substrate Biasing
M. Nagatsu 1,2 , and M. Kimpara 2
P 1 P
P
P
Fluoropolymers are difficult materials to modify their surfaces because of the presence of strong C-F and C-C bonds. Surface modifications by low pressure plasma surface treatment have proven to be efficient, but it needs costly high-vacuum systems. In this study, the surface modification of fluoropolymer films with amino- and carboxyl-groups was performed by using atmospheric pressure plasma jet under negatively-biased substrate condition. Ion bombardment effect onto the polymer surface due to negative substrate bias will make dangling bonds and eventually improve the chemical modification on the surface. Functionalized surfaces were analyzed by XPS to confirm the breaking C-F bond and creating C-C or C=O bond. Fluorescence patterns where the fluorescent dyes connect specifically with the amino or carboxyl group, respectively, were clearly observed by fluorescence microscope.
1. Introduction Fluoropolymers, such as polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer (PFA), fluorinated ethylene-propylene(FEP), etc.,
have been widely used in various industrial fields, because of their excellent chemical, mechanical and electrical properties. In this study, amino- and carboxyl-group modification of fluoropolymer sheets was performed by using an atmospheric pressure plasma jet(APPJ) under a negatively-biased substrate condition. 1,2
the polymer surface will serve to modify the surface with functional groups more efficiently. 2. Experimental setup and results In this experiment, PTFE films with a thickness of 50 µm or 1 mm were used. The PTFE film was fixed on the stage by a carbon tape and was masked by a Cu grid, as illustrated in Fig. 1(a). The APPJ plasma was generated by applying a high voltage of ±8 kV with a frequency of 5 kHz and duty ratio of 50% to the electrodes. Fluoropolymer films were modified by two types of functional groups by changing gas species. While He/NH 3 gas mixture was used for amino group modification, He/O 2 gas mixture was used for carboxyl group modification.
Figs. 1(b) and (c) show fluorescent microscope images of PTFE surface after amino- and carboxyl-group modification, respectively. Fluorescence pattern shows clear modification in the maskless area. Figure 2 shows the XPS spectra of C 1s and N 1s of amino group modified PTFE surface. It is clearly seen that the CF 2 peak intensity dropped to generate C-C or C=O bonds after plasma treatment, and NH
2 at ~400 eV peak was appeared. The details of other experimental results will be presented at the conference.
Fig. 1 (a) Experimental setup of APPJ, and fluorescence images of (b) amino group and (c) carboxyl group modification, respectively.
Fig. 2 XPS spectra of C 1s and N 1s for untreated and H/NH 3
References [1]
T. Abuzairi, M. Okada, Y. Mochizuki, N.R. Poespawati, R.W. Purnamaningsih, M. Nagatsu: Carbon 89 (2015) 208-216. [2]
Appl. Surf. Sci. 390 (2016) 489-496. Topic number 14 Cu mask Fluorocarbon film Atmospheric pressure plasma jet Bias voltage
Substrate stage (a)
(b) (c)
410 408
406 404
402 400
398 396
394 410
408 406
404 402
400 398
396 394
300 298
296 294
292 290
288 286
284 282
280 300
298 296
294 292
290 288
286 284
282 280
C 1s N 1s
CF 2 292eV CF 2 NH 2 ~400eV
Binding energy (eV) Binding energy (eV) C-C 284.5eV
untreated untreated He/NH 3
He/NH 3 plasma 299 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Discharge properties in gas filled micro voids in XLPE material
S. Gortschakow P , M. Bogaczyk P , R. Kozakov P
P
Micro voids belong to typical defects in medium voltage cross-linked polyethylene (XLPE) cables. Application of high voltage can causes micro discharges in the medium, which fills the void. Besides the liquid products, methane and ethylene are the major components in a void. Properties of the micro discharges in a dielectric encapsulated void of typical size 3-10 µm have been studied by time- and space-dependent numerical model in a wide range of pressures and applied voltages. Basic features of the model will be presented. Temporal evolutions of electrical properties, species densities are presented and discussed. Typical discharge duration of less than 1 ns has been found. The discharge development is characterized by fast propagating waves of ions and electrons, as well as pronounced deviation from quasineutrality. The role of various electron production mechanisms is discussed.
Parasitic micro discharges in high voltage apparatus can lead to it destruction. Understanding of discharge phenomena is therefore of a great importance. Discharge behaviour in a micro void, typical defect of XLPE cable, is studied by a numerical model.
Figure 1: Schematic picture of discharge geometry. 2. Brief model description The void is represented by cylindrical filament (Fig.1) with a length d=(3-10µm) and a radius R=d/2, encapsulated between two 1 cm thick XLPE specimens. The model [1] was adopted and extended for analysis. The plasma-chemical model of a discharge in methane or ethylene considers besides the electrons, neutral species and various positive and negative ions. Corresponding reaction rates and transport data were obtained by solution of electron Boltzmann equation. The model includes the surface emission [2] as possible electron production mechanism.
3. Example of results Fig. 2 shows the spatio-temporal evolution of the electron density n e and of the main ion density CH 4 +
in atmospheric pressure methane discharge. Clear differences in the species behaviour are obvious. Detailed explanation and discussion of this and other results of will be given in presentation.
in methane. P=1 bar, U 0 = 20 kV. Cathode z=0, anode z=10 µm 4. Acknowledgement The project is supported by German federal government (BMBF) by grant FKZ 03SF0476A.
[1] M. M. Becker et al., J. Phys. D: Appl. Phys.
[2] L. Niemeyer, IEEE TDEI 2 (1995) 510.
Topic #10 300 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Effect of space charge on electron emission in vacuum
B. Seznec 1,2 , U Ph. Dessante 2 , Ph. Teste 2 , T. Minea 1
1 P
Saclay, Orsay CEDEX, 91405, France 2
Sorbonne Universités, UPMC Univ Paris 06, Université Paris-Saclay, 91192 Gif sur Yvette CEDEX, France
Vacuum electron sources exploiting field emission are generally operated in direct current (DC) mode. The development of nanosecond pulsed power supplies facilitates the emission of high density electron bunches. The breakdown levels are taken as the highest value of the voltage avoiding the thermo-emission instability. However, the space charge limits the performance of these electron sources by decreasing the electric field and consequently the thermo-field emission at the surface of the electrode. A comparative study of the space charge effect for different protrusions, operated in DC and pulsed modes for a given voltage, shows the decrease of the electron current by a factor of 2 with respect to its value in vacuum (no charge).
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