Low-pressure inductively coupled plasma (ICP) is promising for space electric propulsion. For the first time, an implicit electromagnetic particle-in-cell Monte Carlo collision model based on the alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is developed to investigate low-pressure xenon plasma characteristics of a miniature ICP source. The induced simulated electric field is well consistent with that calculated by the finite element method, indicating that this method can provide an accurate estimation of the electromagnetic field. The simulation time step used in the ADI-FDTD method is no longer restricted by the Courant–Friedrichs–Lewy constraints. Compared with the FDTD method, the ADI-FDTD method increases the size of the time step and significantly improves computational efficiency. The method is validated by comparing the simulated and measured electron density and plasma potential profile and reasonable agreement is reached. Therefore, the model is used to investigate the temporal and spatial distribution of plasma properties and the influence of the current amplitude of radio frequency (RF) coil, applied frequency of RF coil and neutral gas pressure on the plasma dynamics in the ionization chamber of a miniature gridded RF ion thruster. To explain the influence of the operating parameters, a concept called ‘the energy relaxation characteristics of electrons in response to the change of electric field’ is proposed and verified. The simulations also find that the oscillation frequency of plasma properties is twice the applied frequency of RF coil. The oscillation characteristics reveal the dynamic energy balance in the ICP. The experiment on the gridded RF ion thruster BHRIT-4 confirms the oscillation by measuring the plasma sheath potential.
A. Böddecker, Maximilian Passmann, Angie Natalia Torres Segura
et al.
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 gas conversion process. As a benchmark molecule, the conversion of n-butane is monitored using flame ionization detectors, while the flow field is analyzed 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 16–22 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 intothese structures’ characteristics and their impact on gas mixing. A comparison of line profiles through the center 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.
Jeremy J. Williams, Ashish Bhole, Dylan Kierans
et al.
Understanding plasma instabilities is essential for achieving sustainable fusion energy, with large-scale plasma simulations playing a crucial role in both the design and development of next-generation fusion energy devices and the modelling of industrial plasmas. To achieve sustainable fusion energy, it is essential to accurately model and predict plasma behavior under extreme conditions, requiring sophisticated simulation codes capable of capturing the complex interaction between plasma dynamics, magnetic fields, and material surfaces. In this work, we conduct a comprehensive HPC analysis of two prominent plasma simulation codes, BIT1 and JOREK, to advance understanding of plasma behavior in fusion energy applications. Our focus is on evaluating JOREK's computational efficiency and scalability for simulating non-linear MHD phenomena in tokamak fusion devices. The motivation behind this work stems from the urgent need to advance our understanding of plasma instabilities in magnetically confined fusion devices. Enhancing JOREK's performance on supercomputers improves fusion plasma code predictability, enabling more accurate modelling and faster optimization of fusion designs, thereby contributing to sustainable fusion energy. In prior studies, we analysed BIT1, a massively parallel Particle-in-Cell (PIC) code for studying plasma-material interactions in fusion devices. Our investigations into BIT1's computational requirements and scalability on advanced supercomputing architectures yielded valuable insights. Through detailed profiling and performance analysis, we have identified the primary bottlenecks and implemented optimization strategies, significantly enhancing parallel performance. This previous work serves as a foundation for our present endeavours.
In this study, we introduce a comprehensive numerical framework that integrates transmission line, lumped circuit, and particle-in-cell/Monte Carlo (PIC) models for accurate plasma discharge simulations. Leveraging the Lax-Wendroff method, our approach enables bidirectional coupling between transmission lines, lumped circuits, and PIC models, capturing nonlinear interactions between pulsed power sources and plasma loads. By directly solving transmission line equations, our model enhances fidelity in describing plasma dynamics compared to conventional equivalent circuits. Validation against analytical benchmarks and Simulink results confirms the efficacy of our approach. Through simulations, we elucidate the pulse formation and energy transfer processes in gas discharge phenomena. With this model, we have simulated several gas discharge and plasma sources, including RF gas breakdown, impedance matching of capacitively coupled plasmas, and dielectric barrier discharges. Additionally, our framework exhibits scalability, facilitating its application in diverse discharge scenarios. Furthermore, we extend our investigations to include low-temperature plasma sources, broadening the scope of our research in plasma science and engineering.
This paper presents a self-consistent multi-dimensional mathematical model and a numerical approach for simulating the low-temperature plasma induced by the femtosecond laser filament. Addressing limitations in current models, we analyze key aspects of the laser plasma behavior, including plasma generation, detailed chemical kinetics, energy exchange channels, total energy balance, and hydrodynamics. The developed model and LOTASFOAM code are applied to study the temporal and spatial decay of the plasma produced by a femtosecond laser pulse in pure nitrogen at atmospheric pressure. The paper also includes a discussion on the spatial and temporal dynamics of electronically excited states of nitrogen in the decaying laser plasma.
Due to the high reactivity and the non-thermal properties of streamer discharges, they are applied in various fields, such as water treatment and medicine. Streamer discharges are usually produced in the gas phase before interacting with a liquid or solid surface. Although the dynamics of a streamer discharge in gases is well described, its propagation at liquid surfaces remains poorly understood. In this study, we investigate the influence of water electrical conductivity (σ), between 2 and 1000 µS cm−1, on the characteristics and propagation dynamics of pulsed positive DC nanosecond discharges with the solution serving as a cathode. σ strongly influences τ r (the dielectric relaxation time), and two discharge modes may be obtained, depending on whether τ r is shorter or longer than the delay to achieve breakdown (τ pulse). This latter can be indirectly modified by adjusting the voltage amplitude (V a). In the case of V a = 14 kV, the breakdown voltage (V bd) at low σ is lower than that measured at high σ, probably because τ pulse τ r, respectively. In the case of V a = 20 kV, V bd decreases slightly with σ, probably because of the decrease of the resistivity of the global electrical circuit as τ pulse ∼ τ r for high σ. In addition to the electrical characterization, the dynamics of the discharge at the solution’s surface is investigated using 1 ns-time-resolved imaging. Its morphology was found to evolve from a disc to a ring before it splits into highly organized plasma dots (streamers’ head). The number (N dots) and propagation velocity of plasma dots are determined as a function of σ. At V a = 14 kV, N dots does not vary significantly with σ despite the increase of V bd; this latter likely compensates the neutralization of charge accumulated at the surface by ions in solution. In the case of V a = 20 kV, N dots decreases with σ, and it can be related to a decrease of accumulated charge at the water surface. Finally, based on the electrical measurements, we found that the charge per plasma dot (Q dot) increases with σ, which does not correlate with the imaging results that show a short length of propagation at high σ. Then, considering the plasma dot mobility at low σ and the instantaneous propagation velocities at high σ, a more realistic Q dot is measured.
A chemical kinetics model was developed to characterise the gas‐phase dynamics of H2 production in nanosecond‐pulsed CH4 plasmas. Pulsed behaviour was observed in the calculated electric field, electron temperature and species densities at all pressures. The model agrees reasonably with experimental results, showing CH4 conversion at 30% and C2H2 and H2 as major products. The underlying mechanisms in CH4 dissociation and H2 formation were analysed, highlighting the large contribution of vibrationally excited CH4 and H2 to coupling energy from the plasma into gas‐phase heating, and revealing that H2 synthesis is not affected by applied pressure, with selectivity remaining unchanged at ~42% in the 1–5 bar range.
Abstract Bioactive furanocoumarins, a group of natural secondary metabolites common in higher plants, are recognized for their benefits to human health and have been shown to have numerous biological properties. However, the knowledge of its biomolecular mechanism is not known. One of the main furanocoumarins is bergamottin (BGM), which is characterized by a planar three-ringed structure and a hydrocarbon chain, which give BGM its high lipid/water partition coefficient. Because of that, and although the biological mechanism of BGM is not known, BGM bioactive properties could be ascribed to its potential to interact with the biological membrane, modulating its structure, changing its dynamics and at the same time that it might interact with lipids. For our goal, we have applied molecular dynamics to determine the position of BGM in a complex membrane and discern the possibility of certain interactions with membrane lipids. Our findings establish that BGM tends to locate in the middle of the hydrocarbon layer of the membrane, inserts in between the hydrocarbon chains of the phospholipids in an oblique position with respect to the membrane plane, increasing the fluidity of the membrane. Significantly, BGM tends to be surrounded by POPC molecules but exclude the molecule of CHOL. Outstandingly, BGM molecules associate spontaneously creating aggregates, which does not preclude them from interacting with and inserting into the membrane. The bioactive properties of BGM could be ascribed to its membranotropic effects and support the improvement of these molecules as therapeutic molecules, giving place to new opportunities for potential medical improvements. Communicated by Ramaswamy H. Sarma
This study presents a general methodology and an experimental approach to identify the gas components within laser-induced cavitation bubbles. A needle electrode inside the cavitation bubble, which introduces low electric energy into the bubble, produces a homogenous plasma discharge inside the vapor cavity. The primary bubble dynamics remain identical while the rebound bubble becomes about twice as large when a discharge is applied. The effect of non-condensable gases and the electric charge on bubble dynamics is explored theoretically, and the role of the electric charge is found to be significant. Optical emission spectroscopy reveals the evolution of emission lines from gases inside bubbles. H lines and OH lines are persistently observed in all cases, providing a dominant presence of water vapor. The results also confirm that the gases, which are initially present in the water rather than transported from the water, contribute to the optical emission characteristics with different dissolved gases.
Abstract A concise overview of the vibrational model of heat transfer in simple fluids with soft pairwise interactions is presented. The model is applied to evaluate the thermal conductivity coefficient of the strongly coupled Yukawa fluid, which often serves as a simplest model of a real liquid-like dusty (complex) plasma. A reasonable agreement with the available data from molecular dynamics numerical simulations is observed. Universality of the properly reduced thermal conductivity coefficient with respect to the effective coupling parameter is examined. Relations between the vibrational model and the excess entropy scaling of the thermal conductivity coefficient are discussed.
Dielectric barrier discharge plasma actuators (DBDPAs) have been investigated for active flow control. The discharge induces ionic wind, which can be utilized for flow control; however, it simultaneously heats the flow and the dielectric surface. The thermal characteristics of the DBDPA must be clarified for applications in thermo-fluid engineering, such as forced convective cooling. In this study, we constructed a similarity law for the time variation of the surface temperature, assuming that the induced flow was heated by the discharge and that the dielectric was heated by the airflow. The similarity law was derived from the one-dimensional heat conduction equation in the dielectric, and the spatially averaged normalized temperature was then formulated as a function of the Biot and Fourier numbers. To experimentally validate the similarity law, the surface temperature, thrust, and power consumption were measured. The induced flow temperature and heat transfer coefficient were estimated based on the thrust and power consumption. The measured results verified that the similarity law was valid, regardless of the dielectric material, thickness, or applied voltage. This result supports the hypothesis regarding the heating mechanism in which the airflow is heated by Joule heating and the dielectric is heated by forced convection.
Ti64 alloy is a well-known material for biomedical applications due to high corrosion resistance and biocompatibility properties. Surface properties of implants plays a vital role in bone and cell growth in the human body. With the anodization process, we can increase the surface porosity, which will be adequate for surface fascination of the implant screw to the bone and appropriate mechanical properties. Hence, the present study attempted to improve the surface properties of Ti64 by anodization and plasma treatment that may be promising method to increase the biocompatibility of Ti materials. Anodization process is the cheapest one to improve the surface properties of Ti alloy and riskless process. To intensify the open pores on the Ti64 surface plasma treatment was performed. Also, the aim of this study was to improve the aesthetic appearance of the dental implants and reproduce interference of colours. With the help of UV-VIS spectrophotometer the colour and spectral reflectance were investigated. The oxide layer thickness, chemical composition and nanosurface roughness was measured. These results suggests the surface modification of Ti64 alloy by anodization can produce interference of colours and are dependent on the applied voltage, oxide layer thickness. The surface oxidation consisting of anatase and rutile phase and change in nanosurface roughness, may improve the biocompatibility of Ti64.
Forschungszentrum Jülich and partners are developing the ITER core charge exchange spectroscopy (cCXRS) hosted by upper port plug#3 (UPP). The system should withstand loading due to the plasma transients resulting in electromagnetic (EM) forces acting on the UPP and its onboard components. On the other hand, the eddy currents and shock dynamic EM loads occur in the vacuum vessel (VV) and make it vibrate. As a result, it excites the UPP and, consequently, its onboard components. The computational problem is a superposition of these solutions: 1) the deterministically calculated time-history UPP response to the applied EM forces and 2) the UPP response to the VV excitations that are specified as floor response spectra (FRS) at the port stub (attachment to the VV). On the top of this, the EM loads should be combined with the seismic ones which are also specified as an FRS. This paper considers a potential methodology for combining plasma transients with seismic events. A numerical modeling of the UPP hosting a specific cCXRS component is presented. This methodology gives a direct and transparent engineering way to estimate the mechanical strength of the UPP onboard components. The analysis uses port stub FRS input and does not depend on a spectra-to-spectra recalculation procedure (from VV to component attachment) that is well established for the seismic-type response spectra but is not validated for the FRS due to the plasma transients.
We created an ultracold plasma by photoionizing the laser-cooled and trapped rubidium atoms in a magneto-optical trap. In the externally applied direct current (DC) electric field environment, the electrons which escape from the potential well of the ultracold plasma were detected for different numbers of the ions and initial kinetic energies of the electrons. The results are in good agreement with the calculations, based on the Coulomb potential well model, indicating that the external DC field is an effective tool to adjust the depth of potential well of the plasma, and it is possible to create an ultracold plasma in a controlled manner.
A multiscale method called Equation Free Proj ective Integration (EFPI) is being applied to global gyrokinetic particle simulation of plasma turbulence, which provides a framework for studying a variety of multiscale problems in plasma physics. In our EFPI simulations, Ion-Temperature Gradient (ITG) driven transport is modeled on two scales: a microscale related to the ITG turbulence and a macroscale related to the slow-varying source term. The long timescale turbulence behavior of the system is determined by extrapolating forward in time using estimates of the macroscales obtained from short duration simulations of the microscale dynamics. In our EFPI simulations, the heat flux of the turbulence will slowly vary by way of a time varying source. We will compare directly to turbulence simulations without EFPI. The demonstration of EFPI for turbulence simulation may have impact on other multiscale problems. For example, the nonlinear interaction of different modes at different space-time scales, which is topical problem in plasma physics.