arXiv subjects

Peter Awakowicz

Publications and source records attributed to Peter Awakowicz.

At least 19 recordsLinked to original sources

arXiv2025

Characterization of a laser filament-induced plasma in air at 10 kHz using optical emission spectroscopy

The increasing availability of high-power Yb-based ultrafast laser-amplifier systems has opened the possibility of air filamentation at high repetition rates >1 kHz. In this new regime, accumulation effects cannot be ruled out, therefore, characterizing the plasma parameters and afterglow plasma-chemical kinetics becomes increasingly relevant. In this work, we use optical emission spectroscopy to measure nanosecond dynamics of gas temperature and electron temperature, species-specific decay times, and electron density of an atmospheric air laser filament produced by high average power femtosecond laser at a high repetition rate of 10 kHz. The molecular excitation mechanisms behind the nitrogen photoemissions are derived from vibrational distributions and temporal behavior of the studied emission bands. The presented diagnostic technique offers a complementary but more holistic measurement approach to optical probe schemes to characterize the laser-filament-induced plasma wake for high repetition rate filaments.

physics.plasm-ph↗

arXiv2025

Electron and gas temperature-driven chemistry during microdischarges formed in water vapour bubbles

Microdischarges formed in bubbles immersed in liquids are of interest for materials synthesis and chemical conversion applications in the frame of plasma-driven electrochemistry. A key challenge associated with controlling such processes is the limited understanding of the gas-phase chemical kinetics in these microdischarges. Due to their large electron densities, and high gas temperatures, both electron and gas temperature driven chemistry are likely to be important. Here, a 0-D modelling approach, informed by experimental measurements, is used to study the chemical kinetics in these systems. A new reaction scheme is developed for microdischarges in water vapour, including reactions for both high electron density, and high gas temperature regimes. Microdischarges formed during plasma electrolytic oxidation are used as a test case, however, the key results are expected to be transferable to other plasma electrolysis systems with similar properties. Experimentally measured power densities are used as input to the 0-D model, together with estimates of temperatures and gas pressures within the gas bubble. Comparison of measured and simulated electron densities shows good agreement, given the limitations of both model and experiment. In the base case microdischarge, H$_{2}$O is found to be highly dissociated during the period of peak power density, with H and O making up the majority of the neutral gas in the bubble. The maximum ionization degree is around 0.31$\,\%$, and the electronegativity during the period of peak electron density is found to be low. Species formation and reaction pathways are analysed under variation of the neutral gas temperature from 2000$\,$K to 6000$\,$K. At all temperatures, electron, ion, and neutral reactions with high threshold energies are found to be important for the overall chemical kinetics.

physics.plasm-ph↗

arXiv2025

Characterisation of single microdischarges during plasma electrolytic oxidation of aluminium and titanium

Plasma electrolytic oxidation (PEO) is a technique used to create oxide-ceramic coatings on lightweight metals, such as aluminium, magnesium, and titanium. PEO is known for producing coatings with high corrosion resistance and strong adhesion to the substrate. The process involves generating short-lived microdischarges on the material surface through anodic dielectric breakdown in a conductive aqueous solution. To investigate single microdischarges during PEO, a single microdischarge setup was developed, where the active anode surface is reduced to the tip of a wire with a diameter of 1 mm. In this work the focus is on the effect of electrolyte concentration, anode material, and electrical parameters on the microdischarges. The electrolyte is composed of distilled water with varying concentrations of potassium hydroxide (0.5 - 4 g/l). High-speed optical measurements are conducted to gain insights into the formation and temporal evolution of individual microdischarges and the induced gas bubble formation. Optical emission spectroscopy is used to estimate surface and electron temperatures by fitting Bremsstrahlung and Planck's law to the continuum spectrum of the microdischarges. To evaluate the impact of the microdischarges on coating morphology, the resulting oxide layers on the metal tips are analysed using scanning electron microscopy. The study demonstrates that microdischarge behaviour is significantly influenced by the substrate material, treatment time, and electrolyte concentration, all of which impact the coating morphology. Under the conditions studied in this work, aluminium exhibits longer microdischarge and bubble lifetimes, with fewer cracks on the top layer of the coating, whereas titanium showed faster, shorter-lived bubbles due to more rapid microdischarge events.

physics.plasm-ph↗

arXiv2025

Overcoming Discharge Inhibition in n-Butane Oxidation: Two-Component BaTiO3 and Mn-Cu Mixed Oxide Coatings

A twin surface dielectric barrier discharge on the microsecond scale was used in combination with a two-component coating to oxidize 300 ppm n-butane as a model volatile organic compound to CO2 and H2O in synthetic air at room temperature and at 160 {\deg}C. The integration of BaTiO3 as a base material for the coating allowed the successful use of otherwise discharge-ignition-inhibiting materials such as MnO2-CuO applied as a full coating. Application of pure BaTiO3 led to highly porous coatings that do not hinder the discharge ignition and show a negligible influence on n-butane conversion while reducing byproduct formation. Thus, BaTiO3 was identified as a suitable structure-directing agent in two-component coatings, using 1:1 and 1:2 ratios of BaTiO3:catalyst coatings. Coated electrode configurations were compared to their respective uncoated state to highlight the coating-induced changes. The two-component coatings strongly increased the CO2 selectivity, reaching a maximum of 91.6 % at an energy density of 450 J/L and 160 {\deg}C for the 1:2 ratio, corresponding to an increase of 51.0 % relative to the uncoated electrode.

physics.plasm-ph↗

arXiv2024

Decoupling NO production and UV emission intensity over the E-H mode transition in a low-pressure inductively coupled plasma device

A low-pressure double-inductively coupled plasma device is used to study the fundamental plasma parameters, plasma chemistry, and UV photon emission from the first excited state of nitric oxide, NO(A), in gas mixtures of nitrogen and oxygen. In addition to the gas mixture, rf power and gas pressure are varied, and the E-H mode transition of the inductively coupled plasma is studied specifically. The gas temperature and UV photon emission are measured by optical emission spectroscopy (OES), the absolute density of the nitric oxide electronic ground state by laser-induced fluorescence (LIF), as well as electron density and electron temperature by a multipole resonance probe (MRP). A simple collisional-radiative model for UV emission from NO(A) is developed, which takes the measured densities of ground state nitric oxide and electrons, as well as the electron temperature and neutral gas temperature, as input parameters. The results reveal the links between the absolute densities of ground state nitric oxide, the excitation of this species driven by electron impact and collisions with nitrogen metastables, quenching of the nitrogen metastables, and the resulting UV photon emission rate. The density of ground state nitric oxide is shown to increase with power, while the discharge remains in E-mode, and to decrease significantly with the transition into H-mode, when sufficient rf power is deposited in the discharge. Despite the lower densities of ground state nitric oxide in H-mode, the UV photon emission intensity increases continuously with higher rf powers and over the E-H transition. This effect is shown to be caused by increased excitation of NO(A) by nitrogen metastables in H-mode, which is sufficient to overcompensate the decrease in ground state nitric oxide density.

physics.plasm-ph↗

arXiv2024

The role of flow field dynamics in enhancing volatile organic compound conversion in a surface dielectric barrier discharge system

This study investigates the correlation between flow fields induced by a surface dielectric barrier discharge (SDBD) system and its application for the volatile organic compound (VOC) gas conversion process. As a benchmark molecule, the conversion of n-butane is monitored using flame ionization detectors, while the flow field is analysed using planar particle image velocimetry. Two individual setups are developed to facilitate both conversion measurement and investigation of induced fluid dynamics. Varying the gap distance between two SDBD electrode plates for three different n-butane mole fractions reveals local peaks in relative conversion around gap distances of 16 mm to 22 mm, indicating additional spatially dependent effects. The lowest n-butane mole fractions exhibit the highest relative conversion, while the highest n-butane mole fraction conversion yields the greatest number of converted molecules per unit time. Despite maintaining constant energy density, the relative conversion exhibits a gradual decrease with increasing distances. The results of the induced flow fields reveal distinct vortex structures at the top and bottom electrodes, which evolve in size and shape as the gap distances increase. These vortices exhibit gas velocity magnitudes approximately seven times higher than the applied external gas flow velocity. Vorticity and turbulent kinetic energy analyses provide insights into these structures' characteristics and their impact on gas mixing. A comparison of line profiles through the centre of the vortices shows peaks in the middle gap region for the same gap distances, correlating with the observed peaks in conversion. These findings demonstrate a correlation between induced flow dynamics and the gas conversion process, bridging plasma actuator studies with the domain of chemical plasma gas conversion.

physics.plasm-ph↗

arXiv2024

Numerical investigation of vacuum ultra-violet emission in Ar/O$_2$ inductively coupled plasmas

Controlling fluxes of vacuum ultraviolet (VUV) radiation is important in a number of industrial and biomedical applications of low pressure plasma sources because, depending on the process, VUV radiation may be desired, required to a certain degree, or unwanted. In this work, the emission of VUV radiation from O atoms is investigated in low-pressure Ar/O$_2$ inductively coupled plasma via numerical simulations. For this purpose, a self-consistent Ar/O$_2$ plasma-chemical reaction scheme has been implemented in a zero dimensional plasma chemical kinetics model and is used to investigate VUV emission from excited O atoms (3s $^5$S$^0_2$) and 3s $^3$S$^0_1$) at 130 and 135 nm. The model is extensively compared with experimental measurements of absolute VUV emission intensities, electron densities and Ar excited state densities. In addition, VUV emission intensities are investigated as a function of pressure, Ar/O$_2$ mixture, and power deposition and the dominant reaction pathways leading to VUV emission are identified and described. In general terms, absolute VUV emission intensities increase with power and oxygen fraction over the ranges investigated and peak emission intensities are found for pressures between 5-50 Pa. The emission is dominated by the 130 nm resonance line from the decay of the O(3s $^3$S$^0_1$) state to the ground state. Besides, at low pressure (0.3-1 Pa), the flux of VUV photons to surfaces is much lower than that of positive ions, whereas VUV fluxes dominate at higher pressure, $\gtrsim$5-50 Pa depending on O$_2$ fraction. Finally, oxygen atom fluxes to surfaces are, in general, larger than those of VUV photons for the parameter space investigated.

physics.plasm-ph↗

arXiv2023

Interactions between flow fields induced by surface dielectric barrier discharge arrays

This study investigates the flow field induced by a surface dielectric barrier discharge (SDBD) system, known for its efficient pollution remediation of volatile organic compounds (VOCs). We aim to understand the flow dynamics that contribute to the high conversion observed in similar systems. Experimental techniques, including schlieren imaging and particle image velocimetry (PIV), applied with high temporal resolution, were used to analyse the flow field. Complementary, fluid simulations are employed to investigate the coupling between streamer and gas dynamics. Results show distinct fluid field behaviours for different electrode configurations, which differ in geometric complexity. The fluid field analysis of the most basic electrode design revealed behaviours commonly observed in actuator studies. The simulation results indicate the local information about the electron density as well as different temporal phases of the fluid flow. The electrode design with mostly parallel grid line structures exhibits confined vortices near the surface. In contrast, an electrode design also used in previous studies, is shown to promote strong gas transport through extended vortex structures, enhancing gas mixing and potentially explaining the high conversion observed.

physics.plasm-ph↗

arXiv2023

PECVD and PEALD on polymer substrates (Part II): Understanding and tuning of barrier and membrane properties of thin films

This feature article presents insights concerning the correlation of PECVD and PEALD thin film structures with their barrier or membrane properties. While in principle similar precursor gases and processes can be applied, the adjustment of deposition parameters for different polymer substrates can lead to either an effective diffusion barrier or selective permeabilities. In both cases the understanding of the film growth and the analysis of the pore size distribution and the pore surface chemistry is of utmost importance for the understanding of the related transport properties of small molecules. In this regard the article presents both concepts of thin film engineering and analytical as well as theoretical approaches leading to a comprehensive description of the state of the art in this field. Moreover, based on the presented correlation of film structure and molecular transport properties perspectives of future relevant research in this area is presented.

cond-mat.soft↗

arXiv2023

PECVD and PEALD on polymer substrates (part I): Fundamentals and analysis of plasma activation and thin film growth

This feature article considers the analysis of the initial states of film growth on polymer substrates. The assembled results are based on the cooperation between research groups in the field of plasma physics, chemistry, electric as well as mechanical engineering over the last years, mostly within the frame of the transregional project SFB-TR 87 ("Pulsed high power plasmas for the synthesis of nanostructured functional layers"). This feature article aims at bridging the gap between the understanding of plasma processes in the gas phase and the resulting surface and interface processes of the polymer. The results show that interfacial adhesion and initial film growth can be well controlled and even predicted based on the combination of analytical approaches.

cond-mat.soft↗

arXiv2022

Electron dynamics in planar radio frequency magnetron plasmas: III. Comparison of experimental investigations of power absorption dynamics to simulation results

In magnetized capacitively coupled radio-frequency discharges operated at low pressure the influence of the magnetic flux density on discharge properties has been studied recently both by experimental investigations and in simulations. It was found that the Magnetic Asymmetry Effect allows for a control of the DC self-bias and the ion energy distribution by tuning the magnetic field strength. In this study, we focus on experimental investigations of the electron power absorption dynamics in the presence of a magnetron-like magnetic field configuration in a low pressure capacitive RF discharge operated in argon. Phase Resolved Optical Emission Spectroscopy measurements provide insights into the electron dynamics on a nanosecond-timescale. The magnetic flux density and the neutral gas pressure are found to strongly alter these dynamics. For specific conditions energetic electrons are efficiently trapped by the magnetic field in a region close to the powered electrode, serving as the target surface. Depending on the magnetic field strength an electric field reversal is observed that leads to a further acceleration of electrons during the sheath collapse. These findings are supported by 2-dimensional Particle in Cell simulations that yield deeper insights into the discharge dynamics.

physics.plasm-ph↗

arXiv2022

Electron dynamics in planar radio frequency magnetron plasmas: I. The mechanism of Hall heating and the {\mu}-mode

The electron dynamics and the mechanisms of power absorption in radio-frequency (RF) driven, magnetically enhanced capacitively coupled plasmas (MECCPs) at low pressure are investigated. The device in focus is a geometrically asymmetric cylindrical magnetron with a radially nonuniform magnetic field in axial direction and an electric field in radial direction. The dynamics is studied analytically using the cold plasma model and a single-particle formalism, and numerically with the inhouse energy and charge conserving particle-in-cell/Monte Carlo collisions code ECCOPIC1S-M. It is found that the dynamics differs significantly from that of an unmagnetized reference discharge. In the magnetized region in front of the powered electrode, an enhanced electric field arises during sheath expansion and a reversed electric field during sheath collapse. Both fields are needed to ensure discharge sustaining electron transport against the confining effect of the magnetic field. The corresponding azimuthal ExB-drift can accelerate electrons into the inelastic energy range which gives rise to a new mechanism of RF power dissipation. It is related to the Hall current and is different in nature from Ohmic heating, as which it has been classified in previous literature. The new heating is expected to be dominant in many magnetized capacitively coupled discharges. It is proposed to term it the "{\mu}-mode" to separate it from other heating modes.

physics.plasm-ph↗

arXiv2021

Modelling of a miniature microwave driven nitrogen plasma jet and comparison to measurements

The MMWICP (Miniature MicroWave ICP) is a new plasma source using the induction principle. Recently Klute et al. presented a mathematical model for the electromagnetic fields and power balance of the new device. In this work the electromagnetic model is coupled with a global chemistry model for nitrogen, based on the chemical reaction set of Thorsteinsson and Gudmundsson and customized for the geometry of the MMWICP. The combined model delivers a quantitative description for a non-thermal plasma at a pressure of $p=1000\,\mathrm{Pa}$ and a gas temperature of $T_\mathrm{g}=650\mbox{-}1600\,\mathrm{K}$. Comparison with published experimental data shows a good agreement for the volume averaged plasma parameters at high power, for the spatial distribution of the discharge and for the microwave measurements. Furthermore, the balance of capacitive and inductive \linebreak coupling in the absorbed power is analyzed. This leads to the interpretation of the discharge regime at a electron density of $n_\mathrm{e} \approx 6.4 \!\times\!10^{18} \, \mathrm{m}^{-3}$ as $E/H$-hybridmode with an capacitive and inductive component.

physics.plasm-ph↗

arXiv2020

Theoretical investigation of a miniature microwave driven plasma jet

Microwave and radio frequency driven plasmas jets play an important role in many technical applications. They are usually operated in a capacitive mode known as E-mode. As a new plasma source the MMWICP (Miniature Micro Wave ICP) has been proposed, a small scale plasma jet with inductive coupling based on a specially designed resonator that acts as an LC-resonance circuit. This work presents a theoretical model of the new device, based on a series representation of the electromagnetic field in the resonator and the volume integrated (global) model for the loss processes within the plasma. An infinite number of modes can be found ordered by the azimuthal wave number m. These modes essentially determine the electromagnetic behavior of the system and differ from ordinary cavity modes. The mode m=0 can be identified with the inductive mode and is called H-mode, the mode m=1 is the capacitive mode and is called E-mode. Both modes refer to different operating regimes, which are separated by different values of the plasma parameters. In a second step the matching network and its characteristics are taken into account in order to find stable equilibrium points and possible hysteresis effects. As main result, the feasibility of inductive power coupling for the MMWICP resonator is shown.

physics.plasm-ph↗

arXiv2020

Inductively Coupled Plasma at Atmospheric Pressure, a Challenge for Miniature Devices

Plasma jets belong to the category remote plasma. This means that the discharge conditions and the chemical effect on samples can be tuned separately, this being a big advantage compared to standard low-pressure reactors. The inductive coupling brings the advantage of a pure and dense plasma. The microwave excitation allows furthermore miniaturization and generation of low temperature plasmas. The present paper shows the state of the art of the research on such sources, demonstrating their work up to atmospheric pressure.

physics.plasm-ph↗

arXiv2016

A global model of cylindrical and coaxial surface-wave discharges

A volume-averaged global model is developed to investigate surface-wave discharges inside either cylindrical or coaxial structures. The neutral and ion wall flux is self-consistently estimated based on a simplified analytical description both for electropositive and electronegative plasmas. The simulation results are compared with experimental data from various discharge setups of either argon or oxygen, measured or obtained from literature, for a continuous and a pulse-modulated power input. A good agreement is observed between the simulations and the measurements. The calculations show that the wall flux often substantially contributes to the net loss rates of the individual species.

physics.plasm-ph↗

arXiv2012

Characterization of dielectric barrier discharge in air applying current measurement, numerical simulation and emission spectroscopy

Dielectric barrier discharge (DBD) in air is characterized applying current measurement, numerical simulation and optical emission spectroscopy (OES). For OES, a non-calibrated spectrometer is used. This diagnostic method is applicable when cross-sectional area of the active plasma volume and current density can be determined. The nitrogen emission in the spectral range of 380 nm- 406 nm is used for OES diagnostics. Electric field in the active plasma volume is determined applying the measured spectrum, well-known Frank-Condon factors for nitrogen transitions and numerically- simulated electron distribution functions. The measured electric current density is used for determination of electron density in plasma. Using the determined plasma parameters, the dissociation rate of nitrogen and oxygen in active plasma volume are calculated, which can be used by simulation of the chemical kinetics.

physics.plasm-ph↗

arXiv2011

Space-resolved characterization of high frequency atmospheric-pressure plasma in nitrogen applying optical emission spectroscopy and numerical simulation

Averaged plasma parameters such as electron distribution function and electron density are determined by characterization of high frequency (2.4 GHz) nitrogen-plasma using both experimental methods, namely optical emission spectroscopy (OES) and microphotography, and numerical simulation. Both direct and stepwise electron-impact excitation of nitrogen emissions are considered. The determination of space-resolved electron distribution function, electron density, rate constant for electron-impact dissociation of nitrogen molecule and the production of nitrogen atoms, applying the same methods, is discussed. Spatial distribution of intensities of neutral nitrogen molecule and nitrogen molecular ion from the microplasma is imaged by a CCD camera. The CCD images are calibrated using the corresponding emissions measured by absolutely-calibrated OES, and are then subjected to inverse Abel transformation to determine space-resolved intensities and other parameters. The space-resolved parameters are compared, respectively, with the averaged parameters, and an agreement between them is established.

physics.plasm-ph↗