Browsing by Author "Brinkmann, Ralf Peter"

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    Modelling of a miniature microwave driven nitrogen plasma jet and comparison to measurements
    (Bristol : IOP Publ., 2021) Klute, Michael; Kemaneci, Efe; Porteanu, Horia-Eugen; Stefanović, Ilija; Heinrich, Wolfgang; Awakowicz, Peter; Brinkmann, Ralf Peter
    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 Pa and a gas temperature of Tg = 650–1600 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 coupling in the absorbed power is analyzed. This leads to the interpretation of the discharge regime at an electron density of ne ≈ 6.4 × 1018 m−3 as E/H-hybridmode with an capacitive and inductive component.
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    On the justification of the Poisson-Boltzmann equation in the context of technological plasmas
    (Bristol : IOP Publ., 2021) Köhn, Kevin; Krüger, Dennis; Kemaneci, Efe; Xu, Liang; Eremin, Denis; Brinkmann, Ralf Peter
    The Poisson-Boltzmann (PB) equation is a nonlinear differential equation for the electric potential that describes equilibria of conducting fluids. Its standard justification is based on a variational principle which characterizes the thermodynamic equilibrium of a system in contact with a heat reservoir as a minimum of the Helmholtz free energy. The PB equation is also employed in the context of technological plasmas. There, however, the standard justification is inapplicable: technological plasmas are neither in thermodynamic equilibrium nor in contact with heat reservoirs. This study presents an alternative variational principle which is based on the functionals of entropy, particle number, and electromagnetic enthalpy. It allows to justify the PB equation for a wide class of technological plasmas under realistic assumptions.
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    Simulation and modeling of radio-frequency atmospheric pressure plasmas in the non-neutral regime
    (Bristol : IOP Publ., 2022) Klich, Maximilian; Wilczek, Sebastian; Donkó, Zoltán; Brinkmann, Ralf Peter
    Radio-frequency-driven atmospheric pressure plasma jets (RF APPJs) play an essential role in many technological applications. This work studies the characteristics of these discharges in the so-called non-neutral regime where the conventional structure of a quasi-neutral bulk and an electron depleted sheath does not develop, and the electrons are instead organized in a drift-soliton-like structure that never reaches quasi-neutrality. A hybrid particle-in-cell/Monte Carlo collisions (PIC/MCC) simulation is set up, which combines a fully kinetic electron model via the PIC/MCC algorithm with a drift-diffusion model for the ions. In addition, an analytical model for the electron dynamics is formulated. The formation of the soliton-like structure and the connection between the soliton and the electron dynamics are investigated. The location of the electron group follows a drift equation, while the spatial shape can be described by Poisson-Boltzmann equilibrium in a co-moving frame. A stability analysis is conducted using the Lyapunov method and a linear stability analysis. A comparison of the numerical simulation with the analytical models yields a good agreement.
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    Theoretical investigation of a miniature microwave driven plasma jet
    (Bristol : IOP Publ., 2020) Klute, Michael; Porteanu, Horia-Eugen; Stefanovic, Ilija; Heinrich, Wolfgang; Awakowicz, Peter; Brinkmann, Ralf Peter
    Radio frequency driven plasma jets are compact plasma sources which are used in many advanced fields such as surface engineering or biomedicine. The MMWICP (miniature micro wave ICP) is a particular variant of that device class. Unlike other plasma jets which employ capacitive coupling, the MMWICP uses the induction principle. The jet is integrated into a miniature cavity structure which realizes an LC-resonator with a high quality factor. When excited at its resonance frequency, the resonator develops a high internal current which—transferred to the plasma via induction—provides an efficient source of RF power. This work presents a theoretical model of the MMWICP. The possible operation points of the device are analyzed. Two different regimes can be identified, the capacitive E-mode with a plasma density of ne ≈ 5 × 1017 m−3, and the inductive H-mode with densities of ne ⩾ 1019 m−3. The E to H transition shows a pronounced hysteresis behavior.
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    Zero-dimensional and pseudo-one-dimensional models of atmospheric-pressure plasma jets in binary and ternary mixtures of oxygen and nitrogen with helium background
    (Bristol : IOP Publ., 2021) He, Youfan; Preissing, Patrick; Steuer, David; Klich, Maximilian; Schulz-von der Gathen, Volker; Böke, Marc; Korolov, Ihor; Schulze, Julian; Guerra, Vasco; Brinkmann, Ralf Peter; Kemaneci, Efe
    A zero-dimensional (volume-averaged) and a pseudo-one-dimensional plug-flow (spatially resolved) model are developed to investigate atmospheric-pressure plasma jets operated with He, He/O2, He/N2 and He/N2/O2 mixtures. The models are coupled with the Boltzmann equation under the two-term approximation to self-consistently calculate the electron energy distribution function. An agreement is obtained between the zero-dimensional model calculations and the spatially averaged values of the plug-flow simulation results. The zero-dimensional model calculations are verified against spatially resolved simulation results and validated against a wide variety of measurement data from the literature. The nitric oxide (NO) concentration is thoroughly characterized for a variation of the gas mixture ratio, helium flow rate and absorbed power. An 'effective' and a hypothetical larger rate coefficient value for the reactive quenching N2(A3Σ, B3Π) + O(3P) → NO + N(2D) are used to estimate the role of the species N2(A3Σ, B3Π; v > 0) and multiple higher N2 electronically excited states instead of only N2(A3Σ, B3Π; v = 0) in this quenching. The NO concentration measurements at low power are better and almost identically captured by the simulations using the 'effective' and hypothetical values, respectively. Furthermore, the O(3P) density measurements under the same operation conditions are also better predicted by the simulations adopting these values. It is found that the contribution of the vibrationally excited nitrogen molecules N2(v ≥ 13) to the net NO formation rate gains more significance at higher power. The vibrational distribution functions (VDFs) of molecular oxygen O2(v < 41) and nitrogen N2(v < 58) are investigated regarding their formation mechanisms and their responses to the variation of operation parameters. It is observed that the N2 VDF shows a stronger response than the O2 VDF. The sensitivity of the simulation results with respect to a variation of the VDF resolutions, wall reaction probabilities and synthetic air impurity levels is presented. The simulated plasma properties are sensitive to the variation, especially for a feed gas mixture containing nitrogen. The plug-flow model is validated against one-dimensional experimental data in the gas flow direction, and it is only used in case an analysis of the spatially resolved plasma properties inside the jet chamber is of interest. The increasing NO spatial concentration in the gas flow direction is saturated at a relatively high power. A stationary O2 VDF is obtained along the direction of the mass flow, while a continuously growing N2 VDF is observed until the jet nozzle.