Hasil untuk "Plasma physics. Ionized gases"

Gregory K. Delipei, Quentin Faure, Maria Avramova et al.

The verification, validation, and uncertainty quantification (VVUQ) of high-fidelity, high-resolution multi-physics modeling and simulation in nuclear engineering applications are essential for assessing the predictive credibility of developed models. Appropriate practices and methods are required to address ongoing challenges. Some key examples include the large dimensionality of the input and output spaces, modeling complexity, high computational cost, scarcity of relevant experimental data, and the lack of guidelines and protocols for the development of multi-physics benchmarks. This study provides several guidelines and recommendations. Dimensionality reduction and screening approaches can be used to address the high-dimensional input and output spaces. A multi-level validation hierarchy where the coupling level is increased progressively is suggested to manage modeling complexity. A validation scoring method is proposed to compare the different coupling levels and to identify gaps in the modeling. Surrogate models can be used to address the computational cost, though they require the estimation of an additional model uncertainty. For consistent uncertainty propagation, sample-processing diagrams are introduced that can help avoid sampling errors between the multiple inputs. For the validation of multivariate outputs such as time series, local, regional, and global univariate metrics can be used together with more complicated multivariate methods based on U-pooling. Some of the proposed recommendations are demonstrated on the multi-physics modeling of the first cold ramp test from the OECD/Nuclear Energy Agency (NEA) Multi-physics Pellet Cladding Mechanical Interaction Validation (MPCMIV) benchmark. The multi-level modeling hierarchy ranges from single-physics fuel performance models to coupled multi-physics models. The MOOSE-based tools Griffin, Bison, and THM are employed alongside the fuel performance code OFFBEAT. The measurements considered in here include the cladding’s axial elongation and coolant temperature at three different locations during the cold ramp test. Validation metrics are computed at local, regional, and global scales. Validation scores are computed for each model and physics domain. The results highlight the need for at least a coupling between the RP and FP to accurately predict the cladding axial elongation, whereas the coolant temperatures are less sensitive to the coupling level due to their small variations during the cold ramp test.

Ron Grikshtas, Sergey Efimov, Nikita Asmedianov et al.

Underwater electrical explosions of single metallic wires driven by microsecond current pulses are investigated and compared with previously reported sub-microsecond experiments. Current and voltage waveforms, streak camera shadow imaging, and one-dimensional hydrodynamic simulations are employed to characterize how the energy density, energy density deposition rate, and the generated shock waves in water depend on the wire parameters. It was found that, similar to the sub-microsecond timescale, the solid–liquid phase transition occurs later than thermodynamic calculations predicted, while the liquid–vapor phase transition happens sooner than expected, leading to a two-phase coexistence. Additionally, most materials show a notable resistance peak (Ti, Fe, Ni, Zn, Ag, Sn, Ta, Au) compared to a quasi-plateau for Cu and Mo or a continuous increase for Al and Pt. Moreover, the specific action integral values are significantly smaller than those observed in wire explosion experiments in vacuum. Finally, the plasma formed at peak resistive voltage is non-ideal but exhibits lower electron density, ionization degree, and temperature compared to the sub-microsecond case.

Igor Kaganovich, Michael Tendler

Partially ionized plasma physics has attracted increased attention recently due to numerous technological applications made possible by the increased sophistication of computer modelling, the depth of the theoretical analysis, and the technological applications to a vast field of manufacturing for computer components. Partially ionized plasma is characterized by a significant presence of neutral particles in contrast to the fully ionized plasma. The theoretical analysis is based upon solutions of the kinetic Boltzmann equation, yielding the non-Maxwellian electron energy distribution function (EEDF), thereby emphasizing the difference with a fully ionized plasma. The impact of the effect on discharges in inert and molecular gases is described in detail, yielding the complex nonlinear phenomena resulting in plasma selforganization. A few examples of such phenomena are given, including the non-monotonic EEDFs in the discharge afterglow in a mixture of argon with the molecular gas NF₃; the explosive generation of cold electron populations in capacitive discharges, hysteresis of EEDF in inductively coupled plasmas. Recently, highly advanced computer codes were developed in order to address the outstanding challenges in plasma technology. These developments are briefly described in general terms.

Baimao Lei, Baimao Lei, Bohao Tian et al.

Fault detection and diagnosis (FDD) is essential for maintaining safety and preventing hazardous situations in industrial process control. Effective fault diagnosis allows for the timely detection and correction of anomalies, preventing potential disruptions and maintaining optimal performance. In the paper, we present a unified framework for fault detection and diagnosis by combining the real-time sensitivity of the moving window particle filtering (PF) with the diagnostic precision of the generalized likelihood ratio test (GLRT). Within the framework, the particle filtering is integrated to provide accurate real-time state monitoring and prediction in scenarios with nonlinear digital control system dynamics and non-Gaussian noise. The moving window (MW) is adopted to identify anomalous patterns within a stream of data by focusing on a fixed-size segment that moves across the data. The GLRT is then used to isolate the specific type of fault that has occurred based on the observed data and the different fault hypotheses and models. The method is demonstrated with a digital U-shaped tube steam generator water level control system in pressurized water reactor nuclear power plants. Comparative studies have also been conducted with LSTM network to demonstrate the effectiveness and superiority of the proposed PF-based MW-GLRT method. The demonstration results show that the proposed PF-based MW-GLRT framework can provide a robust and efficient solution for identifying and characterizing faults in complex digital control systems.

Tara Beattie, Bernd Grambow

T. von Woedtke, M. Laroussi, Matteo Gherardi

Plasma medicine refers to the application of nonequilibrium plasmas at approximately body temperature, for therapeutic purposes. Nonequilibrium plasmas are weakly ionized gases which contain charged and neutral species and electric fields, and emit radiation, particularly in the visible and ultraviolet range. Medically-relevant cold atmospheric pressure plasma (CAP) sources and devices are usually dielectric barrier discharges and nonequilibrium atmospheric pressure plasma jets. Plasma diagnostic methods and modelling approaches are used to characterize the densities and fluxes of active plasma species and their interaction with surrounding matter. In addition to the direct application of plasma onto living tissue, the treatment of liquids like water or physiological saline by a CAP source is performed in order to study specific biological activities. A basic understanding of the interaction between plasma and liquids and bio-interfaces is essential to follow biological plasma effects. Charged species, metastable species, and other atomic and molecular reactive species first produced in the main plasma ignition are transported to the discharge afterglow to finally be exposed to the biological targets. Contact with these liquid-dominated bio-interfaces generates other secondary reactive oxygen and nitrogen species (ROS, RNS). Both ROS and RNS possess strong oxidative properties and can trigger redox-related signalling pathways in cells and tissue, leading to various impacts of therapeutic relevance. Dependent on the intensity of plasma exposure, redox balance in cells can be influenced in a way that oxidative eustress leads to stimulation of cellular processes or oxidative distress leads to cell death. Currently, clinical CAP application is realized mainly in wound healing. The use of plasma in cancer treatment (i.e. plasma oncology) is a currently emerging field of research. Future perspectives and challenges in plasma medicine are mainly directed towards the control and optimization of CAP devices, to broaden and establish its medical applications, and to open up new plasma-based therapies in medicine.

Kyle G Miller, Tomas E Gutierrez, Archis S Joglekar et al.

Optical techniques for spatiotemporal control can produce laser pulses with custom amplitude, phase, or polarization structure. In nonlinear optics and plasma physics, the use of structured pulses typically follows a forward design approach, in which the efficacy of a known structure is analyzed for a particular application. Inverse approaches, in contrast, enable the discovery of new structures with the potential for superior performance. Here, an implementation of the unidirectional pulse propagation equation that supports automatic differentiation is combined with gradient-based optimization to design structured pulses with features that are advantageous for a range of nonlinear optical and plasma-based applications: (1) a longitudinally uniform intensity over an extended region, (2) a superluminal intensity peak that travels many Rayleigh ranges with constant duration, spot size, and amplitude, and (3) a laser pulse that ionizes a gas to form a uniform column of plasma. In the final case, optimizing the full spatiotemporal structure improves the performance by a factor of 15 compared to optimizing only spatial or only temporal structure, highlighting the advantage of spatiotemporal control.

Veselin Vasilev, Nikola Lazarov, Svetlana Lazarova et al.

The aim of this work is to provide an extensive experimental study of the performance of a novel magnetically and gas-flow-stabilized arc discharge for carbon dioxide (CO₂) conversion and oxygen (O₂) production on Mars. The proposed discharge provides an additional degree of freedom for easy scalability by adjusting its length. The discharge is examined at a pressure range of 200–612 mbar in order to optimize it for oxygen production on Mars, where low-pressure operation is preferable due to energy costs. Additionally, two quenching configurations with an actively cooled region are evaluated. They are compared to a benchmark configuration without additional cooling. Two high-voltage power supplies (PSs) are used, and the results are compared—a constant direct current (DC) and a pulsed unipolar current. The pulsed power supply offers better CO₂ conversion performance at lower pressure due to stable operation in an arc regime. The energy cost for oxygen production on Mars is also presented, including a conservative estimation of the energy needed for compressing the Martian atmosphere at ambient pressure to the discharge operational pressure. It is discussed how this affects the energy cost of oxygen production.

Florin Enescu, Codrina Ionita, Dan Gheorghe Dimitriu et al.

In this article, we present an overview of our investigations on the formation and behavior of space charge structures in an argon discharge plasma on gridded and smooth spherical hollow electrodes with and without orifices. Four experiments are described, in which we have used the following: (1) one spherical gridded sphere with one orifice, (2) one hollow smooth stainless steel sphere with two opposing orifices, (3) two smooth polished stainless steel spherical electrodes without orifices, (4) two smooth polished stainless steel spherical electrodes with opposing orifices. The experiments were conducted at the University of Innsbruck in a stainless steel cylindrical chamber (the former Innsbruck DP machine—IDP), and at the Alexandru Ioan Cuza University of Iaşi (Romania) in a Pyrex Vacuum Chamber (PCH). As diagnostics, we have used mainly optical emission spectroscopy to determine electron temperature and density.

Alexander C. Ervin, James D. Blakemore

The redox properties of actinide-containing species strongly influence their reactivity, speciation, and interfacial behavior, but the experimental quantification of the electrochemical characteristics of molecular actinide complexes in nonaqueous media has not received the attention it deserves. Here, results from hydrodynamic methods and electrochemical simulations of U(VI)/U(V) redox are reported, including quantification of heterogeneous electron-transfer kinetics and estimation of chemical reversibility of U(VI)/U(V) interconversion at electrodes in acetonitrile-based electrolyte. The complexes investigated are recently reported U(VI) and U(V) complexes in which the uranyl ion (UO2n+) is encapsulated in a macrocyclic 18-crown-6-like moiety templated by a Pt(II) center. These complexes feature the most positive value UVI/UV reduction potential yet reported and are thus particularly relevant to study of facile U(V) generation from U(VI) precursors as well as uranium electroanalysis. Rotating disk electrode (RDE) studies have been used to quantify the diffusion coefficients of the U(VI) and U(V) complexes, and standard heterogeneous electron transfer rate constants (k0) for the redox have been determined using a conventional Koutecký-Levich analysis. Rotating ring-disk electrode (RRDE) studies have been used to directly interrogate the chemical reversibility of U(VI)-U(V) interconversion, confirming that reduction of the U(VI) complex at an Au disk is associated with formation of the U(V) analogue that can be readily re-oxidized at a Pt ring under hydrodynamic (rotating) conditions. Because measurements of the type reported here are generally associated with current flows that are larger than those found in corresponding quiescent (unstirred) conditions, our findings suggest that hydrodynamic methods could be advantageous for design of electroanalytical approaches to detection of actinide species and study of their redox properties.

Philip Pfahl, Mustafa K. Jaradat, Mauricio E. Tano et al.

In this work, we present validation test results of fully coupled neutronics and thermal-hydraulics models of the Molten Salt Reactor Experiment (MSRE) against experimental data of the zero power pump transients and the natural circulation tests at low power. To capture the strong coupling between neutronics and thermal-hydraulics due to fuel circulation, and to account for the delayed neutron precursor (DNP) distribution, the porous media thermal-hydraulics solver Pronghorn was fully coupled to the spatial neutron dynamics code Griffin, which solves the neutron diffusion equation, and to the 0-D point kinetics solver Squirrel, using a 2-D homogenized representation of the MSRE. The validation test results show very good agreement with experimental data for both point kinetics and spatial dynamics simulations, capturing the strong feedback effect and DNP losses in the MSRE. The 0-D code Squirrel accurately predicted the time-dependent behavior in the MSRE given the steady-state spatial dynamics solution of Griffin.

Viktoriia V. Gudkova, Valentin D. Borzosekov, Maria A. Zimina et al.

This study investigates the physicochemical processes in aqueous solutions treated with a high-current (up to 300 A) pulsed multispark discharge. Pulse length was 2 μs at a 50 Hz repetition rate. The discharge occurred within bubbles of argon injected between the stainless-steel electrodes at the constant flow rate. The erosion of electrode material during the discharge led to iron and other alloy components entering the liquid. Optical emission spectra confirmed the erosion of electrode material (Fe, Cr, Ni atoms and ions). EDTA and its disodium salt were used in order to study their effect on the metal particle formation process. Treatment with deionized water led to an increase in conductivity and the generation of hydrogen peroxide (up to 1200 µM). In contrast, the presence of EDTA and its disodium salt drastically altered the reaction pathways: the H₂O₂ yield decreased, and the solution conductivity dropped substantially for the acidic form of EDTA, while the decrease was minor for EDTA-Na₂. This effect is attributed to the buffered chelation of eroded metal ions, forming stable Fe-EDTA complexes, as confirmed by a characteristic absorption band at 260 nm. The results demonstrate the critical role of complex-forming agents in modulating plasma–liquid interactions, shifting the process from direct erosion products to the formation of stable coordination compounds.

Stefan Finsterle, Matthew Waples, Mengzhu Yang et al.

The performance of a deep borehole repository for the disposal of radioactive waste may be affected by the generation of hydrogen gas produced by the corrosion of the steel canisters and the borehole casing. In particular, the evolution of a free gas phase may lead to high overpressures within the borehole and near field of the repository, displacing radionuclides dissolved in pore water, and facilitating the transport of volatile radionuclides. These processes are analyzed by numerical modeling of non-isothermal, multiphase flow and transport of hydrogen gas and water in a generic deep horizontal borehole repository completed in an argillaceous host rock. The near-field submodel addresses gas generation within and outside the canister and the effect of canister breach on near-field pressure and saturation distributions; a repository-scale model examines the effect of gas generation in a long disposal section. The models support canister and design decisions for deep borehole repositories. The simulations reveal the significance of the repository design on gas flow, both on the local scale of the components of the engineered barrier system, and on the larger scale of the repository layout. It can be concluded that for a typical design of a deep horizontal borehole repository, corrosion gases are contained within the disposal section of the borehole, or effectively dissipate into the repository’s near field without generating excessive overpressures that affect the integrity of the engineered barrier system or the overall performance of the repository.

Jean-Christophe Pain

We present analytical estimates for the maximum line strength in a transition array, as well as for the numbers of strong and weak lines. For that purpose, two main assumptions are used as concerns the line strength distribution. The first one, due to Porter and Thomas, is more suitable for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>J</mi><mo>−</mo><msup><mi>J</mi><mo>′</mo></msup></mrow></semantics></math></inline-formula> sets, where <i>J</i> is the total atomic angular momentum, and the second one, based on a decreasing-exponential modeling of the line-amplitude distribution, is more relevant for an entire transition array. We also review the different approximations of overlapping and blanketing (band model), insisting on the computation and properties of the Elsasser function. We compare different approximations of the Ladenburg–Reiche function giving the equivalent width of an ensemble of lines in a frequency bin and discuss the possibility of using statistical indicators, such as the Chernoff bound or the Gini coefficient (initially introduced in economics for the measurement of income inequality), in the statistical characterization of transition arrays.

S. Zhao, B. Huang, C. Zhang et al.

Runaway electrons are a fundamental aspect of the physics behind gas discharge driven by nanosecond voltage pulses.[1] Investigating the runaway electron energy distribution and its formation mechanism is a key focus of both plasma application and plasma physics.[2] Recently, under the scheme of ionization waves, a groundbreaking method has been developed to reconstruct the runaway electron energy distribution function (EEDF) using X-ray spectrum.[3] This innovative approach offers new insights into the behavior of runaway electrons.

J. Freundlich

The interstellar medium of galaxies is composed of multiple phases, including molecular, atomic, and ionized gas, as well as dust. Stars are formed within this medium from cold molecular gas clouds, which collapse due to their gravitational attraction. Throughout their life, stars emit strong radiation fields and stellar winds, and they can also explode as supernovae at the end of their life. These processes contribute to stirring the turbulent interstellar medium and regulate star formation by heating up, ionizing, and expelling part of the gas. However, star formation does not proceed uniformly throughout the history of the Universe and decrease by an order of magnitude in the last ten billion years. To understand this winding-down of star formation and assess possible variations in the efficiency of star formation, it is crucial to probe the molecular gas reservoirs from which stars are formed. In this article following my presentation at the 10th International Conference on Frontiers of Plasma Physics and Technology held in Kathmandu from 13-17 March 2023, I review some aspects of the multiphase interstellar medium and star formation, with an emphasis on the interplay between neutral and ionized phases, and present recent and ongoing observations of the molecular gas content in typical star-forming galaxies across cosmic time and in different environments. I also present some of our understanding of star-forming galaxies from theoretical models and simulations.

Bo Wang, Zhitao Xu, Lianjie Wang et al.

To address the efficiency bottleneck encountered in reactor design calculations for the newly developed lead-based reactor neutronics analysis code system MOSASAUR, we recently developed acceleration functions based on various coarse-mesh finite difference (CMFD) methods and spatial domain decomposition parallel algorithm. However, the applicability of these improvements to different lead-based reactors remains to be analyzed. This work collected and established core models for various types of lead-based reactor. Based on different SN nodal transport solvers, we analyzed the acceleration performance of different CMFD methods, different CPU cores, and the combination of CMFD and parallel calculation. The results indicated that the impact of different CMFD acceleration or parallel acceleration on the calculation accuracy was negligible; the rCMFD method had good stability and convergence rate, achieving speedup of several to dozens; parallel efficiency was related to the number of meshes, and for large reactor cores, superlinear speedup was achieved with 200 CPU cores; rCMFD and parallel computing could achieve combined speedup, with 200 cores achieving speedup of hundreds to thousands, typically completing a reactor core transport calculation in 1 min.

Jessica Blenkinsop, Aditya Rivonkar, Mathurin Robin et al.

Oxalic acid is encountered within industrial processes, spanning from the nuclear sector to various chemical applications. The persistence and potential environmental risks associated with this compound underscore the need for effective management strategies. This article presents an overview of different approaches for the destruction of oxalic acid. The study explores an array of degradation methodologies and delves into the mechanistic insights of these techniques. Significant attention is channeled towards the nuclear industry, wherein oxalic acid arises as a byproduct of decontamination and waste management activities. An integral aspect of decommissioning efforts involves addressing this secondary waste-form of oxalic acid. This becomes imperative due to the potential release of oxalic acid into waste streams, where its accommodation is problematic, and its capacity to solubilize and transport heavy metals like Pu is a concern. To address this, a two-tiered classification is introduced: high concentration and low concentration scenarios. The study investigates various parameters, including the addition of nitric acid or hydrogen peroxide, in the presence of metallic ions, notably Mn2+ and Fe2+. These metallic ions are common components of effluents from metallic waste treatment. Additionally, the impact of UV light on degradation is explored. Investigations reveal that at high concentrations and with the influence of hydrogen peroxide, the presence of metallic cations accelerates the rate of destruction, demonstrating a direct correlation. This acceleration is further enhanced by exposure to UV light. At low concentrations, similar effects of metallic cations are observed upon heating the solution to 80°C. The rate of destruction increases proportionally with hydrogen peroxide concentration, with an optimal oxalic acid to hydrogen peroxide ratio of 1:100. Interestingly, a low-power UV light exerted no discernible effects on the destruction rate; heating alone proved sufficient. In essence, regardless of concentration, the degradation of oxalic acid with hydrogen peroxide experiences acceleration in the presence of metallic ions such as Mn2+ and Fe2+.

Devanshi Bhardwaj, Bin Cheng, David J. Sprouster et al.

With significant improvement in High Temperature Superconductors (HTS), several projects are adopting HTS technology for fusion power systems. Compact HTS tokamaks offer potential advantages including lower plant costs, enhanced plasma control, and ultimately lower cost of electricity. However, as compact reactors have a reduced radial build to accommodate shielding, HTS degradation due to radiation damage or heating is a significant and potentially design limiting issue. Shielding must mitigate threats to the superconducting coils: neutron cascade damage, heat deposition and potentially organic insulator damage due x-rays. Unfortunately, there are currently no hi-performance shielding materials to enable the potential performance enhancement offered by HTS. In this work, we present a manufacturing method to fabricate a new class of composite shields that are high performance, high operating temperature, and simultaneously neutron absorbing and neutron moderating. The composite design consists of an entrained metal-hydride phase within a radiation stable MgO ceramic host matrix. We discuss the fabrication, characterization, and thermophysical performance data for a series of down-selected composite materials inspired by future fusion core designs and their operational performance metrics. To our knowledge these materials represent the first ceramic composite shield materials containing significant metal hydrides.

Seda Yilmaz, Paul K. Romano, Lorenzo Chierici et al.

In this study, we present a detailed comparison of two independently developed models of the Molten Salt Reactor Experiment (MSRE) for Monte Carlo particle transport simulations: the constructive solid geometry (CSG) model that was developed in support of the MSRE benchmark in the International Handbook of Evaluated Reactor Physics Benchmark Experiments, and a CAD model that was developed by Copenhagen Atomics. The original Serpent reference CSG model was first converted to OpenMC’s input format so that it could be systematically compared to the CAD model, which was already available as an OpenMC model, using the same Monte Carlo code. Results from simulations using the Serpent and OpenMC CSG models showed that keff agreed within 10 pcm while the flux distribution in space and energy generally agreed within 0.1%. Larger differences were observed between the OpenMC CAD and CSG models; notably, the keff computed for the CAD model was 1.00872, which is more than 1% lower than the value for the CSG model and much closer to experiment. Several areas of the reactor that were modeled differently in the CSG and CAD models were discussed and, in several cases, their impact on keff was quantified. Lastly, we compared the computational performance and memory usage between the CAD and CSG models. Simulation of the CSG model was found to be 1.4–2.3× faster than simulation of the CAD model based on the Embree ray tracer while using 4× less memory, highlighting the need for continued improvements in the CAD-based particle transport ecosystem. Finally, major performance degradation was observed for CAD-based simulations when using the MOAB ray tracer.