Hasil untuk "Plasma physics. Ionized gases"

Xinpei Lu, G. Naidis, M. Laroussi et al.

Ovidiu S. Stoican

A novel system aiming to electrically supply various cold plasma generators is proposed. It operates as a programmable linear current source which is able to maintain a dc constant discharge current at various discharge voltages required to sustain the plasma jet. Its design is based on a specific electronic device called a switchable current regulator, which considerably simplifies the circuit topology. Experimental results carried out in real operating conditions confirm the practical purpose of the proposed solution.

J. Riba, Milad Soltany, Adrián Cabello

Paschen’s law describes the breakdown voltage of a gas as a function of gap distance and gas pressure. This fundamental principle of high-voltage physics and engineering significantly impacts the operation, design, and safety of various electrical and plasma-based technologies, including air ionizers, aircraft, and satellites. Originally developed for uniform electric fields, such as those between two parallel plates or spheres, Paschen’s law determines the voltage required to initiate an electric arc. It predicts that the breakdown voltage is a unique function of the pressure-distance product p·d, with a minimum value occurring at a specific p·d. This work proposes a practical laboratory session or guided project for physics or engineering courses to determine Paschen’s law based on laboratory measurements for non-uniform electrode geometries under a 50 Hz sinusoidal supply. A rod-plane gap geometry produces a highly non-uniform electric field distribution, enabling corona discharges to occur before complete breakdown of the air gap. The experimental results presented here indicate that partial discharges tend to occur at higher p·d values for a rod-plane geometry than predicted by Paschen’s law. However, the results approach Paschen’s values as the p·d product decreases. Additionally, the results show that corona discharges occur well before complete air gap breakdown at high p·d values, and that each pressure has a unique curve relating breakdown voltage to the p·d product. Therefore, the results deviate from original Paschen’s law. This paper analyzes the concepts of partial discharges and complete breakdown and discusses the conditions leading to one or the other. The discharges were detected by remotely controlling a smartphone camera via open-source software. A complete dataset is provided that can be used directly for developing practical or guided projects. Students also have the option of acquiring their own data using the simple experimental setup outlined in this paper.

J. Gwak, Min-Gu Yoo, Hee Taek Kim et al.

This work presents a model for predicting electron energy gain from electron cyclotron (EC) wave–particle interactions during the breakdown phase of tokamak pre-ionization. Investigation of this phase to infer the EC requirements inevitably demands high-fidelity simulation study covering gas breakdown physics, plasma dynamics, and EC absorption. Under the significantly low density and temperature, electrons interact nonlinearly with EC wave and gain energy of which picture is distinct from the linear or quasilinear EC heating. For room temperature electrons, analytic estimates of energy gain have been derived using adiabatic nonlinear theory (Farina 2018 Nucl. Fusion 58 066012). However, electrons with large incident perpendicular energy can be generated from the ionization reactions and even be present in the Maxwellian tail during the breakdown. In this work, we refined the theory into a semi-analytic form that predicts nonlinear energy gain of arbitrary perpendicular energy. The semi-analytic model is demonstrated to be accurate and efficient in calculating macroscopic electron energy absorption: the expected total absorbed energies agree well with the numerical counterparts for key characteristic electron distributions, and computation time is significantly reduced by several orders of magnitude. This work is envisaged to offer a practical tool for electron avalanche dynamics study, contributing to development of predictive capability on EC pre-ionization phase of future tokamaks such as ITER and K-DEMO.

A. Mazzeo, F. Laggner, K. J. Ammons et al.

Abstract The Large, Uniform Plasma for Ionizing Neutrals (LUPIN) is a radio-frequency (RF) inductively coupled plasma (ICP) chamber for demonstrating plasma performance of an RF ICP positive ion source upgrade for the DIII-D neutral beam injection (NBI) system. LUPIN will be used to investigate ion source physics, including neutral gas dynamics, plasma density uniformity, interactions with Faraday shields, and power coupling to novel RF antenna designs. LUPIN has an RF generator capable of delivering 20 kW of power at 2 MHz, which is coupled into a cylindrical quartz vessel measuring 20 cm in length and 10 cm in radius. This configuration matches the power density requirements for a full-scale ion source. Target hydrogen and deuterium plasma densities exceeding 1018 m-3 would relate to extracted ion current densities of 2100 A/m2 for 10s. Vacuum conductance and gas flow calculations predict a maximum achievable neutral gas flow rate of 1675 Pa $ \cdot $⋅ L/s at 5 Pa of He, which mimics the gas flow of the DIII-D NBI system. Designs have been developed for an internal Faraday shield to mitigate heat flux and ion sputtering on the dielectric vessel. Thermomechanical finite element simulations demonstrated the Faraday shield design to be capable of withstanding anticipated heat loads from worst-case operation scenarios. Results of upcoming experimental investigations on LUPIN will guide the design of a full-scale prototype for DIII-D integration.

Nicola Pedroni

The Critical Heat Flux (CHF) is a physical phenomenon that may cause the deterioration of the heat transfer in the core of nuclear reactors, potentially leading to core damage. Its accurate prediction is therefore a crucial issue in nuclear reactor safety. To this aim, various empirical and mechanistic models have been proposed to estimate the CHF across various flow regimes and conditions, which however present some drawbacks: i) data scarcity in some parts of the input domain; ii) no information about prediction uncertainties; iii) difficult explainability and interpretability of the results. To address these issues, ensembles of Physics-Enhanced Neural Networks (PENNs) are considered to predict the CHF as a function of relevant physical input variables (e.g., pipe heated length and diameter, pressure, mass flux, outlet quality). Two different frameworks to integrate physics and data-driven NN-based strategies are here compared for the first time, to the best of the author’s knowledge. In the first, fixed-structure (prior) baseline models (i.e., the Groeneveld Look-Up Table-LUT and the mechanistic Liu model) are constructed relying on the existing knowledge on the physical phenomenon of interest, which serves as a reference solution; then, NN ensembles are employed to capture unknown, unexplored information from the mismatch (i.e., the residuals) between the real CHF values and the estimates produced by the knowledge-based models. In the second, the LUT and the mechanistic Liu model are directly implemented in the NN loss function for effective (physics- and data-driven) ensemble training. A case study is carried out with an extensive CHF database (published by the U.S. Nuclear Regulatory Commission with measurements in vertical uniformly-heated water-cooled cylindrical tubes) to demonstrate: i) the improved performance of the PENN-based approaches as compared to traditional knowledge-based models; ii) the PENN superior generalization capabilities over standalone data-driven NNs in the presence of small-sized datasets (i.e., a few tens or hundreds points); iii) the possibility to build robustness in the CHF predictions by bootstrap and PENN weights random reinitialization for quantifying uncertainty and estimating prediction intervals.

Aleksey Chaplygin, Mikhail Yakimov, Sergey Vasil’evskii et al.

This paper investigates a novel combined laser and plasma heating test technique. Integrating the 1.5 kW Raycus RFL-C1500 laser source into the VGU-4 Inductively Coupled Plasma Facility (IPMech RAS) allowed the study of fine-grain MPG-7 graphite ablation in the high-temperature range from 2920 to 3865 K under exposure to subsonic nitrogen plasma flow and combined exposure to nitrogen plasma flow and laser irradiation. Graphite nitridation and sublimation were observed. The subsonic nitrogen plasma flow was characterized by numerical modeling, probes, and spectral measurements. The proposed experimental approach is promising for simulating the entry conditions of planetary mission vehicles into different atmospheres.

Manish Kumar, Manish Kumar, Manish Joshi et al.

The study of the transport and deposition characteristics of aerosol particles in test sections is a component of the probabilistic safety assessment of nuclear reactors under severe accident scenarios. The deposited particles may become resuspended under favorable conditions, thus affecting the source term estimates. The objective of the present study was to perform experiments on a straight test pipe section 4 m long under deposition and resuspension phases. Zinc oxide metal particles generated from a plasma torch aerosol generator (PTAG) were used as the test aerosols. Deposition phase experiments were performed at a total carrier gas flow rate of 180 Lmin-1, whereas the flow was increased to 1265 Lmin-1 for the resuspension phase. Thermophoresis as an effect of PTAG enthalpy-governed temperature gradients was seen to dominate the deposition phase. The effects of varying Reynold numbers in different volume sections were reflected in a higher resuspended-to-deposited-mass-ratio in the downstream direction. A profile of deposited and resuspended masses was interpreted for the resuspension time of 20 min. Experimentally obtained characteristics were also compared with numerical results from simulations performed with the SOPHAEROS module of the Accidental Source Term Evaluation Code (ASTEC). This study, performed at the National Aerosol Facility (NAF), Indian Institute of Technology, Kanpur, India, indicates the need of more research on aerosol resuspension effects as this impacts the estimation accuracy of the source term.

J. E. Mastache-Mastache, M. C. González, H. Martínez et al.

This computational study investigates the optical properties of a sixth-order Fibonacci quasi-periodic photonic crystal cavity designed for the infiltration of near-infrared colloidal quantum dots (QDs, e.g., InAs/ZnSe or PbS) and fully compatible with plasma-enhanced chemical vapor deposition (PECVD) using porous silicon layers. Using the transfer matrix method (TMM), we simulate transmission (T), reflection, absorption, electric field distributions and Purcell factors (F) for both TE and TM polarizations, incorporating the wavelength-dependent absorption of porous silicon. A multi-objective figure-of-merit is defined to simultaneously maximize transmission (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>T</mi><mo>></mo><mn>95</mn><mo>%</mo></mrow></semantics></math></inline-formula> at 800 nm) and the one-dimensional Purcell factor. The optimized structure (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>P</mi><mi>H</mi></msub><mo>=</mo><mn>0416</mn></mrow></semantics></math></inline-formula>) yields a quality factor <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>Q</mi><mo>≈</mo><mn>4300</mn></mrow></semantics></math></inline-formula>, a 1D Purcell factor <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>F</mi><mrow><mn>1</mn><mi>D</mi></mrow></msub><mo>≈</mo><mn>3.6</mn></mrow></semantics></math></inline-formula> and a realistic 3D Purcell enhancement estimated between 4 and 8 (under lateral confinement assumptions). This conservative estimate, derived via the effective index method to account for 3D effects, aligns with the detailed discussion within the article and is lower than the ideal upper bound of the 1D model. The integrated emission enhancement is approximately 3.0-fold. Monte Carlo simulations demonstrate remarkable robustness to fabrication tolerances (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>±</mo><mn>10</mn></mrow></semantics></math></inline-formula> nm thickness variations result in a <5% reduction in transmission), highlighting the structure’s scalability for PECVD-based processing. Comparison with periodic Bragg structures reveals superior angular stability and disorder tolerance in the Fibonacci design, positioning it as a promising platform for robust QD-based light sources and integrated refractive index sensors.

Giovanni Lapenta, Jean Berchem, Mostafa El-Alaoui et al.

We present a method to visualize and analyze turbulence within macroscopic flows that feature complex structures not determined by the turbulence itself. We introduce a technique to shift to a Lagrangian frame that captures the macroscopic scales not part of the turbulent cascade. We then study turbulence within this frame that is comoving with the large-scale nonturbulent flow. The method is applied to Particle-in-Cell simulations of astrophysical plasma. Specifically, we use two cases to illustrate the new method. First, we consider a magnetic perturbation in the solar wind interacting with the bow shock, magnetosheath, and magnetopause in the dayside of the Earth. Second, we consider an Earthward flow generated by magnetic reconnection in the magnetotail. In these cases we show how the Lagrangian frame can be used to distinguish turbulent fluctuations from the macroscopic flow structures due to the evolution of the system caused by macroscopic forcing.

O.V. Kosulya, B. M. Romaniuk, O.S. Oberemok et al.

The Institute of Applied Physics of the National Academy of Sciences of Ukraine has developed a design of a highly efficient ion source for ion implantation with Penning system cold cathode. Ionization of a solid-phase substance occurs due to interaction with fast oscillating electrons in a longitudinal magnetic field. A beam of ions of the plasma-forming gas and the sprayed solid-phase substance is extracted through a cylindrical hole of the emission cathode with a diameter of 1.6…1.9 mm. The ion source was tested on the BALZERS MPB-202 ion implanter at the V. E. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine.

E. M. Silich, E. Bellomi, J. Sayers et al.

Galaxy cluster mergers are representative of a wide range of physics, making them an excellent probe of the properties of dark matter and the ionized plasma of the intracluster medium. To date, most studies have focused on mergers occurring in the plane of the sky, where morphological features can be readily identified. To allow study of mergers with arbitrary orientation, we have assembled multi-probe data for the eight-cluster ICM-SHOX sample sensitive to both morphology and line of sight velocity. The first ICM-SHOX paper [1] provided an overview of our methodology applied to one member of the sample, MACS J0018.5+1626, in order to constrain its merger geometry. That work resulted in an exciting new discovery of a velocity space decoupling of its gas and dark matter distributions. In this work, we describe the availability and quality of multi-probe data for the full ICM-SHOX galaxy cluster sample. These datasets will form the observational basis of an upcoming full ICM-SHOX galaxy cluster sample analysis.

T. Johnson, L.-G. Eriksson

This paper presents a new Monte Carlo algorithm intended for use in orbit following Monte Carlo codes (OFMC) to describe resonant interaction of ions with Radio Frequency (RF) waves in axi-symmetric toroidal plasmas. The algorithm is based on a quasi-linear description of the wave–particle interaction and its effect on the distribution function of a resonating ion species. The algorithm outlined in the present paper utilises a two-step approach for the evaluation of the Monte Carlo operator that has better efficiency and a stronger convergence than the standard Euler–Maruyama scheme. The algorithm preserves the reciprocity of the diffusion process. Furthermore, it simplifies how the displacement of the resonance position, as a result of wave–particle interaction, is accounted for. Such displacements can have a noticeable effect on the deterministic part of the Monte Carlo operator. The fundamental nature of guiding centre displacements of resonant ions as a result of wave–particle interaction is reviewed.

Leonid Burakovsky, Scott D. Ramsey, Roy S. Baty

As UO2 is easily oxidized during the nuclear fuel cycle it is important to have a detailed understanding of the structures and properties of the oxidation products. Experimental work over the years has revealed many stable uranium oxides including UO2, U4O9 (UO2.25), U3O7 (UO2.33), U2O5 (UO2.5), U3O8 (UO2.67), and UO3, all with a number of different polymorphs. These oxides are broadly split into two categories, fluorite-based structures with stoichiometries in the range of UO2 to UO2.5 and less dense layered-type structures with stoichiometries in the range of UO2.5 to UO3. While UO2 is well characterized, both experimentally and computationally, there is a paucity of data concerning higher stoichiometry oxides in the literature. In this work we determine the ambient melting points of all the six stoichiometric uranium oxides listed above and compare them to the available experimental and/or theoretical data. We demonstrate that a family of the six ambient melting points map out a solid-liquid transition boundary consistent with the high-temperature portion of the phase diagram of uranium-oxygen system suggested by Babelot et al.

Peng Wang, Mukesh Bachhav

Jonathan 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.

A. Wright, D. D. Hartog, B. Geiger et al.

Stellarators, together with tokamaks, represent the two mainstream approaches to realizing fusion energy via toroidal magnetic confinement of highly ionized gases - plasmas - at extremely high temperatures. Improving our understanding of how macroscopic flows impact equilibrium and dynamics in stellarators closes a significant knowledge gap and is necessary to advance the physics basis of stellarators as a fusion pilot plant (FPP) concept. This is especially critical for the US stellarator design program, in both the public and private sectors, where stellarator FPP concepts are based almost exclusively on leveraging quasisymmetries. With this submission we invite the community to consider how the need for improving physics understanding of flows in advanced stellarators can serve as a catalyst for diagnostic and measurement innovation. This includes the identification of synergies with on-going technology development activities as well as opportunities to leverage new and emerging capabilities that may stem from hardware improvements and software, for example, application of AI/ML and workflow integration and management.

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Melanie Pannach, Iris Paschke, Volker Metz et al.

Sorel phases are the binder phases of the magnesia building material (Sorel cement/concrete) and of special concern for the construction of long-term stable geotechnical barriers in repositories for radioactive waste in rock salt, as potentially occurring brines are expected to contain MgCl2. Sorel phases, in addition to Mg(OH)2, are equally important as pH buffers to minimize solubility and potential mobilization of radionuclides in brine systems. In order to obtain a detailed database of the relevant solid-liquid equilibria and the related pHm values of the equilibrium solutions, extensive experimental investigations were carried out. Solid phase formation was studied by suspending MgO and Mg(OH)2 in NaCl saturated MgCl2-solutions at 25°C. Mg(OH)2 and the 3-1-8 Sorel phase were identified as the stable solid phases, while the 5-1-8 Sorel phase is metastable. Equilibration at 40°C did not lead to any solid phase changes. Both OH− and H+ equilibrium concentrations were analyzed as a function of MgCl2 concentration at 25°C and 40°C. In addition to our already published solid-liquid equilibria for the ternary system Mg-Cl-OH-H2O (25°C–120°C), the equilibrium H+ concentrations (pHm) determined at 25°C, 40°C and 60°C are now reported. Analyzing these data together with known ion-interaction Pitzer coefficients, the solubility constants for Mg(OH)2 and the 3-1-8 phase at these three temperatures, for the metastable 5-1-8 phase at 25°C and for the 2-1-4 phase at 60°C have been consistently calculated.

Ghadi Dakroub, Thomas Duguet, Corinne Lacaze-Dufaure et al.

Plasma polymerized (PP) thin films deposited in a soft or intermediate plasma discharge from hexamethyldisiloxane (HMDSO) were developed as sensors for the detection of volatile organic compound (VOC) vapors. Energy dispersive X-ray spectroscopy (EDX) and X-ray reflectometry (XRR) were performed to determine the organosilicon films’ elemental composition and density. Spectroscopic ellipsometry measurements were carried out to determine the refractive index of the films. Quartz crystal microbalance (QCM) and ellipsometry coupled to vapor sorption were used to investigate the sorption mechanism of several VOC vapors into the films as a function of the plasma deposition conditions. The density and the refractive index of the PP-HMDSO films increased with the plasma energy due to a different chemical composition and different proportion of free volumes in the material network. The PP-HMDSO films showed different affinities towards the VOC vapors depending on the plasma discharge energy. The films elaborated in the lowest plasma energy revealed a good sensitivity towards the VOCs, especially toluene (one of the BTEX vapors), compared to the other films deposited under higher plasma energy. In addition, the selectivity between toluene and other non-BTEX VOCs such as heptane and ethanol decreased to become zero while increasing the plasma energy.