Hasil untuk "Plasma physics. Ionized gases"

Hasupama Jayasinghe, Liliana Arevalo, Richard Morrow et al.

Implementing a computationally efficient numerical model for a single streamer discharge is essential to understand the complex processes such as lightning initiation and electrical discharges in high voltage systems. In this paper, we present a streamer discharge simulation in air, by solving one-dimensional (1D) drift diffusion reaction (DDR) equations for charged species with the disc approximation for electric field. A recently developed fourth-order space and time-centered implicit finite difference method (FDM) with a flux-corrected transport (FCT) method is applied to solve the DDR equations, followed by a comparative simulation using the well-established explicit FDM with FCT. The results demonstrate good agreement between implicit and explicit FDMs, verifying their reliability for streamer modeling. The total electrons, total charge, streamer position, and hence the streamer bridging time obtained using the FDMs with FCT agree with the same streamer computed in the literature using different numerical methods and dimensions. The electric field is obtained with good accuracy due to the inclusion of image charges representing the electrodes in the disc method. This accuracy can be further improved by introducing more image charges. Both implicit and explicit FDMs effectively capture the key streamer behavior, including the variations in charged particle densities and electric field. However, the implicit FDM is computationally more efficient.

Emory Colvin, Todd S. Palmer

Sandia National Laboratories’ Annular Core Research Reactor (ACRR) is a unique research reactor, using UO2-BeO fuel and operating primarily in pulsed mode. To better understand the physical characteristics of the fuel, the distribution of heat generation must be understood. Previous work developed a Serpent two model of the ACRR and Python coupling script to provide multiphysics feedback. Simulations of $1.50 and $2.00 pulses were compared to experimental results. This paper expands this work to $2.50 and $3.00 pulses. It further explores potential improvements to the model: dividing the fuel into two radial regions for feedback purposes, allowing additional iterations of the multiphysics coupling and checking for convergence, and the development of alternate specific heat capacity values. The use of two radial fuel regions improved agreement with experimental results for the simulations using the original function for specific heat capacity as a function of temperature but did not consistently improve results with the constant value for specific heat capacity. Allowing additional multiphysics iterations until the power distribution field converges also produced little change for reactor power prediction, though it improved maximum fuel temperature prediction slightly. The new values for specific heat capacity provided the most significant improvements to the models. A third-order polynomial developed from experimental data results in a significant improvement in fuel temperature prediction over the constant value with only a small loss of performance in reactor power prediction.

Nadia Imtiaz, Saeed Ur Rehman, Liu Chao et al.

We present three dimensional particle-in-cell simulations of current-voltage characteristics of the hemispherical Langmuir probe (LAP), onboard the China Seismo-Electromagnetic Satellite (CSES). Using realistic plasma parameters and background magnetic fields obtained from the International Reference Ionosphere (IRI) and International Geomagnetic Reference Field (IGRF) models, we simulate probe–plasma interactions at three locations: the equatorial region and two magnetically conjugate mid-latitude sites: Millstone Hill (Northern Hemisphere) and Rothera (Southern Hemisphere). The simulations, performed using the PTetra PIC code, incorporate realistic LAP geometry and spacecraft motion in the ionospheric plasma. Simulated current voltage characteristics or I–V curves are compared against in-situ LAP measurements from CSES Orbit-026610, with Pearson’s correlation coefficients used to assess agreement. Our findings indicate how plasma temperature, density, and magnetization affect sheath structure and probe floating potential. The study highlights the significance of kinetic modeling in enhancing diagnostic accuracy, particularly in variable sheath regimes where classic analytical models such as the Orbital-Motion-Limited (OML) theory may be inadequate.

Keiichiro Takeda, Naoki Sato

We present the noncanonical Hamiltonian structure of the relativistic Euler equations for a perfect fluid in Minkowski spacetime. By identifying the system’s noncanonical Poisson bracket and Hamiltonian, we show that relativistic fluid flows preserve helicity and enstrophy as conserved quantities in three-dimensional and two-dimensional cases, respectively. This holds when the fluid follows a relativistic γ-barotropic equation of state, which generalizes the classical barotropic condition. Furthermore, we demonstrate that these conserved quantities are Casimir invariants associated with the noncanonical Poisson structure. These findings open new avenues for applying Hamiltonian theory to the study of astrophysical fluids and relativistic plasmas.

Blake Haist, Richard E. Wirz

Network analysis is a convenient method for analyzing cold atmospheric plasma (CAP) devices across a wide range of operating conditions. By using frequency and voltage as nodes in the network, edges are formed between nodes when the combination of voltage and frequency results in an ignited plasma jet. Singular value decomposition is used to identify modalities in the network that are representative of operational modes in the plasma jet. An analysis of the spectra produced by the jet provides validation of the operational modes and shows that voltage and frequency predominately affect the operation of the jet with remarkable independence.

Xinliang Xu, Yihang Chen, Yulin Zhou et al.

The mechanisms by which rotation influences zonal flows (ZFs) in plasma are incompletely understood, presenting a significant challenge in the study of plasma dynamics. This research addresses this gap by investigating the role of non-inertial effects—specifically centrifugal and Coriolis forces—on Geodesic Acoustic Modes (GAMs) and ZFs in rotating tokamak plasmas. While previous studies have linked centrifugal convection to plasma toroidal rotation, they often overlook the Coriolis effects or inconsistently incorporate non-inertial terms into magneto-hydrodynamic (MHD) equations. In this work, we derive self-consistent drift-ordered two-fluid equations from the collisional Vlasov equation in a non-inertial frame, and we modify the Hermes cold ion code to simulate the impact of rotation on GAMs and ZFs. Our simulations reveal that toroidal rotation enhances ZF amplitude and GAM frequency, with Coriolis convection playing a critical role in GAM propagation and the global structure of ZFs. Analysis of simulation outcomes indicates that centrifugal drift drives parallel velocity growth, while Coriolis drift facilitates radial propagation of GAMs. This work may provide valuable insights into momentum transport and flow shear dynamics in tokamaks, with implications for turbulence suppression and confinement optimization.

Martin Navarro

Site selection procedures for deep geological repositories are driven by the rejection of candidate sites whose degree of long-term protection is insufficient or less sufficient. If long-term protection is defined in relation to future exposures, it has to be operationalized, that is, translated into measurable indicators, such as dose or degree of containment, which, again, have to be evaluated by safety assessments. Site selection procedures, therefore, depend on the quality with which long-term protection is operationalized and assessed. Although it is widely acknowledged that operationalizations and assessments of long-term protection are inherently inaccurate, little attention has been paid to the question whether these inaccuracies prevent site selection procedures from improving long-term protection. Still, there is no theory of site selection that could specify the conditions under which site selection procedures are rational with regard to the target of long-term protection. To contribute to such a theory, a conceptual model is presented that explores how site rejection decisions can be justified by inaccurate operationalizations and safety assessments. The model rests on the assumption that site rejections are justified by logical arguments. By explicating what is needed to support the arguments, the model displays the complex structure of the justification, which, amongst others, rests on the quality of operationalization, safety assessment and system understanding. The presented argument-based approach is novel in the context of site selection. However, it is not meant as an alternative to multi-criteria decision-making, but as a necessary complement to understand the potential and limitations of safety-related decision criteria. The presented model identifies which types of errors are tolerable in the context of site selection and it explains why error tolerance is lowest for safety comparisons. The model points out that the frequently used assessment strategy of conservatism is not suitable for rejecting sites for reasons of insufficient or lower safety. It also shows that consensual requirements for the conditions under which long-term protection is achieved may be powerful tools for site selection.

Mark D. DeHart, Emily Shemon, Deokjung Lee

Harshini Mohan, Subash Mohandoss, Natarajan Balasubramaniyan et al.

Non-thermal plasma (NTP)-assisted material synthesis and surface modification provide a promising approach in various applications, particularly in wastewater treatment. In this study, we reported the synthesis of photocatalytic zinc oxide (ZnO) from zinc hydroxide (Zn(OH)₂) utilizing NTP discharge generated by dielectric barrier discharge (DBD). The results demonstrated that the 40 min plasma treatment at 200 °C (ZnO-P) with a voltage of 20 kV significantly improved the material’s physicochemical properties compared to conventional calcination at 600 °C (ZnO-600). ZnO-P exhibited better crystallinity, a significantly reduced particle size of 41 nm, and a narrower band gap of 3.1 eV compared to ZnO-600. Photocatalytic performance was evaluated through crystal violet degradation, where ZnO-P achieved an 60% degradation rate after 90 min of UV exposure, whereas ZnO-600 exhibited only a 50% degradation rate under identical conditions. These findings underscore the effectiveness of NTP synthesis in enhancing the surface properties of ZnO, leading to superior photocatalytic performance.

F.T.T. Houng, S.Y. Hoh, J.F. Ong

We show that the wakefield driven by fast electrons inside the nanowire when irradiated with an ultra-short relativistic laser pulse strips atoms to a higher charge state. Using particle-in-cell simulations, we demonstrate that the charge state agrees with the barrier suppression threshold of the wakefield and reaches a higher value via collision. The ionisation of gold nanowires occurs only via collisional-damped wakefield. We found that the collisional ionisation of high-Z nanowires depends on the onset of the z pinch. These results suggest a different ionisation mechanism of the structured target in the subfemtosecond regime.

B. Grambow, B. Grambow, R. Müller et al.

Understanding of the properties of dissolution and precipitation of Uranium under reducing geochemical conditions is important in radioactive waste management and assessments of natural uranium deposits. The mechanism of forming UO2+y from U(VI) and U(IV) containing aqueous solution (1 M NaCl) and the solubilities of the precipitates were studied under well-controlled reducing conditions as a function of pH, particle size, and supersaturation. The results show that tetramer and colloid formation are critical initial steps. Precipitation is not growth-controlled but appears to be nucleation-controlled, with critical nuclei dimensions of one unit cell of UO2. The precipitates were always crystalline, and amorphous UO2 was not observed.

B. Coppi

Helical plasma structures have been identified and shown to form in and propagate from the high density plasmas in which Black Hole binaries can be imbedded. These structures are envisioned to extend to very low density and distant plasma regions up to where they can be disrupted by encountering plasma patches where the waves, of which the structures are composed, become dissipated. By now experimental observations and analyses of the morphology of jets have found that they can involve double-helix magnetic topologies in one case and, more recently, a single helix in other cases. Thus, plasma structures originating in the plasmas surrounding binary systems are proposed, instead of particle beams emitted by black holes directly, as a possible explanation of the origin of the highly collimated jets associated with a variety of celestial objects that are currently observed. Theoretically, double-helix structures are found to emerge as non-linearly coupled torsional ion-sound waves which, in the presence of a background magnetic field, in both the formation and terminal plasmas generate helical magnetic field configurations while remaining nearly “electrostatic” in regions where no significant background magnetic field is present. These (helical) structures can propagate independently in either of the two vertical directions. The coupling involves Intrinsic Gravitational Modes originating in the circumbinary disk and Inner Gravitational Fluctuations emerging from the Swept (Toroidal) Regions carved, within the highest density plasma region, by one or both Black Holes.

David García, Romain V. H. Dagnelie, Mavrik Zavarin

Jan Weiland, Tariq Rafiq, Eugenio Schuster

Turbulence and transport phenomena play a crucial role in the confinement and stability of tokamak plasmas. Turbulent fluctuations in certain physical quantities, such as density or temperature fluctuations, can have a wide range of spatial scales, and understanding their correlation length is important for predicting and controlling the behavior of the plasma. The correlation length in the radial direction is identified as the critical length in real space. The dynamics in real space are of significant interest because transport in configuration space is primarily focused on them. When investigating transport caused by the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi mathvariant="bold">E</mi><mo>×</mo><mi mathvariant="bold">B</mi></mrow></semantics></math></inline-formula> drift, the correlation length in real space represents the size of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi mathvariant="bold">E</mi><mo>×</mo><mi mathvariant="bold">B</mi></mrow></semantics></math></inline-formula> whirls. It was numerically discovered that in drift wave turbulence, this length is inversely proportional to the normalized mode number of the fastest growing mode relative to the drift frequency. Considerable time was required before a proper analytical derivation of this condition was accomplished. Therefore, a connection has been established between phenomena occurring in real space and those occurring in k-space. Although accompanied by a turbulent spectrum in k-space with a substantial width, transport in real space is uniquely determined by the correlation length, allowing for accurate transport calculations through the dynamics of a single mode. Naturally, the dynamics are subject to nonlinear effects, with resonance broadening in frequency being the most significant nonlinear effect. Thus, mode number space is once again involved. Resonance broadening leads to the detuning of waves from particles, permitting a fluid treatment. It should be emphasized that the consideration here involves the total electric field, including the induction part, which becomes particularly important at higher beta plasmas.

J.T. Mendonça

We consider the linear and nonlinear properties of twisted plasmons propagating in a magnetized plasma. Twisted plasmons are electron plasma waves with a finite amount of angular momentum. In contrast with plane plasma waves, which propagate along the static magnetic field direction with the same dispersion as in isotropic plasmas, the properties of twisted waves depend on the value of their angular momentum. A new dispersion relation is derived, using the fluid approximation. We also study nonlinear effects associated with twisted plasmons, and show that they introduce electromagnetic corrections. Of particular relevance is the excitation of a quasi-static magnetic field, which is associated with finite amplitude plasmon solutions.

Bernardo Magaldi, Júlia Karnopp, Argemiro da Silva Sobrinho et al.

This work reports on the (zero-dimensional) global model study of argon plasma chemistry for a cylindrical thruster based on inductively coupled plasma (ICP) whose output has a system of two grids polarized with each other with direct current potential. The global model developed is based on particle and energy balance equations, where the latter considers both charged and neutral species. Thus, the model allows the determination of the neutral gas temperature. Finally, this study also investigated the role of excited species in plasma chemistry especially in the ions production and its implications for propulsion parameters, such as thrust. For this, the study was carried out in two different scenarios: (1) one taking into account the metastable species Ar^r and Ar^p (multi-step ionization), and (2) the other without these species (single-step ionization). Results indicates a distinct behavior of electron temperature with radiofrequency (RF) power for the investigated cases. On the other hand, the gas temperature is almost the same for investigated power range of up to 900 W. Concern propulsion analysis, a thrust of 40 mN at 450 W was verified for case (1), which represents a remarkable thrust value for electric thrusters.

Matías G. Ferreyra, Brenda L. Fina, Natalio J. Milardovich et al.

In recent years, one of the fastest growing technological applications in the field of nonthermal plasmas is the degradation of organic contaminants of water. In this work, the degradation of indigo carmine (IC) in water induced by a pulsed positive corona discharge operating in ambient air is reported. Degradation levels in different volumes of IC in solution with distilled water treated with different plasma exposure times immediately after discharge (0 h), and in the postdischarge up to 24 h were examined. To explain the IC discoloration in the postdischarge phase, a chemical model was developed. The stability of the reactive species in solution nitrate (NO₃⁻), nitrite (NO₂⁻) and hydrogen peroxide (H₂O₂), as well as the properties of the solution (electrical conductivity, pH) were also measured. The results suggest that the hydroxyl radical (OH˙) as well as ozone (O₃) are the main oxidizing species during the discharge phase, being primarily formed in the gas phase through plasma-mediated reactions and then transferred to the liquid by diffusion, while the OH˙ production in the bulk liquid through the decomposition of peroxinitrous acid (O=NOOH) plays a major role in the IC degradation during the postdischarge. These results are associated with a noticeably increase in the energy-yield values observed at 24 h post-treatment.

Matthew Mieles, Callie Stitt, Hai-Feng Ji

The chemical treatment of wood has been shown to increase its mechanical strength by forming composites with a variety of polymers. Polyethylene glycol diacrylate (PEGDA) has commonly been used as a polymer reinforcement to increase the strength and resistance of spruce wood for various applications, such as protection from weathering. In this study, PEGDA was impregnated into wood samples and polymerized by dielectric barrier discharge (DBD) plasma to form wood–polymer composites (WPCs). The kinetic rate order of PEGDA was explored using FT-IR quantitative analysis and the DBD plasma-initiated polymerization was determined to be second order. The strength of the wood samples was then determined by a three-point flexural test. The PEGDA-treated spruce wood samples showed improved flexural strength versus the untreated wood samples. The WPCs were also made using a UV treatment method and were then compared to the DBD plasma-treated samples. The results showed that the DBD plasma-treated samples yielded superior flexural strength relative to the UV-treated samples. We accredited this difference in strength to the plasma process and its ability to penetrate into the various layers of the wood and initiate polymerization, as opposed to UV light that can only penetrate superficially, initiating polymerization in only the first few layers of the wood surface.

Marina Kühn-Kauffeldt, Marvin Kühn, Michael Mallon et al.

In-orbit additive manufacturing (AM) is a promising approach for fabrication of large structures. It allows to expand and accelerate human space exploration possibilities. Extrusion-based AM was demonstrated in zero gravity, while the realization of such a process in orbit-like vacuum conditions is currently under exploration. Still, a solution for protection of the UV and IR radiation sensitive polymers is needed in order to prevent their early mechanical failure under space conditions. Vacuum arc plasma based process is widely applied on earth for thin protective coating deposition. Its major advantage is its scalability—from tiny size used in electric propulsion to large scale coating devices. The usability of the vacuum arc process in space conditions was shown in electric propulsion applications in nano-satellites. In this work we discuss and demonstrate the integration of vacuum arc process as a post processing step after Fused Filament Fabrication (FFF) for additive manufacturing and functionalization of long polymer structures. Here we address the concept for technical realization, which integrates the vacuum arc into additive manufacturing process chain. More over we present a laboratory prototype, which implements this concept together with a use case, where a previously printed PEEK structure is coated with aluminum based coating suitable for UV radiation protection.

Ting Liu, Igor Timoshkin, Mark P. Wilson et al.

The present paper investigates the breakdown characteristics—breakdown voltage, with breakdown occurring on the rising edge of the applied HV impulses, and time to breakdown—for gases of significance that are present in the atmosphere: air, N₂ and CO₂. These breakdown characteristics have been obtained in a 100 µm gap between an HV needle and plane ground electrode, when stressed with sub-µs impulses of both polarities, with a rise time up to ~50 ns. The scaling relationships between the reduced breakdown field <i>E_tip</i>/<i>N</i> and the product of the gas number density and inter-electrode gap, <i>Nd</i>, were obtained for all tested gases over a wide range of <i>Nd</i> values, from ~10²⁰ m⁻² to ~10²⁵ m⁻². The breakdown field-time to breakdown characteristics obtained at different gas pressures are presented as scaling relationships of <i>E_tip</i>/<i>N</i>, <i>Nd</i>, and <i>Nt_br</i> for each gas, and compared with data from the literature.