Resonance Layer Research Articles

A Mixed Method for Feature Extraction Based on Resonance Filtering

Machine learning tasks such as image classification need to select the features that can describe the image well. The image has individual features and common features, and they are interdependent. If only the individual features of the image are emphasized, the neural network is prone to overfitting. If only the common features of images are emphasized, neural networks will not be able to adapt to diversified learning environments. In order to better integrate individual features and common features, based on skeleton and edge individual features extraction, this paper designed a mixed feature extraction method based on resonance filtering, named resonance layer. Resonance layer is in front of the neural network input layer, using K3M algorithm to extract image skeleton, using the Canny algorithm to extract image border, using resonance filtering to reconstruct training image by filtering image noise, through the common features of the images in the training set and efficient expression of individual characteristics to improve the efficiency of feature extraction of neural network, so as to improve the accuracy of neural network prediction. Taking the fully connected neural network and LeNet-5 neural networks for example, the experiment on handwritten digits database shows that the proposed mixed feature extraction method can improve the accuracy of training while filtering out part of image noise data.

Iodine electron cyclotron resonance plasma source for electric propulsion

With the rapid development of commercial space in recent years, the low-power and low-cost propulsion systems are needed more and more urgently. Compared with conventional chemical propulsion, electric propulsion has a higher specific impulse. Compared with the conventional xenon propellant, iodine propellant that does not require high pressure storage, is cheap and close to the relative atomic mass and ionization energy of xenon. Electron cyclotron resonance source has the advantages of no internal electrode, low pressure ionization, high plasma density and compact structure, which is suitable for low power electric propulsion. Therefore, the study of low power iodine propellant electron cyclotron resonance plasma source is of great significance. In this study, a set of corrosion-resistant feed system with balanced and stable output of iodine vapor is designed. Then the iodine-corrosion-resistant electron cyclotron resonance thruster is designed completely. A corrosion-resistant coaxial cavity structure is used to feed the microwave to the thruster, and the channel magnetic field is changed into a cusped field to generate more electron cyclotron resonance (ECR) layers. Finally, the combined ignition experiment is successfully conducted, showing the first plasma source using electron cyclotron resonance to ionize iodine propellant that can be used for electric propulsion in the world. The analyses of experiments, static magnetic field, microwave electric field distribution show that the unstable plasma plume scintillation at low power and low flow is caused by the conversion between ordinary wave electron plasmon resonance heating mode and extraordinary wave electron cyclotron resonance heating mode. The decrease of ionization rate at a high flow rate is caused by electron loss, wall loss and electronegativity of iodine propellant. Based on this principle, an improvement scheme is proposed. The plasma source has no obvious damage after discharge, which indicates that it has the potential of long life. This work preliminarily proves that the low power electron cyclotron resonance electric propulsion scheme of low power iodine propellant is feasible.

Calculations for the optical system for the first ITER plasma

A dedicated optical system is designed for the breakdown of the first ITER plasma, when the machine will not be equipped with the equatorial ECRH-launcher. Seven beams from the upper launcher will be transmitted via several in-vessel mirrors through the resonance layer to a beam-dump. The whole system was simulated with the PROFUSION package to obtain the beam parameters, estimate spill-over effects and determine the required polarization in the launcher in order to have X-mode polarization in the resonance.

Reconfigurable Bidirectional Beam-Steering Aperture With Transmitarray, Reflectarray, and Transmit-Reflect-Array Modes Switching

The design and experiment of an electronically reconfigurable bidirectional spatially-fed array are presented, which combines the functionalities of reconfigurable transmitarray (TA), reflectarray (RA), and transmit-reflect array (TRA). First, we demonstrate a novel bidirectional unit cell composed of a tunable resonant layer between a pair of orthogonally oriented metal gratings. Two positive-intrinsic-negative (PIN) diodes are integrated into the tunable resonant layer to achieve the 1-bit phase resolution in either transmission or reflection mode. Based on the proposed unit cell, a 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times16$ </tex-math></inline-formula> -element array arranged in a square grid, which can be controlled independently by a field programmable gate array (FPGA)-based digital control circuit, is excited by a linearly-polarized horn to show the beam steering ability of reconfigurable TA and RA. To realize TRA function integration with the bidirectional beam independent steering simultaneously, the method based on superposition of the aperture fields (SAF) on the aperture is used. In SAF design, the entire aperture is divided into transmission and reflection modes co-existing, and the arrangement and phase distribution are optimized by particle swarm optimization (PSO) algorithm to achieve minimum sidelobe levels (SLLs) and peak gain of bidirectional beam. The measured results of the prototype demonstrate that the antenna can steer bidirectional beam both in simultaneous and time division operating modes, which is not reported to the best of the authors’ knowledge. Our proposed method opens a new avenue for the design of high-performance multifunctional reconfigurable antenna systems.

Study on the effect of discharge chamber length on the performance of electron cyclotron resonance ion thruster

Discharge chamber length is one of the factors in optimizing the electron cyclotron resonance ion thruster performance. It adjusts the distance between bulk plasma and grid system to change the plasma density upstream of the screen grid, which will affect the ion beam current and focusing state to achieve optimization purpose. However, new evidence shows the discharge chamber length plays an important role in ionization during ion beam extraction, which means that the effect of discharge chamber length on the performance of electron cyclotron resonance ion thruster should be reexamined. After applying grid voltages, another high electron temperature region located upstream of the screen grid is observed in the integrated simulation using particle-in-cell with Monte Carlo collision method, but it is not observed in the traditional discharge chamber simulation. It is believed in the paper that the high electron temperature region exists objectively, because the Child-Langmuir sheath will repel electrons moving towards screen grid back to magnetic mirrors again. Those electrons will gain energy from microwave, and finally form a high electron temperature region along the Child-Langmuir sheath. This phenomenon implies that discharge chamber length can adjust the high electron temperature distribution upstream of screen grid to affect the plasma generation. Therefore, in this work, the effect of discharge chamber length on discharge and ion beam performance is systematically studied by adopting the integrated simulation. In this paper, three ion thrusters with different discharge chamber lengths are simulated. Under the conditions of same magnetic field and operation parameters, the comparisons of electron energy gain, plasma parameter distributions and ion beam current among the three ion thrusters are conducted. The results show that shorter discharge chamber length has higher electron energy gain, plasma density and voltage, but smaller ion beam current. This abnormal phenomenon can also be seen experimentally. By analyzing the ionization rate inside the chamber, it can be seen that high-temperature electrons upstream of the screen grid have a significant contribution to ionization. And thus, a little bit longer discharge chamber length with lower plasma density inside the chamber has bigger ion beam current for having higher plasma density upstream of the screen grid. According to this phenomenon, an electron heating mode is proposed: electrons gain energy by reciprocating through the electron cyclotron resonance layer between the Child-Langmuir sheath and magnetic mirrors. This heating mode can be used as a supplement to the electronic constraints outside the magnetic mirrors to improve the energy utilization efficiency of the thruster, which can provide a new insight into the electron cyclotron resonance ion thruster design in the future.

A transparent water-based metamaterial broadband absorber with a tunable absorption band

In this study, a tunable and optically transparent water-based wideband metamaterial absorber (MMA) is proposed and verified. By adjusting the thickness of the water layer, the conversion of the absorber absorption band from 7.4–22.4 GHz to 23.1–35.5 GHz can be achieved, which demonstrates the flexibility of MMA. Indium tin oxide (ITO) as the resonant and reflective layers of the material structure. Optically transparent polymethyl methacrylate (PMMA) is used as a medium container to encapsulate the water. Furthermore, the suggested MMA is polarization insensitive and has broad incident angle stability. Experiments verify the excellent properties of the proposed MMA. As a result, the suggested MMA has various applications in military and medical equipment optical windows.

Numerical Investigation of the Ion Cyclotron Resonance Heating (ICRH) Physics in DTT

An extensive linear analysis of the ICRH propagation and absorption in DTT full heating scenario has been performed by means of three advanced numerical tools: DISEMAG, FELICE and TORIC. The numerical codes solve respectively the full dispersion relation in the complex domain of the wavenumber (DISEMAG) and the integro-differential equation that accounts for the correct evaluation of the ICRH power absorption in a slab plasma (FELICE) and in the tokamak equilibrium configuration (TORIC). Moreover, by incorporating the antenna conceptual design, as released by the engineering design team, in FELICE and TORIC, the power spectrum, radiated by the antenna (3 straps) and coupled to the plasma, has been evaluated in the case of 60 and 90 MHz (3He and H minority heating respectively). By extensively using the abovementioned suite of codes, and after establishing the plasma target (fixing tokamak dimensions, density, temperatures, plasma current, magnetic field, isotopic composition, etc.), and the antenna characteristics (number, dimension, pitch, and radial position of the straps, antenna size, etc.), the power absorption on the various species (electrons, majority and minority ions) has been calculated as function of the minority concentration, parallel wavenumber, frequency, harmonic resonant layer, etc.. Comparison between the codes DISEMAG and TORIC in evaluating the absorption on electrons and minority ions has also been performed and shows a good agreement of the results. A new ion heating scheme based on three ions mixture has also been proposed in DTT.

A novel dual‐band miniaturized frequency selective surface with high selectivity

AbstractIn this paper, a novel dual‐band multilayer frequency selective surface (FSS) with high selectivity and miniaturization characteristics is proposed. The FSS consists of a top and bottom resonant layer and an intermediate coupling layer. The top and bottom resonant layers provide dual‐band passbands, and the cross‐coupling between the three layers makes the structure produce four transmission zeros (TZs) distributed two‐by‐two on both sides of the passband to improve the sharp roll‐off characteristics of the structure. Use bent structures in the top and bottom layers of the cell design to achieve miniaturization of the elements. FSS provides stable performance in incident angles from 0° to 45° with different polarizations of incident waves (TE and TM wave). The lower band of FSS works at 9.1 GHz and the higher band works at 10.26 GHz, the cell size of FSS is , FSS samples were made and tested, and the test results fit well with the simulation results.

First results of fast visible imaging diagnostic in Aditya-U tokamak.

A Fast Visible Imaging Diagnostic (FVID) system, measuring the visible light emission spectrum (400-1000nm) from tokamak plasma, has been installed on the Aditya-U tokamak to monitor the two-dimensional dynamics of the poloidal cross section of the plasma. In this work, we present the design and installation of the FVID system on the Aditya-U tokamak. The evolution of plasma and plasma-wall interactions is described. The signature of the runaway electron beam in visible imaging and its correlation with other diagnostics is presented. The estimation of the electron cyclotron resonance layer position during pre-ionization is also discussed in this work.

DIII-D Electron Cyclotron Heating and Current Drive System Status and Plans

The DIII-D 110-GHz electron cyclotron heating and current drive (ECH/ECCD) system supports a wide range of experiments at the DIII-D National Fusion Facility and is pioneering innovative new techniques for future fusion reactors. The system currently includes eight sockets with four installed gyrotrons, 31.75-mm circular corrugated transmission lines, and four dual real-time steerable launchers plus two top launchers (TLs). After the successful testing of the first TL, this injects the EC waves downward nearly parallel to the resonance layer with double current drive efficiency and a long absorption path, and a second new TL was designed and installed with an upgraded design. Some of the operational limitations encountered for the 110-GHz X-mode second harmonic resonance scenario launched in overdense plasmas were overcome with the alternative use of O-mode second harmonic launch. Two new gyrotrons in a new series manufactured by Communications and Power Industries (CPI) were installed and tested, bringing up the total installed power to 3 MW. The installation of repaired and new gyrotrons will increase the number of installed gyrotrons to 7 in 2023. An addition to the DIII-D building will be completed in early 2022 to provide the space to expand the ECH/ECCD system to ten gyrotron systems plus an extra gyrotron test socket.

Multilayer transparent bendable broadband microwave absorber covering the frequency band near 5 GHz

A multilayer transparent microwave absorber that possesses a broadband, is bendable, and covers the frequency band near 5 GHz is proposed in this work. The absorber uses three layers of 110 Ω/sq etched patterned indium–tin–oxide-polyethylene terephthalate (ITO-PET) films as the resonant layers. The infinite cycle structure of the absorber is simulated by using the CST STUDIO SUITE. The absorber shows &gt;90% absorption effect in the frequency band 4.16-7.48 GHz and a 99% absorption effect in the band near 5 GHz (4.98-5.83 GHz). Furthermore, by replacing the intermediate medium with polydimethylsiloxane (PDMS), the absorber obtains excellent bendability characteristics.

Changes in optical thicknesses of Ge and SiO thin films and spectral characteristics of narrowband filters at cryogenic temperatures

Subject of study. Two narrowband filters with Ge and SiO resonant layers were investigated both at room and cryogenic temperatures of 293 and 80 K, respectively. Aim of study. The deposition of bandpass filters with predefined deviations of optical thickness layers under operating conditions at cryogenic temperatures was considered. The presented design of an optical interference coating increases the transmission coefficient in the operating spectral ranges during its operation at cryogenic temperatures. Method. An antireflective bandpass coating constituting a pair of Ge-SiO film-forming materials was deposited onto a substrate made of an optical material using vacuum deposition. The layer thicknesses were controlled during their deposition using an optical control system. Main results. The obtained spectral characteristics of two narrowband filters are presented herein. The optical thicknesses of the filters with resonant layers made of Ge and SiO and thickness variations at the temperatures of 293 and 80 K were determined by an iteration method via the positions of the wavelengths of maximum transmission of the filters. Practical significance. The spectral characteristics of the filters with SiO resonant layers demonstrated smaller changes at cryogenic temperatures than those of the filters with Ge resonant layers.

Determination of best operation parameters of electron cyclotron wall conditioning in KSTAR

Dependence of EC injection power (0.6 and 1.4 MW), EC injection width (0.1–1.0 s) and prefilled He pressure ( 2 . 8 × 1 0 − 5 ∼ 2 . 2 × 1 0 − 3 mbar) on D 2 outgas efficiency is investigated at a toroidal field of 2.4 T in a poloidal trapped particle configuration with an EC wave frequency of 140 GHz (X-mode) and a second harmonic resonance layer near the machine center (1.73 m). With increasing EC injection power, D 2 outgas increases clearly. The dependence of the EC power injection is the most pronounced between the scanned parameters. It is found that an optimum prefilled He pressure for D 2 outgas exists under the condition of a constant EC injection power. It is observed that both high EC injection power and the optimum prefilled He pressure enhance the ion flux to the center stack, suggesting that the D 2 outgas originates from the center stack. • Parameter scan (prefilled He pressure, EC pulse width, EC power) was performed to determine best ECWC parameters in KSTAR. Within this experiment. • In terms of D 2 removal efficiency, optimum He pressure existed, higher EC injection power was better but EC injection length was less effective. • It was suggested that D 2 outgassing originated from the center stack. • The reason why ECWC at highest He pressure with very small D 2 outgassing resulted in successful burn-through was still unclear.

A metal hybrid resistive film ultra-wideband metamaterial absorber for infrared region

An ultra-wideband metamaterial absorber (MA) based on the resistive film is proposed. Unlike conventional MAs based on the resistive film, the proposed absorber features a hybrid resonant layer of resistive film and metal patch at the same top layer. The absorption of the proposed absorber exceeds 90% over the ultra-wideband frequency range of 20 –220 THz, covering most of the infrared region, while the relative absorption bandwidth is up to 167%. The coupling of resistive film and metal pattern at the same layer plays the significant role in enhancing the absorption performance, which is interpreted by the investigation of the surface current distribution. Moreover, the absorber is insensitive to polarization and incident angle. The proposed absorber with high absorption capability as well as simple and compact structure is a proper candidate for the applications in the infrared frequency regime.

Multi-harmonic electron cyclotron heating and current drive scenarios for non-inductive start-up and ramp-up in high field ST-40 spherical tokamak

Non-inductive start-up and ramp-up is an important topic for spherical tokamak reactor design as the central solenoid implementation is highly restrictive particularly for the low-aspect-ratio tokamak configuration. In the high field spherical tokamak (ST), ST-40 with B T0 ⩽ 3 T, a preparation is underway for high power ECH and ECCD current start-up/ramp-up experiments utilizing two MW-class 140/105 GHz gyrotrons. Here, we explored various ECH/ECCD scenarios for a low-field-side (LFS) launch-angle steerable waveguide launcher placed near the mid-plane region. Due to the large toroidal field variation of ST configuration, multiple cyclotron harmonic resonance layers could exist within the plasma. In this start-up and ramp-up regime, both fundamental and second harmonic ECH resonances must be considered. We find that even with the presence of X-II resonance layer in the plasma, an efficient X-I ECH and ECCD regime can be accessed for the low electron temperature T e0 as low as 200 eV which is a typical starting temperature of ECH heated plasmas in an open-field-line configuration. The presence of X-II resonance could become significant at higher T e0 as X-II absorption increases with T e0 which could reduce the current ramp-up efficiency as the power reaching X-I is reduced. Finally for the pure X-I regime where the 2Ωe resonance is moved outside the plasma with B T0 ∼ 3.4 T, we find that it is possible to reach the full current of I p ∼ 1 MA fully non-inductively with the ECH power of ∼1 MW at n e0 ∼ 1.0 × 1019 m−3 using 105 GHz frequency gyrotron. By reducing the outer limiter position R L ∼ 78 cm to 70 cm, the pure X-I regime is recovered at the rated ST-40 magnetic field of B T0 ∼ 3.0 T. This X-I regime is accessible with a relatively broad range of launched n II or the launching angles. A survey of X-mode X-II ECH and ECCD at higher density regimes is also shown for completeness.

Reflectivity spectra as absorption resonant spectra: is it correct?

Approximate expressions for X-ray resonant and Mössbauer reflectivity in the total external reflection region are developed for the limiting cases of a semi-infinite mirror with a small resonant addition to the total susceptibility and for the case of an ultrathin resonant layer. It is shown that in this region the reflectivity can depend linearly on the imaginary part of the refraction index; therefore in these cases the consideration of reflectivity spectra (R-spectra) as absorption resonant spectra, taken up in several experimental studies, can be justified. However, several effects producing dispersive distortions of the R-spectrum shape, even for very small grazing angles, have been found. It has been shown that dispersive corrections to the R-spectrum shape are mostly necessary if the non-resonant absorption is relatively large. Model calculations demonstrate that the quantitative spectroscopic information extracted from R-spectra using the software developed for absorption spectra can be inaccurate.

Highly Sensitive Terahertz Dielectric Sensor for Liquid Crystal

This paper presents the design and process of two highly sensitive sensors working in the terahertz band. The sensors comprise the quartz substrate, medium, reflection plate, and metal resonant layer with a symmetrical single-slot patch array. The devices help study the electrically induced permittivity of two liquid crystals in different frequency bands and at different voltages, and the experimental data verify that both liquid crystals have a large birefringence. Based on experimental results, the sensitivity of the fabricated sensor is 47.03 GHz/RIU in the frequency range 90–140 GHz. Similarly, the other fabricated sensor has a sensitivity of 112.47 GHz/RIU in the frequency range 325–500 GHz. The results show that both sensors have superior sensing properties and potential applications in biological and chemical liquid sensing.

Analysis of synthetic electron cyclotron emission from the high field side of HL-2M tokamak plasmas.

A synthetic electron cyclotron emission (ECE) diagnostic is used to interpret ECE signals from preset plasma equilibrium profiles, including magnetic field, electron density, and electron temperature. According to the simulation results, the electron temperature (Te) profile covering the harmonic overlap region can be obtained by receiving ECE signals at the high field side (HFS) of the HL-2M plasma. The third harmonic ECE at the low field side (LFS) cannot pass through the second harmonic resonance layer at the HFS unless the optical thickness (τ) of the second harmonic becomes gray (τ ≤ 2). In addition, the impact of the relativistic frequency down-shift has been evaluated and corrected. The measurable range of the HFS ECE has been calculated by scanning different parameters (electron density, temperature, and magnetic field). Higher plasma parameters allow a wider radial range of electron temperature measurements. The minimum inner measurable position can reach R = 120cm (r/a = -0.89) when the product of core temperature (Te0) and density (ne0) is greater than 35 × 1019keVm-3, which is extended by more than 30cm inward compared with that of the LFS measurement. The HFS ECE will greatly improve the diagnostic ability of ECE systems on the HL-2M tokamak.

Parametric dependencies of resonant layer responses across linear, two-fluid, drift-MHD regimes

Non-axisymmetric magnetic fields arising in a tokamak either by external or internal perturbations can induce complex non-ideal MHD responses in their resonant surfaces while remaining ideally evolved elsewhere. This layer response can be characterized in a linear regime by a single parameter called the inner-layer Δ, which enables outer-layer matching and the prediction of torque balance to non-linear island regimes. Here, we follow strictly one of the most comprehensive analytic treatments including two-fluid and drift MHD effects and keep the fidelity of the formulation by incorporating the numerical method based on the Riccati transformation when quantifying the inner-layer Δ. The proposed scheme reproduces not only the predicted responses in essentially all asymptotic regimes but also with continuous transitions as well as improved accuracies. In particular, the Δ variations across the inertial regimes with viscous or semi-collisional effects have been further resolved, in comparison with additional analytic solutions. The results imply greater shielding of the electromagnetic torque at the layer than what would be expected by earlier work when the viscous or semi-collisional effects can compete against the inertial effects, and also due to the intermediate regulation by kinetic Alfvén wave resonances as rotation slows down. These are important features that can alter the non-axisymmetric plasma responses including the field penetration by external fields or island seeding process in rotating tokamak plasmas.

Resonant Atmospheric Plasma-Sprayed Ceramic Layers Effectively absorb Microwaves at 170 GHz

Microwave absorbing layer materials (MALMs) are extremely important for many components in fusion reactors to absorb microwave radiation in a controlled manner and with predictable power density. Therefore, a detailed knowledge of absorption properties of absorber coating materials used is necessary. Plasma-sprayed mixed oxide coatings are most commonly used in those applications where moderate power density is expected. In this paper, a plane wave absorption model is presented using refractive index and absorption coefficient as internal parameters and incidence angle, polarization, and layer thickness as external parameters. The model has been calculated assuming radiation of 170 GHz, as envisaged for the ITER research facility. Three atmospheric plasma-sprayed coating materials were considered in this work: titanium dioxide (TiO2), chromium oxide (Cr2O3), and a mixed aluminum-titanium oxide Al2O3-TiO2 (40/60). Theoretical results are compared with free wave measurements with two antennas. Different coating thicknesses have been prepared and measured in different polarization and incidence angles. Results are discussed regarding polarization, incidence angle, layer thickness, absorption coefficient, and refractive index.