Hasil untuk "Plasma physics. Ionized gases"

Anbang Sun, Yulin Guo, Yanru Li et al.

Filamentary mode, as a common phenomenon that appears in dielectric barrier discharge (DBD), is realized by rod-to-rod electrodes in N₂-O₂ mixtures at 80 mbar. The effects of the dielectric thickness on the characteristics of filamentary DBD are investigated through experiments and simulations. The discharges are driven by a positive unipolar nanosecond pulse voltage with 15.8 kV amplitude, 9 ns rise time (<i>T</i>_r^10–90%), and 14 ns pulse width. The characteristics of filamentary DBD are recorded with an intensified charge-coupled device and a Pearson current probe in the experiment, and a 2D axisymmetric fluid mode is established to analyze the discharge. Surface discharges occur on the anode and cathode dielectric after the breakdown, and the discharge is gradually extinguished as the applied voltage decreases. A thinner total dielectric thickness (<i>D</i>_a + <i>D</i>_c) leads to larger currents, stronger discharges, and wider discharge channels. These characteristics are consistent when the total dielectric thickness is the same but anode dielectric thickness and cathode dielectric thickness are different (<i>D</i>_a ≠ <i>D</i>_c ≠ 0). If the anode is a metal electrode (<i>D</i>_a = 0), the current will be substantially large, and two discharge modes are observed: stable mono-filament discharge mode and random multi-filament discharge mode. It is found in simulations that the dielectric thickness changes the electric field configuration. The electric field is stronger with the decrease in dielectric thickness and leads to a more intense ionization which is responsible for most of the observed effects.

Ramin Ghahri Shirinabadi, Feng Zhu, Mangaljit Singh et al.

We investigate the underexplored multiphoton ionization regime of resonantly enhanced harmonic generation in gallium laser-ablation plumes. Resonant harmonics generate quasi-monochromatic extreme ultraviolet radiation with a pronounced coherent intensity enhancement. In this experimental study, we systematically examine high-order harmonic generation yield by independently varying the energies of the pre-pulse, which forms the laser-ablation plume, and the main pulse, which drives the harmonic emission. This approach enables precise evaluation of how each pulse contributes to the overall efficiency of resonant harmonic generation. Throughout this study, we identify the optimal conditions for maximizing the generation efficiency of gallium resonant harmonics driven by a 400 nm laser. Our results demonstrate an effective method for generating intense, quasi-monochromatic femtosecond extreme ultraviolet radiation and offer valuable insight into the role of autoionizing resonances within the multiphoton ionization regime.

A. S. Joglekar, A. G. R. Thomas

Vlasov-Poisson-Fokker-Planck (VPFP) simulations of large-amplitude electron plasma waves, where the bounce frequency is much larger than the collision frequency, $ω_B \gg ν_\text{ee}$, show that the evolution of these waves exhibits three phases; I. A short-lived trapping phase during which collisional effects are minimal. II. A long-lived detrapping phase during which collisional effects are most influential. III. A short-lived Landau damping phase where the effect of collisions becomes minimal again. While the dispersion relation during the trapping and Landau damping phase is well known, the wave behavior during the detrapping phase is not as well understood. The simulations show that during the detrapping phase, the interplay between weak electron-electron collisions and strong wave-electron interactions results in an increasing frequency shift further from the linear root, $ω_\text{EPW}$. At the conclusion of the detrapping phase, the distribution function is nearly Maxwellian, the frequency shift rapidly diminishes, and the wave damps at a larger rate than the Landau damping rate. Empirical fits to the damping rates, frequency shift enhancement rate, and the lifetime of the plasma waves are provided as functions of collision frequency, wavenumber, and wave amplitude.

S. L. Siddanathi, L. Westerberg, H. Åkerstedt et al.

In a non-transferred plasma torch, the working gas becomes ionized and forms plasma as it interacts with the electric arc at the cathode tip. However, in certain cathode shapes, particularly flat ones, and under specific conditions, the gas flow can separate at the cathode tip, forming a vortex region. While this flow separation is influenced by geometric factors, it occurs in the critical zone where plasma is generated. Understanding the causes of this separation is essential, as it may significantly impact torch performance. If the separation proves detrimental, it is important to identify ways to mitigate it. This paper presents a computational analysis of a non-transferred plasma torch to investigate the physics behind flow separation. The results highlight the location and causes of the separation, as well as its potential advantages and disadvantages. Finally, the paper explores theoretical approaches to address flow separation in plasma torches, offering practical insights for enhancing their design and efficiency.

Kimberly J. Chan, A. Stancampiano, K. Skinner et al.

Cold atmospheric plasmas (CAPs) have emerged as the central component to plasma medicine, a relatively new research field in which CAPs have shown promise for a variety of biomedical uses and medical therapies. CAPs comprise of a partially ionized gas that exists at near room temperature and atmospheric pressure. CAPs affect biological materials via chemical, thermal, and electrical interactions that are observable using common plasma characterization measurements. For cases in which the to-be-characterized interface is already exposed (e.g., early skin cancer detection), we propose CAPs can be used for real-time tissue identification in a noninvasive manner. We leverage the sensitivity of CAP interactions with biological interfaces to identify and differentiate biological tissues by using real-time chemical (via optical emission spectra) and electrical (via voltage probes along the circuit) measurements. These information-rich measurements have embedded physics knowledge about the plasma chemistry and its interactions with biological tissues. Thus, we incorporate common physics knowledge to extract and analyze such measurements using machine learning. Our proof-of-concept studies demonstrate that biological tissues can be differentiated with up to 99% test accuracy when differentiating four tissue types (i.e., skin, muscle, bone, and fat) of an ex vivo chicken model. The proposed CAP tissue identification and differentiation approach can effectively augment the medical diagnostic toolkit, including in cancer detection, vascular studies, and real-time surgical analysis.

Marcel Ebeling, Martina Heiermann, Klaus-Jürgen Röhlig

In the TRANSENS research project (2019–2025), large-scale transdisciplinary research on nuclear waste management is being conducted for the first time in Germany. Transdisciplinary in this context means that non-specialists and practice actors are systematically involved in developing and addressing research questions. One out of four TRANSENS research topics is addressing optimization potential for the Safety Case (SC) for Deep Geological Repositories (DGR) for nuclear waste. Seven workshops on this topic were held with three working groups, which differed from one another in terms of their types of knowledge. The work focused on the area of FEP (features, events, and processes) and scenarios. It also shows how objections and optimization proposals for safety cases differ between the various transdisciplinary working groups. Accessibility of SC content was identified as a fundamental area for improvement. Summaries of the report that are appropriate for various target audiences were called for, as was the inclusion of experts from outside the established SC community. The use of digital presentations and communication options was examined in detail. Regarding FEP processing, matrix forms of representation were discussed which, in addition to representing general dependencies, can also depict the strength of these dependencies. There were also proposals for the use of a morphological box to achieve this goal and to be able to create scenarios from FEP. Suggestions were made as to when FEP should be excluded from catalogs, when scenarios can be discarded and how these processes could be documented. To find previously unknown FEP, ideas were put forward regarding a reward system through which the general public could contribute to the completeness of the FEP catalog. In all workshops, promising and valuable results (e.g., criticisms, ideas) were achieved through transdisciplinary research. In TRANSENS, it was proven that the participation of non-experts in research can lead to substantive and in-depth suggestions for improvement. This also means that meaningful contributions based on participatory research are possible in broad participatory processes such as the German site selection procedure. It remains to be seen to what extent the results obtained in TRANSENS will be considered in the preparation of the future German Safety Cases.

Davide Pettinari, Samuele Meschini , Raffaella Testoni 

The development of fusion energy systems demands structural components capable of withstanding extreme operational conditions, including intense neutron fluxes, high thermal and mechanical loads, and stringent requirements on neutron activation. Several structural materials have been proposed, such as nickel-based superalloys, reduced activation ferritic/martensitic steels, oxide-dispersion-strengthened alloys, SiC/SiC ceramic matrix composites, and vanadium-based alloys. While those materials have been extensively analysed for large tokamaks, no comparative studies exist on compact tokamaks. This work addresses this gap by considering an ARC-class tokamak as representative of compact design. The materials are evaluated based on the following criteria: power density deposition, absorption rate, TBR, energy multiplication factor within the breeding blanket, and displacement per atom. Numerical simulations were performed using the OpenMC Monte Carlo particle transport code to evaluate the neutronic behavior and activation characteristics of the selected structural materials. A simplified compact reactor model was developed using Constructive Solid Geometry (CSG) to enable consistent and reproducible comparisons. ODS steels and vanadium-based alloys emerged as the most promising candidates for application in compact, high-temperature fusion devices. ODS steels combine low activation with favorable performance across all evaluated metrics, offering a balanced tritium breeding capability alongside good resistance to radiation damage. Vanadium-based alloys, in turn, exhibit very low hydrogen and helium production, minimal power density deposition, facilitating heat removal from the structural material, and activation levels significantly lower than those of conventional austenitic steels. Across all materials, the simulations predict TBR values in the range of 0.90–1.25, energy multiplication factors of between 1.12 and 1.18, and first structural layer power densities of over 7 MW/m3. In the most favourable cases, the shutdown dose rates fall below natural background levels in less than 50 years.

Weihua Jiang

This review article is the continuation of a previous publication, by the same author, on one dimensional theory of space charge effect and virtual cathode. The virtual cathode is known to be unstable. However, the process of virtual cathode oscillation is very complicated both physically and mathematically. No satisfactory theoretical model exists that can fully describe the oscillatory behavior of the virtual cathode. On the other hand, computer simulations allow us to numerically observe this phenomenon and establish certain relations between the electron beam parameters and the virtual cathode characteristics. This article explains the detailed procedure of numerical modeling by dealing with the one-dimensional case as an example. A sample code written in the C language is attached at the end following the main text. This article is expected to serve as a reference for young researchers and students who are interested in computer simulations of intense particle beams and high-power microwave generation.

K. Hara, Anubhav Dwivedi

Spacecraft electric propulsion plays a critical role in in-space missions. Understanding the state of the ionized gas, i.e., plasmas, is important for the characterization of thruster performance and the lifetime. In this talk, we present the recent development of data assimilation (DA) framework that estimates state variables and parameters obtained from a physics-based dynamical model with noisy experimental data. We have developed DA techniques based on variants of Kalman filters to estimate state and parameters in plasma systems governed by coupled nonlinear ordinary and partial differential equations.

Shireen Mahala Tagore, Syed Muzammil Tahamul, Shaik Aathif et al.

Often regarded as the fourth state of matter, the term ‘plasma’ is important for sophisticated technologies including space propulsion and industrial cutting. During the course of the project, we created a simple plasma gun prototype to exhibit how plasma may be produced and manipulated via the laws of physics. The design includes two electrodes with an inert gas like argon flowing in between them and is connected to a high-voltage power supply. An electric arc creates ionization in the gas which gives out a stream of plasma while its exit is controlled by magnetic coils which demonstrate an electromagnetic effect on the plasma as charged particles. This setup is based on core principles like electric discharge, Joule heating, Lorentz force, and basic fluid dynamics. While quite simple, our model attempts to demonstrate the core principles of electric discharge, Joule heating, and the Lorentz force. It allows capturing first-hand experience with effects that tend to be relegated to textbooks or labs. Other versions of the system are in use for an array of applications such as plasma cutters, ion thrusters, and even as sterilizers. The target for this project is to lower the barriers for students and educators while encouraging innovation around plasma technology for future projects.

LI Jingze, ZHAO Mingliang, ZHANG Yuru et al.

Capacitively coupled plasma sources, which are widely used in the etching and deposition processes of semiconductor manufacturing, have the advantages of simple structure, low cost, and the ability to generate large-area uniform plasma. To meet the requirements of advanced processes, fluid models are usually required to simulate plasma sources and optimize their important plasma parameters, such as density and uniformity. In this paper, an independently-developed capacitive coupled plasma fast simulation program is employed to conduct three-dimensional fluid simulations of a dual-frequency capacitive coupled Ar/CF4 plasma source, with the aims of verifying the effectiveness of the program and investigating the influence of discharge parameters such as gas pressure, high and low-frequency voltages, low-frequency frequency, and background component ratios. The simulation results show that the program has an extremely high simulation speed. As the low-frequency voltage increases, plasma density initially remains approximately constant and then significantly increases, while plasma uniformity initially rises and then significantly decreases, the γ-mode heating of low-frequency source increases in this process, and becomes the dominant mode in replace of the α -mode of high-frequency source. As the lower frequency increases, plasma density initially remains approximately constant and then slightly increases, while plasma uniformity changes little, these are because the γ -mode heating is frequency independent, while the α -mode heating is much lower than that of high-frequency source. As the high-frequency voltage increases, plasma density significantly increases, while plasma uniformity initially rises and then significantly decreases, the α -mode heating of highfrequency source is significantly enhanced in this process. As the pressure increases, plasma density significantly increases, and plasma uniformity also rises significantly, the reason is the more complete collision between particles and background gases. As the Ar ratio in background gases increases, plasma density changes slightly, the densities of Ar-related particles generally increase and the densities of CF4-related particles generally decrease, although there are some non-monotonic changes in particle densities, which reflects the mutual promotion between some ionization and dissociation reactions.

J. Boeuf

The formation of self-organized luminous structures or striations in the positive column of rare gases is linked to the development of ionization waves. In this study, we examine a neon plasma column at low current, under conditions where metastable ionization is negligible. Recently, a Particle-In-Cell Monte Carlo Collisions method successfully simulated plasma instabilities in a rare gas positive column, realistically reproducing the formation of striations. To elucidate the mechanisms responsible for stratification, a fluid model was linearized around the uniform state of a positive column. The linear analysis revealed a positive growth rate, indicating instability, when the density gradient coefficient in the electron energy flux (thermoelectric transport coefficient or Dufour density gradient coefficient) was negative, a common characteristic in rare gases. The validity of the fluid approach in the conditions of stratification is, however, questionable. In the present paper, we use a kinetic approach, based on Monte Carlo simulations in the presence of a given perturbation of the electric field, to investigate the mechanisms leading to stratification. Our findings confirm that while the fluid model fails to capture the intricate physics of stratification, the kinetic approach underscores the crucial role of the thermoelectric transport coefficient in the emergence of striations in rare gases. Additionally, our results corroborate previous studies that identified resonances in the electron response to the perturbation. However, unlike earlier work, we find that these resonances produce minima rather than maxima in the growth rate and are not responsible for stratification.

Juan Long, Tiejun Wang, Fukang Yin et al.

The evolution of the THz waveform generated from the two-color air filament was experimentally investigated by moving an iris along the plasma channel. By taking the differentiation of the measured THz waveforms, the local longitudinally resolved THz waves along a 54 mm-long filament were obtained. The local THz pulse underwent periodic phase shifts. A theoretical deduction indicates that the phase shifts are mainly caused by the dispersion in the plasma channel which plays a dominant role in the evolution of the local THz waveforms.

Svetlana Lazarova, Tsvetelina Paunska, Veselin Vasilev et al.

This work investigates <i>CO</i>₂ conversion using atmospheric pressure low-current gliding discharges (GD). The following three modifications are studied: classic GD; magnetically accelerated GD (MAGD); and magnetically retarded GD (MRGD). In the latter two, permanent magnets produce a magnetic field that either accelerates or retards the discharge downstream. The gas flow is confined between quartz plates and the electrodes, with varying channel thicknesses. The magnetic configurations improve the performance compared to the classic GD, with up to 30% higher energy efficiency and up to a 50% higher conversion rate. The highest conversion rate is 11–12% with 10% energy efficiency, while the highest efficiency is 40% with 5% conversion, achieved with MRGD and MAGD at channel thicknesses of 2 mm and 3 mm.

Tomas Bensadon, Mervi J. Mantsinen, Thomas Jonsson et al.

The PION code has been integrated into the European Transport Solver (ETS) transport workflow, and we present the first application to model Ion Cyclotron Resonance Frequency (ICRF) heating scenarios in the next-step fusion reactor ITER. We present results of predictive, self-consistent and time-dependent simulations where the resonant ion concentration is varied to study its effects on the performance, with a special emphasis on the resulting bulk ion heating and thermal ion temperature. We focus on two ICRF heating schemes, i.e., fundamental H minority heating in a ⁴He plasma at 2.65 T/7.5 MA and a three-ion ICRF scheme consisting of fundamental ³He heating in a H-⁴He plasma at 3.3 T/ 8.8 MA. The H minority heating scenario is found to result in strong absorption by resonant H ions as compared to competing absorption mechanisms and dominant background electron heating for H concentrations up to 10%. The highest H absorption of ∼80% of the applied ICRF power and highest ion temperature of ∼15 keV are obtained with an H concentration of 10%. For the three-ion scheme in 85%:15% H:⁴He plasma, PION+ETS predicts ³He absorption in the range of 21–65% for ³He concentrations in the range of 0.01–0.20%, with the highest ³He absorption at a ³He concentration of 0.20%.

Joanna McFarlane

Advanced reactor technologies are being considered for the next-generation of nuclear power plants. These plants are designed to have a smaller footprint, run more efficiently at higher temperatures, have the flexibility to meet specific power or heating needs, and have lower construction costs. This paper offers a perspective on molten salt reactors, promoted as having a flexible fuel cycle and close-to-ambient pressure operation. A complexity introduced by reducing the reactor footprint is that it may require low-enriched fuel for efficient operation, available from enrichment of the feed salt or by reusing actinides from existing used nuclear fuel (UNF). Recycling UNF has the potential to reduce high-level waste, if done correctly. Release limits from UNF processing are stringent, and processes for waste reduction, fission gas trapping, and stable waste-form generation are not yet ready for commercial deployment. These complex processes are expensive to develop and troubleshoot because the feed is highly radioactive. Thus, fuel production and supply chain development must keep abreast of reactor technology development. Another aspect of reactor sustainability is the non-fuel waste streams that will be generated during operation and decommissioning. Some molten salt reactor designs are projected to have much shorter operational lifetimes than light-water reactors: less than a decade. A goal of the reactor sustainability effort is to divert these materials from a high-level waste repository. However, processing of reactor components should only be undertaken if it reduces waste. Economic and environmental aspects of sustainability are also important, but are not included in this perspective.

Jian Deng, Jianjun Xiao, Songbai Cheng et al.

Anna Markhotok

This work is an addition to the previously developed two-dimensional model of the shock–plasma interaction, extending it into the third dimension. The model can trace the evolution of the state of the hypersonic flow and the shock front refracted at a thermal discontinuity. The advantages of using the spherical coordinate system for this type of problem include increased transparency in interpreting the solution and a shortened calculation procedure, because all the changes to the front are reduced to one distortion component. Although the vorticity generation triggered at the interface is a consequence of the refraction and tied to the steep changes in the front, it is shown here that this is not because of an instant parameter jump at the interface due to refraction itself.

Jean-Christophe Pain

Spectral line shapes are a key ingredient of hot-plasma opacity calculations. Since resorting to elaborate line-shape models remains prohibitive for intensive opacity calculations involving ions in different excitation states, with <i>L</i>, <i>M</i>, etc., shells are populated, and Voigt profiles often represent a reliable alternative. The corresponding profiles result from the convolution of a Gaussian function (for Doppler and sometimes ionic Stark broadening) and a Lorentzian function, for radiative decay (sometimes referred to as “natural” width) and electron-impact broadening. However, their far-wing behavior is incorrect, which can lead to an overestimation of the opacity. The main goal of the present work was to determine the energy (or frequency) at which the Lorentz wings of a Voigt profile intersect with the underlying Gaussian part of the profile. It turns out that such an energy cut-off, which provides us information about the dominant line-broadening process in a given energy range, can be expressed in terms of the Lambert <i>W</i> function, which finds many applications in physics. We also review a number of representations of the Voigt profile, with an emphasis on the pseudo-Voigt decomposition, which lends itself particularly well to cut-off determination.