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obtained. Recently, a novel approach to treat many-body Coulomb effects in low-ionization degree gas discharge plasmas has been developed which combines the molecular dynamics description of many-body interactions between electrons and Monte Carlo type description of collision processes between electrons and the background gas. This approach eliminates the need for a binary collision approximation of Coulomb collisions that has been present in all previous Monte Carlo transport simulations as well as in solutions of the Boltzmann equation.
Strongly coupled plasmas. – In contrast to gas discharges, strongly coupled plasmas are systems of charged particles, where the long-ranged electrostatic interaction between charges dominates the dynamics over the thermal motion of the particles. Such plasmas are realized in dense astrophysical objects, cold ion traps, charged colloidal suspensions, and, our system of interest, dusty plasmas. Dusty plasmas are gas discharges with micron-sized solid grains immersed into it. In this case, the grains charge up in the discharge plasma and become trapped in the electric field present in the discharge. As the dynamics of the dust grains and the gas discharge have very different characteristic time scales, the ensemble of charged dust grains can be treated independently of the discharge. The dust component can be well approximated with the one-component plasma model featuring screened Coulomb (Yukawa) inter-particle interactions. The dust grains tend to form crystalline solid or liquid structures, resulting in a model system ideal to study classical phenomena in condensed matter on the particle level. Recently, we have developed a molecular dynamics method to compute the linear and quadratic density-response functions of strongly-coupled Yukawa liquids. The agreement between the results obtained from this approach and from the Fluctuation-Dissipation Theorem (FDT) in the linear regime has verified our computational methods. Based on this, the agreement in the quadratic case has provided a support for the validity of the quadratic FDT that has not been tested so far for similar physical systems.
Dusty plasmas. — They are special manifestations of strongly-coupled plasmas where micrometer-sized solid particles are immersed into a low-pressure gas discharge. These dust grains acquire high electric charge and form a strongly interacting ensemble, which behaves qualitatively similar to classical atomic matter (solids and liquids). Due to their characteristic time and distance scales, these systems can easily be observed on the individual particle level and thus give insight into the microscopic details of well-known macroscopic processes. This time, we have used our dusty-plasma experiment to identify the microphysics behind the slow plastic deformation (creep) that happens due to a constant homogen-eous shearing force. We have observed the creation of pairs of oppositely Figure 1. Defect maps of subsequent system
snapshots from the experiment. Colors lighten with elapsing time. particles with 7 neighbors; particles with 5 neighbors.
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oriented dislocations (see Fig. 1), the rapid (supersonic) glide motion and annihilation of these dislocations at domain walls as being the dominant microphysical processes.
Discharge plasmas for biomedicine. — In the field of biomedicine, we aim to contribute to the understanding of the effect of discharge plasmas on the wound-healing process. In the last decade, it has been found that the direct treatment of wounds by discharge plasmas can accelerate the healing process. In order to understand this effect (that is, the interaction of plasma species with the skin cells) we treated keratinocyte cells with an atmospheric pressure plasma source called plasma needle (the plasma is generated at the tip of a needle as shown in Fig. 2.) and followed the cell proliferation. The wound has been modeled with a scratch made on the cell culture. The cells attached to the bottom of the plate are covered with phosphate buffered saline solution (PBS) during treatment (as shown in Fig. 2.a.) in order not to dry out. We managed to find treatment conditions, related to the discharge input power, treatment time and volume of PBS that covers the cells, where a positive effect on the cell proliferation can be achieved. A maximum in the scratch closing is observed both in function of input power (around 20 W) and treatment time (around 10 s).
In order to clarify these relations further experiments will be conducted. The interaction of the plasma species with the cell medium and the cells is very complex. We are developing plasma and liquid diagnostics, which drive us closer to the understanding of plasma and liquid chemistry of the system.
Figure 2.a. Schematic presentation of the plasma source
“plasma needle” used for cell treatment. Figure 2.b. The structure of the visible glow of the plasma needle.
Analytical plasmas: Electrolyte cathode atmospheric pressure glow discharge (ELCAD). — The most powerful multi-purpose material analysis techniques are based on the light emission spectra, unique to excited chemical elements and molecules. The ELCAD technique is useful to analyze liquid samples, as the cathode of the atmospheric glow discharge is the liquid itself. As result of sputtering and evaporation of the liquid, the chemicals penetrate into the discharge plasma, where the excitation due to electron collisions drives the emission of light. High-resolution spectral analysis results in the detection and identification of trace elements down to the ppm level even in industrial environment, including waste water monitoring. During the last year an electrolyte cathode atmospheric glow discharge atomic emission spectrometry (ELCAD-AES) method was developed for the detection of the industrially relevant In, Rh and Te in water samples. The method uses analytical lines in the
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UV-VIS spectrum, free from spectral overlap interferences, and sensitive enough for quantifying the analytes at mg L-1 or lower levels. The studies conducted have shown that the detection of Te and Rh is very difficult, the emission intensities of interference-free transitions are very low. The emission intensities are highly sample pH dependent; that is, analytical signals can only be detected at pHs lower than 2. However, the use of acidity lower than pH 1 causes lower plasma volume; that is, the contraction of plasma into the sample introduction capillary creating discharge instabilities resulting in frequent self-extinction. The detection limits for In, Rh, and Te were found to be 0.01, 0.5, and 2.4 mg L-1, respectively, while the precision expressed as relative standard deviation (RSD) not higher than 4.6, 6.4, and 7.4 %, respectively. Samples with high salt content (for example, well water) caused positive matrix effects (1.4 - 3.2-fold signal enhancements), but also approx.
1.5-times higher RSDs.
Grants
OTKA K-105476: High performance modelling and simulation of low-temperature and strongly coupled plasmas (Z. Donkó, 2013-2016)
OTKA NN 103150: Dusty plasma: a laboratory for classical many-particle physics (P.
Hartmann, 2012-2015)
OTKA K 104531: High and low-frequency discharges for biomedical applications and nanostructuring (K. Kutasi, 2012-2016)
COST Action MP1101 Biomedical Applications of Atmospheric Pressure Plasma Technology (Management Committee Member: K. Kutasi 2012-2015)
COST Action TD1208 Electrical discharges with liquids for future applications (Management Committee Members: K. Kutasi, I. Korolov 2013-2016)
“Wigner research group” support
International cooperation
Boston College
Ruhr Universität Bochum Baylor University Texas
Institute of Physics Belgrade (Belgrade, Serbia), Interaction of discharge plasmas with living cells (Zoran Lj. Petrovic, Nevena Puac)
Josef Stefan Institute Ljubljana (Ljubljana, Slovenia), Surface treatments in afterglow plasmas (Miran Mozetic)
Institut Jean Lamour École des Mines Nancy (Nancy, France), Gabriel Lippmann Centre Luxembourg (Luxembourg) Elementary processes in afterglow plasmas (Thierry Belmonte, David Duday)
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Publications
Articles
1. Derzsi A, Kovács AZs, Donkó Z, Hartmann P: On the metastability of the hexatic phase during the melting of two-dimensional charged particle solids. PHYS PLASMAS, 21:(2) Paper 023706. 6 p. (2014)
2. Donkó Z: First principles calculation of the effect of Coulomb collisions in partially ionized gases. PHYS PLASMAS, 21:(4) Paper 043504. 6 p. (2014)
3. Dzhumagulova KN, Masheeva RU, Ramazanov TS, Donkó Z: Effect of magnetic field on the velocity autocorrelation and the caging of particles in two-dimensional Yukawa liquids. PHYS REV E, 89:(3) Paper 033104. 7 p. (2014)
4. Hartmann P, Kovacs AZ, Reyes JC, Matthews LS, Hyde TW: Dust as probe for horizontal field distribution in low pressure gas discharges. PLASMA SOURCES SCI T, 23:(4) Paper 045008. 7 p. (2014)
5. Hartmann P, Kovács AZ, Douglass AM, Reyes JC, Matthews LS, Hyde TW: Slow plastic creep of 2D dusty plasma solids. PHYS REV LETT, 113:(2) Paper 025002. 5 p. (2014) 6. Hartmann P, Donkó Z, Rosenberg M, Kalman GJ: Waves in two-dimensional
superparamagnetic dusty plasma liquids. PHYS REV E, 89:(4) Paper 043102. 9 p. (2014) 7. Iwashita S, Schungel E, Schulze J, Hartmann P, Donko Z, Uchida G, Koga K, Shiratani M,
Czarnetzki U: Dust hour glass in a capacitive RF discharge. IEEE T PLASMA SCI, 42:(10) pp. 2672-2673. (2014)
8. Kalman GJ, Donkó Z, Hartmann P, Golden KI: Second plasmon and collective modes in binary Coulomb systems. EUROPHYS LETT, 107:(3) Paper 35001. 6 p. (2014)
9. Korolov I, Derzsi A, Donko Z: Experimental and kinetic simulation studies of radio-frequency and direct-current breakdown in synthetic air. J PHYS D APPL PHYS, 47:(47) Paper 475202. 9 p. (2014)
10. Kutasi K, Zaplotnik R, Primc G, Mozetic M: Controlling the oxygen species density distributions in the flowing afterglow of O2/Ar-O2 surface-wave microwave discharges.
J PHYS D-APPL PHYS, 47:(2) Paper 025203. (2014)
11. Magyar P, Donko Z, Kalman GJ, Golden KI: Linear and quadratic static response functions and structure functions in Yukawa liquids. PHYS REV E, 90:(2) Paper 023102.
10 p. (2014)
12. Rosenberg M, Kalman GJ, Hartmann P, Goree J: Effect of strong coupling on the dust acoustic instability. PHYS REV E, 89:(1) Paper 013103. (2014)
13. Schulze J, Schungel E, Derzsi A, Korolov I, Mussenbrock T, Donko Z: Complex electron heating in capacitive multi-frequency plasmas. IEEE T PLASMA SCI, 42:(10) pp. 2780-2781. (2014)
14. Vesel A, Kolar M, Recek N, Kutasi K, Stana-Kleinschek K, Mozetic M: Etching of blood
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proteins in the early and late flowing afterglow of oxygen plasma. PLASMA PROCESS POLYM, 11:(1) pp. 12-23. (2014)
Conference proceedings
15. Hartmann P, Kovács AZs, Donkó Z: Poros plazma: az erősen csatolt rendszerek laboratóriuma (Dusty plasma: laboratory of strongly coupled systems, in Hungarian).
In: Kvantumelektronika 2014: Proc. of the VII. Symposium on the results of domestic quantum-electronics research. Budapest, 28.11.2014, Eds.: Ádám P, Almási G, University of Pécs, Hungary, 2014. Paper E7. 2 p.
16. Korolov I, Derzsi A, Donkó Z: Electric breakdown in synthetic air in the radiofrequency domain. In: Kvantumelektronika 2014: Proc. of the VII. Symposium on the results of domestic quantum-electronics research. Budapest, 28.11.2014, Eds.: Ádám P, Almási G, University of Pécs, Hungary, 2014. Paper P68. 2 p.
17. Kovács AZs, Hartmann P, Donkó Z: Dinamikus viszkozitás kétdimenziós komplex plazmában (Dynamic viscosity in two-dimensional complex plasmas, in Hungarian). In:
Kvantumelektronika 2014: Proc. of the VII. Symposium on the results of domestic quantum-electronics research. Budapest, 28.11.2014, Eds.: Ádám P, Almási G, University of Pécs, Hungary, 2014. Paper P69. 2 p.
18. Kutasi K: Rezonátor-lengési spektroszkópia (Resonator swinging spectroscopy). In: Az ELI-APS felépítése, lehetőségei és alkalmazási perspektivái (Structure, possibilities and application perspectives of ELI-ALPS), Kecskemét, Hungary, 05.12.2014, Eds.: Veres M, Borossáné Toth S, Nagyné Szokol Á, College of Kecskemét, 2014.pp. 68-75.
19. Magyar P, Korolov I, Donkó Z: Franck-Hertz kísérlet: 100 éve és ma (The Franck-Hertz experiment: 100 years ago and today, in Hungarian). In: Kvantumelektronika 2014:
Proc. of the VII. Symposium on the results of domestic quantum-electronics research.
Budapest, 28.11.2014, Eds.: Ádám P, Almási G, University of Pécs, Hungary, 2014.
Paper P70. 2 p.
Other
20. Donkó Z, Korolov I, Magyar P: Franck-Hertz-kísérlet: 100 éve és ma (The Franck-Hertz experiment: 100 years ago and today, in Hungarian). FIZIKAI SZEMLE, 64:(4) pp. 125-131. (2014)
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