The transition dynamics from the capacitive to inductive (E-H) coupling in a 2.45 GHz excited inductively coupled plasma (ICP) source is investigated using a set of microwave time resolved records at different frequencies [1]. This method, applied for the first time in the semiconductor physics [2] and for measurements of time resolved cyclotron resonances [3], has been newly adapted for plasma investigations. A number of gases like argon, helium, nitrogen, and oxygen plasmas have been analyzed in the range 20 - 1000 Pa with a constant excitation power in the range of 20-40 W. With a better resolution than $1 \mu$ s one can identify, depending on pressure, the coexistence of the E and H modes, a hybrid EH mode, and in case of oxygen plasma, the transition from negative to positive ions. The E-H transition time increases with pressure. The identification of the E or H modes become possible by analyzing the time evolution of n the resonances in power - frequency diagrams and Smith diagrams. The method requires a resonant structure (always available for microwave excitation) and a vector network analyzer (VNA) capable to meaure in pulsed regime the complex scattering parameterS11. Because of jitter the optical triggering of the VNA is not sufficient for precise determining the ignition time. An additional mathematical procedure has been implemented to precisely detect the ignition time and to make a reliable average of several recorded transients. The time evolution of plasma density is comparable with steady state measurements made at different absorbed powers [4] and described theoretically by global model [5].
When a high voltage is applied, the increase of the current and electron temperature cause many cathode spots to appear on the cathode. The plasma between the electrodes is produced by multiple cathode spots on the surface of the cathode, with plasma jets produced by each cathode spot mixing between the electrodes to form a plasma arc column. Therefore, an in-depth study of the mixing mechanism and behavior of vacuum arc jets produced by multiple cathode spots under high current is crucial for achieving a better understanding of vacuum arc theory. In this study, based on a three-dimensional steady Magneto-Hydro-Dynamic (MHD) model, employs computational fluid dynamics software Fluent to investigate and analyze mixing mechanism of multi-cathode spot jets. The objective of this study is to gain insight into the impact of various parameters such as currents, contact gap distance and axial magnetic field (AMF), on the mixing mechanism and behavior of vacuum arc jets. The characteristics distribution of ion density, ion temperature and ion pressure were given and analyzed. These results can not only contribute to the enrichment of vacuum interrupter theory, but also provide a theoretical basis for the further improvement and advancement of vacuum interrupter.
Interleukin-6 (IL-6) is a critical inflammatory factor, that plays an important role in the inflammatory process and immune system by binding with IL-6 receptor. Cold atmospheric plasma (CAP) has been proven to be efficient in lowering the expression of IL-6 in inflammatory reactions by experiments. However, it remains unclear whether the CAP-induced electric field will affect the protein conformation and function of IL-6. The molecular dynamics method is applied to reveal the electric field dependence of IL-6 in conformation change. We found that when the electric field frequency is higher than 30 MHz, the electric field period is too short to divert the total dipole moment, and can only change the unstable N terminal structure of IL-6. However, when the frequency is lower than 30 MHz, the polarization of IL-6 increases, resulting in the fracture of disulfide bonds between long helices and the reduction of IL-6 stability. As for another factor of electric field intensity, the conformation change of IL-6 becomes more and more drastic with the electric field intensity increasing, while the conformation changes little when the electric field intensity is lower than $0.5 \mathrm{~V} / \mathrm{nm}$. The final protein docking results showed that the CAPinduced electric field prevents some important docking residues of IL-6 and its receptor from binding under the conditions of 30 MHz frequency and $0.5 \mathrm{~V} / \mathrm{nm}$ intensity. This work suggests that the appropriate frequency and intensity of the electric field can affect the binding ability of IL-6 to its receptor to a certain extent, which can provide certain theoretical guidance for the parameter selection of CAP treatment related diseases.
Understanding the rapid dynamics of the primary streamer is crucial for comprehending the nanosecond pulsed discharge process. To reveal the fast primary streamer process, this study introduces a newly developed quadruple emICCD camera system capable of capturing a sequence of four discharge images in single pulse, coupled with self-customized software for data analysis. A nanosecond pulse power with its FWHM of 10.5 ns was applied to a coaxial reactor, focusing on the dynamics of the primary streamer. Our research clarifies the spatiotemporal variations of the primary streamer’s properties and examines their relation with inner electrode diameter (i.d. 0.2–2.0 mm). Results showed that in a pulse-powered coaxial electrode, there are three stages in the primary streamer process and that i.d. serves as an important factor influencing the formation and propagation of streamers. Interestingly, we found that streamer head velocity, streamer width, and streamer area for individual streamers remain constant prior to streamer channels reaching the outer electrode. Furthermore, we also observed an initial increase followed by a decrease in both streamer head velocity and streamer width with increasing i.d values. This study sheds light on the fundamental properties of the primary streamer during nanosecond pulsed discharge, contributing valuable insights for future plasma applications.
Hydrophobic materials in geotechnical engineering and soil science can have natural or artificial origin. They can be applied, e. g., to waterproof structures in the industry. In this contribution, hydrophobic granular material was manufactured through a cold plasma polymer coating procedure. The monomer used was C4F8 (octafluorocyclobutane) and the material to be coated was Hamburg sand, a coarse grained sand. In this context, computed microtomography and environmental scanning electron microscopy were used to investigate the materials in their unsaturated state. The tools are applied to visualize unsaturated phenomena on the microscale. The hydrophobic and untreated materials were imaged by both techniques at different saturation degrees in order to understand the influence of the coating on the sample’s hydraulic behaviour. The chosen environmental scanning electron microscope is able to provide relative humidity in the sample chamber, and so water drops were condensed on the grain surface, allowing to also observe the initial contact of water and the hydrophobic coating. It was observed how the capillary menisci, their geometry and contact properties evolve at different degrees of saturation. The measurements obtained and respective analyses state qualitatively the influence of the hydrophobic coatings on the pore water dynamics at different saturation degrees, which dictates the material’s hydraulic behaviour. Contact angles were also analysed were it was physically possible.
Understanding of key physics and engineering parameters is one of the most important issues to conduct fundamental design studies of future fusion reactors. Also, sensitivity analyses of performance by parameter surveys need to be done for optimizing a reactor. This research aims at a qualitative analysis to identify directions of design parameter optimization for fusion reactors. For this purpose, a Core-SOL-Divertor (CSD) model has been employed, because it is suitable for a wide range of parameter surveys by changing various parameters with low computational costs. This paper analyzes the particle and energy balances of the JT-60U divertor plasma by using a CSD model and reveals dependencies of the balances on design parameters of the device. In addition, the same CSD model is applied to conduct divertor plasma analyses for a future demonstration reactor (JA-DEMO). The result shows that it is possible to obtain a low temperature state of its divertor plasma as has been already reported by a two-dimensional SOL-Divertor integrated code. From these results, this paper shows that the CSD model is applicable to basic studies of directions and design concepts for future fusion reactors.
Nonlinear partial differential equations (NPDEs) in applied science provide an appropriate platform for the creation of novel research in the disciplines of applied mathematics and physical sciences. The development of more effective computer and simulation approaches for analysing these equations is extremely important. Researchers can roughly correctly identify themselves from the process described by solving these equations, enabling them to learn about some realities that are difficult to understand by regular observation. Mathematical and computational modelling have aided in the understanding of real-world phenomena observed in quantum mechanics, optical fiber communications, mechanical engineering, plasma physics, fluid mechanics, etc. A stochastic process is an observation at a specific time that results in a random variable. Brownian motion is a stochastic process that is both a martingale and a Markov process. We expect that recent breakthroughs in stochastic calculus via stochastic partial differential equations (SPDEs) will establish the framework for thoroughly modeling real-world models. Mathematicians, more than anybody else, are most at ease applying SPDEs and stochastic processes to natural models. We will investigate the impact of different stochastic types on the behaviour of the offered solutions. Random effects were found to modify the intensity of the energy wave or the collapse produced by model medium turbulence. Using Matlab software, various profile pictures are given to describe the behaviour of the dynamics for the offered solutions.
CFETR, also known as the China Fusion Engineering Test Reactor, is a significant undertaking planned by the Chinese government. This project serves as a bridge between ITER and DEMO, based on the experience from Experimental Advanced Superconducting Tokamak and ITER. The magnet system of CFETR consists of 16 toroidal field (TF) coils, eight central solenoid coils, and seven poloidal field coils. The dimensions of the TF coil of CFETR are 21.7 m in height and 12.3 m in width, which makes it a big challenge in manufacturing. During operation, various disruptions may occur, leading to instability in the conductors. To ensure sufficient stability against these disruptions, the CFETR TF coil has been meticulously designed. The TF magnets operate at a current of 95,600 A/turn to generate a 6.5 T field at the plasma centre. The peak magnetic field on the coil reaches 14.43 T, and the maximum stress exceeds 700 MPa. The winding package (WP) of CFETR TF coil was winded by cable-in-conduit conductor and graded into three sub-WPs based on the magnetic field, high-Jc Nb3Sn strand is applied for the high-field sub-WP, and ITER type Nb3Sn strand and NbTi strand are applied in mid and low field sub-WPs, respectively. Stability and quench analysis of the TF coil system in CFETR have been performed. This analysis utilizes the 1-D code “GANDALF.” The stability simulations consider multiple scenarios applied to the superconducting cable during the most critical operating conditions to thoroughly examine the minimum quench energy and temperature margin against short-term mechanical and long-term electromagnetic disturbances.
A probe method for measuring the ion current density and theoretical calculations of the dynamics of neutral and charged plasma particles using the ionization region model (IRM) is used to study short and ultra-short pulse high-power impulse magnetron sputtering (HiPIMS). This paper studies reasons for the increase in the average ion current density on the substrate at shorter pulses, when the average discharge power does not change. HiPIMS pulses are applied to the copper target at constant values of average discharge power (1000 W) and peak current (150 А), respectively, while the pulse time of the discharge voltage ranges from 4 to 50 µs. A power supply with low output inductance is designed to generate ultra-short pulses. It is shown that shorter discharge pulses lead to a multiple growth (from 2 to 7 mA cm−2) in the average ion current density on the substrate and a growth in the peak intensity of Ar+, Cu+ and Cu2+ recorded by optical emission spectroscopy. A theoretical model of this effect is based on the spatially averaged IRM, which considers afterglow effects. According to theoretical calculations, the increase in the average ion current density on the substrate is determined by the plasma dissipation in the ionized region after the pulse ends. Also, a decrease in the copper deposition rate from 180 to 60 nm min−1 with decreasing pulse time from 40 to 4 µs is explored. A comparison of experimental data with those obtained earlier shows that the suggested dependences of the ion current density and deposition rate on the HiPIMS pulse time are typical for discharge systems with different cathode materials and configurations, i.e., for single- and dual-magnetron systems. This indicates a common nature of the phenomena observed and additionally confirms the results obtained.
When voltage is applied between two electrodes situated in close proximity to each other (10–100 μm), a weakly ionized, low temperature plasma discharge can be generated. This in turn creates a plasma sheath, an electrically ionized boundary layer (typically of the order of 10’s to 100’s of microns), where space charge effects dominate. The sheath acts like a virtual capacitor, with the plasma behaving as an inductor. Aerodynamic effects influence the plasma morphology (shape, thickness), thus making the plasma the transduction mechanism. The attraction to the use of plasma discharge as a transduction method for fluid flow property measurement stem from the fact that it lends itself to a probe implementation that is simple in design, can be miniaturized, and at the same time offers unmatched capability for handling ultra-high temperature environments. Sensing plasma discharge characteristics and their variation due to flow interaction can be done electrically, but also optically to yield time-varying intensity and spectral information from fluid-plasma interaction. The current paper focuses on the deployment of a micro-plasma sensor system as a new novel multi-parameter sensing approach for surface flow measurement. Results on pressure dynamics, shear flow, and other possible engineering parameters will be discussed in the context of results from several bench-level experiments.
The current integration state of ITER Equatorial Port #11 (EP#11) is described. This port is the first plasma port and thus the integration phase is close to the final stage. The new modular design of neutron shielding is implemented in the Diagnostic shielding modules’ (DSM) construction to achieve the maximum shielding efficiency within the weight restrictions and keeping fully operable the tenant diagnostics systems. The same approach was applied to Interspace structure frame design to allow the safe hand-on maintenance near the highly activated components. The current iteration of the engineering calculations, including the neutron transport and shutdown dose rate (SDDR), thermohydraulics, electromagnetics, seismic, and structure integrity calculations, showed that the current design of EP#11 satisfy all ITER requirements. The special metalworking, welding, and various other technologies are tested during the process of preparation for the manufacturing of ITER EP#11. Production technologies of the full-size DSM mock-up and various elements of its infrastructure were tested. The multizoned clean area assembly hall for the final assembly is close to getting completed and the testing of vacuum items has to be sent to ITER.
Time-varying structures are frequently observed in non-equilibrium systems. Magnetically confined plasma is a typical non-equilibrium system. The spatial inhomogeneity of plasma, which is produced and sustained by external sources, excites instabilities in the plasma. In turn, transport driven by the instabilities tries to mitigate the plasma’s inhomogeneity. As a result, spatial gradients, waves, flows and eddies coexist in the plasma and interact with each other causing the plasma to become turbulent [1, 2]. Due to the various nonlinearities in plasma, multi-scale spatiotemporal structures can form in the plasma turbulence [3]. The identification of the spatiotemporal structures in plasma turbulence is essential for visualizing their coarse-grained nature, where many decomposition techniques have been applied to time-series data of plasma turbulence [4, 5]. Fourier analysis is frequently used as a decomposition technique, however, ensemble averaging is required when it is applied to random signals. Usually, ensemble averaging is replaced by time averaging [6], which can mask the non-stationarity of the signals. Actually, structure in plasma turbulence varies in time [7], and thus new analysis tools, which can extract the non-stationary spatiotemporal structure of the turbulence, are required. Here we apply a dynamic mode decomposition (DMD) analysis to signals of turbulence in a magnetized laboratory plasma. Laboratory plasma is very useful as it allows us to verify the capability of our method, and because it has excellent reproducibility and controllability and allows for multi-point simultaneous measurements to be made. Since it was introduced in 2008 [8], DMD has been applied to fluid flow studies especially in analyses of nonlinear dynamics [9, 10]. From the spatiotemporal data obtained from an experiment or a numerical simulation,
The paper presents the results of applied research on the design and application of an integrated platform for solving applied problems of developing, studying and optimizing high-power electron-plasma devices from the centimeter to THz range based on the results of previous fundamental and exploratory research.