Metal Wall Research Articles

Access to an ELM-suppressed X-point radiator regime in TCV snowflake minus configurations

TCV’s operating regime with an X-point radiator (XPR) has been broadened by changing the magnetic geometry. XPRs have properties that could make them an attractive power exhaust solution for fusion reactors. These include the conversion of a high fraction of exhaust power into radiation. TCV had previously accessed the XPR regime only with difficulties, as predicted for plasmas where radiative losses are dominated by carbon impurities, that are ubiquitous in TCV. Guided by this theoretical model of the XPR, recent experiments employed TCV’s configurational versatility to demonstrate that XPR access can be facilitated by introducing a second X-point in the vicinity of the separatrix. This configuration, which has a snowflake-minus topology, features a particularly long magnetic connection length from the region just above the X-point to the outer midplane together with a wide geometrical interface with the private flux region that reaches high neutral pressure. Transitioning to this configuration in a high-power H-mode leads to a shift in the radiating region across the separatrix from the divertor to a volume above the X-point, i.e. within the last closed flux surface (LCFS). This displacement of the radiating region is co-incident with the disappearance of edge localised modes (ELMs), while retaining H-mode confinement, a behaviour only, to date, observed in devices with metallic walls. In contrast to observations in these other devices, on TCV, the primary strike points in these configurations remain attached. Detailed measurements of the plasma kinetic parameters inside and outside of the separatrix now challenge the models for access and stability of the XPR and ELMs alike.

Simulating conjugate heat and mass transfer by the advanced perforated wall model for effusion cooling

Full-scale Computational Fluid Dynamics (CFD) numerical simulations can accurately predict the heat flux and metal wall temperature of gas turbine combustor liners, but they require considerable computational resources. In present work, an Advanced Perforated Wall model (A-PWM) has been developed to resolve the flow and heat transfer behaviors in this confined region. The geometric structure of the effusion cooling perforated plate is simplified, while the fluid-solid coupling heat transfer processes are still fully considered in details. The three-dimensional Reynolds Average Navier–Stokes simulations have been carried out for both a single-hole cooling plate and a multi-hole perforated cooling plate by using A-PWM. For simulations of the single-hole cooling plate, the cooling effectiveness in the downstream of the jet flow with the x/D ranging from 2 to 8 predicted by A-PWM shows good agreement with conjugate heat transfer model and experimental results. For multi-hole perforated cooling plate, the differences of cooling effectiveness between the prediction results by A-PWM and experimental results are just within 5%, confirming the developed model’s accuracy in predicting the effusion cooling. In addition, the A-PWM can also be employed to analyze the temperature distribution inside the solid zone. In simulations of both the single-hole cooling plate and the multi-hole perforated cooling plate, the use of the A-PWM model can lead to a reduction of over 35% in grid count compared to the conjugate heat transfer model, significantly reducing the computational time.

Fuel recycling feedback control via real-time boron powder injection in EAST with full metal wall

Fuel recycling feedback control via real-time boron powder injection in EAST with full metal wall

Overview of damage to beryllium limiters by unmitigated disruptions and runaway electrons in the JET tokamak with metal walls

Abstract The Joint European Torus (JET) fusion reactor was upgraded to the metallic wall configuration in 2011 which consisted of bulk beryllium (Be) tiles in the main chamber and bulk tungsten (W) and W-coated CFC tiles in the divertor [1]. During each campaign, a series of wall damages were observed; on the upper dump plates (UDP) positioned to the top part of the vessel walls and on the inner wall - mainly affecting the inner wall guard limiters (IWGL). In both cases, it was concluded that the causes of these damages were unmitigated plasma disruptions. In the case of JET with the metallic wall configuration, most of these plasma disruptions were intentionally provoked. The overall objective was to study the behaviour of these phenomena, in order to assess their impact on the wall, improve understanding of morphological material changes, and – based on that - to develop, implement and test mitigation techniques for their prospective use on ITER. The current results bring additional information on the effects of the unmitigated plasma disruptions on the UDPs and are a significant extension of work presented in [2] where the scale of the damage after three operational campaigns on the Be top limiters of JET was highlighted. In addition, new data is presented on the damaging effect that the high energetic runaway electrons had on the Be IWGL in JET.

Wire-arc-additively manufactured Bi metallic structure: Mechanical properties and microstructural characterization

In this investigation, the fabrication and mechanical properties of Bi metallic structure walls produced using wire-arc-additive manufacturing (WAAM) technique, employing stainless steel (SS) 316L and 304 filler wires, are examined. The findings reveal that SS 304 exhibits superior mechanical attributes compared to SS 316L, notably showcasing impressive tensile strength and exceptional ductility. Bi metallic structure, meticulously constructed using both SS 316L and SS 304 filler wires, effectively replicates these distinctive mechanical properties, rendering it highly desirable for application prioritizing mechanical performance. The observed enhancement in strength is attributed to variations in microstructure resulting from a complex thermal history. Microstructural and crystallographic analyses of Bi metallic structure are conducted using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscattered diffraction spectroscopy (EBSD), and X-ray diffraction spectroscopy (XRD). Additionally, tensile strength (TS) of Bi metallic structure surpasses that of WAAM SS 316L by 3.95%. This comprehensive research not only elucidates the intricate process of material selection in additive manufacturing but also underscores the significant potential of Bi metallic structure in meeting the stringent demands of engineering applications requiring exceptional mechanical properties.

A long-pulse small edge-localized-mode high-confinement plasma with detachment feedback control by floating potential in an experimental advanced superconducting tokamak in a metal wall environment

Abstract One of the key challenges facing the magnetic fusion research is to demonstrate the compatibility between high confinement and radiative divertor in long-pulse discharges with a metal wall environment. A small edge localized mode (ELM) high confinement plasma is obtained in the upgraded lower divertor of Experimental Advanced Superconducting Tokamak (EAST) with an energy confinement factor H98~1.1 and a Greenwald density fraction fGW ~ 0.65 maintained for 26 s, and periodical detachment is achieved through active control of neon impurity seeding in this long-pulse discharge. For the divertor region, partial detachment is achieved periodically on the outer divertor target plates with the plasma temperature near the outer strike point decreased to below 5 eV and peak surface temperature on the outer divertor target plates maintained below 350C. The peak heat flux of the lower outer divertor decreases significantly and its profile along the target becomes very flat in the detached state. Two low-frequency (<10 kHz) fluctuations that are related to rippling mode caused by a resistive instability appear in the detached state. For the pedestal region, the electron pressure profile is flatter and ELM amplitude is smaller in the detached state than that in the attached state. Edge coherent mode (ECM) appears in the attached state and disappears in the detached state. To achieve this experimentally, a new impurity seeding feedback control scheme is applied, where the floating potential measured by divertor Langmuir probes is used as the feedback sensor, which is more reliable in the long-pulse discharges with high heat fluxes, thus more suitable for application in future devices. This work provides a new approach for the actively controlled radiative divertor as a solution to the divertor heat loads of the future fusion reactors.

Stress state of billet – mandrel system during production of hollow steel billet in a unit of continuous casting and deformation. Part 2

The paper presents the results of theoretical research of stress-strain state of a billet – mandrel system when producing steel hollow billets in a unit of combined continuous casting and deformation, in which the working surface of the calibrated anvils are made with a variable radius. The necessity of making the working surface of the calibrated anvils with a variable radius is substantiated and initial data for the calculations is given. The calculation results are considered along the lines of the volumetric model passing through the characteristic points of deformation centers. The authors determined the forces when the anvils compress the wall of a hollow billet and the force of pulling the hollow billet from the mold. The laws of metal axial displacements and stresses in the deformation centers during compressing the wall of a hollow billet was established at the combined process of continuous casting and deformation in the unit. Nature of the stressed state of the metal wall of a hollow billet is considered from the perspective of improving its quality. The technique studied allows to determine the stress-strain state of a mandrel when producing a hollow steel billet using such a unit. The authors provided the recommendations for reliable gripping and compression with calibrated anvils of a hollow steel billet coming from a water-cooled copper mold of the unit of combined continuous casting and deformation.

Revealing ancient technology: a high-energy X-ray computed tomography examination of a Mesopotamian copper alloy head

Although the origins of lost wax casting extend back into the 5th millennium BCE, it was not until the development of hollow core casting that life-sized metal sculptures could be produced. Based on existing evidence, the earliest adoption of this technique, which involves the inclusion of a clay core within a wax model, occurred in Iraq (Mesopotamia) during the Early Dynastic III period (ca. 2600–2350 BCE). To date, only one hollow core casting from the succeeding Akkadian period (ca. 2350–2150 BCE)—the Sargon Head in the collection of the Iraq Museum—has been studied from a technical point of view. The recent attribution of The Metropolitan Museum of Art's Head of a ruler to this formative period of hollow core lost wax casting provided the impetus for its examination by high-energy X-ray computed tomography—the most practical technique for an object that is continuously on display that could image in 3D the interior morphology of this sculpture given the considerable thickness of its metal walls. This scan revealed a markedly different style of production than the Sargon Head. Although further research on early castings is required to determine the chronological implications of the differences observed and to elucidate more generally the early development of hollow casting technology, the scan of the Head of a ruler provides evidence of some of the challenges encountered and problem-solving strategies used in the casting process.

Overview of the KSTAR experiments toward fusion reactor

Abstract The KSTAR has been focused on exploring the key physics and engineering issues for future fusion reactors by demonstrating the long pulse operation of high beta steady-state discharge. Advanced scenarios are being developed with the goal for steady-state operation, and significant progress has been made in high ℓi, hybrid and high beta scenarios with βN of 3. In the new operation scenario called FIRE, fast ions play an essential role in confinement enhancement. GK simulations show a significant reduction of the thermal energy flux when the thermal ion fraction decreases and the main ion density gradient is reversed by the fast ions in FIRE mode. Optimization of 3D magnetic field techniques, including adaptive control and real-time machine learning (ML) control algorithm, enabled long-pulse operation and high-performance ELM-suppressed discharge. Symmetric multiple shattered pellet injections and real-time DECAF are being performed to mitigate and avoid the disruptions associated with high-performance, long-pulse ITER-like scenarios. Finally, the near-term research plan will be addressed with the actively cooled tungsten divertor, a major upgrade of the NBI and helicon current drive heating, and transition to a full metallic wall.

Uniformity improvement of microwave heating with switchable frequency selective surface

Microwave heating has attracted interests in many industrial applications, yet heating inhomogeneity remains a critical issue. This study proposes a novel approach to enhance microwave heating uniformity employing a switchable frequency selective surface (FSS). The PIN diodes in each FSS unit cell can be toggled ON or OFF by controlling voltage biases, enabling the FSS to either reflect or transmit incident electromagnetic waves. Placing this switchable FSS in front of a heating cavity wall creates a dynamic reflecting boundary, which, through periodic alterations of the FSS and metallic wall, effectively improves the heating uniformity. To validate this method, we simulated the heating of a potato sample at 2450 MHz using COMSOL Multiphysics and conducted experimental tests. Both simulation and experimental results demonstrate that the proposed method significantly enhances microwave heating uniformity across various materials and sample sizes. This work provides a promising solution for designing microwave heating reactors.

ОБЛАДНАННЯ ВХІДНОЇ МАГНІТНО-КАВІТАЦІЙНОЇ ПІДГОТОВКИ ВОДИ ДЛЯ ТЕПЛОМЕРЕЖ

If high-quality water treatment for boilers is not organized, the impurities present in untreated water lead to a number of problems: large colloidal and mechanical impurities in the form of scale, rust, clay or sand quickly clog the pipes, significantly reducing their internal diameter. This causes the failure of shut-off valves and pumping equipment: hardness salts and other poorly soluble salts (carbonates, magnesium and calcium sulfates, silicates, various compounds of copper and manganese) settle, creating a crust on the metal walls of the equipment, which reduces its heat output. This contributes to a reduction in boiler power, increases energy costs, and significantly shortens the life of the equipment. Based on the analysis of the latest research, it is proposed to improve the quality and composition of water that comes from municipal water supply, artesian wells and reservoirs, before filtering and deaerating water, it is proposed to pre-treat it with hydrocavitation and a magnetic field in order to soften and change its properties. The essence of the operation of the proposed equipment is that the effect of sound hydrocavitation and a variable magnetic field on water is reduced to a single process - the splitting of water molecules in the cavitation cavity into active radicals. The essence of various processes, namely hydrocavitation and magnetic influence on the passage of chemical reactions, breaking of hydrogen bonds in water molecules, is considered. The design of the equipment for the incoming magnetic cavitation preparation of water with an additional hydrocavitation effect on water during the reciprocating movement of the liquid through the nozzle is proposed, which combines the effects of breaking hydrogen bonds in water molecules, oxidation of iron and calcium ions, increasing the Рn indicator, and after its after settling, it is fed to the ion exchange and deaeration units, and later to the heating mains.

Beam-steerable filtering patch antenna with wide-stopband suppression and stable radiation characteristics

A method of designing beam-steerable patch antennas with wide stopband suppression is proposed in this article. The wide stopband suppression characteristic is realized by designing suitable parallel coupled lines and open-circuited stubs. The beam steering characteristic is achieved by using a driven patch and two pairs of metal walls vertically placed on both sides of the driven antenna. By controlling the different states of the switching PIN diodes loaded between metal walls, the stable beam steering characteristic can be obtained over the entire operating bandwidth. An experimental antenna is designed and manufactured to validate the approach. The beam steering angles of the simulation and measurement results are ±30°. Moreover, in the three proposed operating states, the out-of-band suppression from 2.6 GHz to 10 GHz is more than 16 dB. The proposed antenna can achieve the characteristic of both wide stopband suppression and beam steering. In addition, the proposed antenna is able to maintain good impedance characteristics during beam steering and maintain stable beam over the entire operating bandwidth.

JET far-infrared interferometer/polarimeter diagnostic system—40 years of lessons learned

Originally designed for 5 years of plasma operations, the JET far infrared interferometer/polarimeter diagnostic system was still operating at full capability nearly 40 years later in ITER-relevant conditions (e.g. metal wall, tungsten divertor) for multiple D–T campaigns, albeit with significantly lower neutron fluences. The original design had to be adapted substantially over the years due to machine changes, leading to reduced signal and access to mirrors etc, and the diagnostics still worked due to the excellent dynamic range of the detectors. This paper will discuss invaluable lessons learned from designing, operating, optimising and enhancing such a complex system and how these can be used for developing a new class of laser-based diagnostics for next-generation reactor-grade machines.

Analysis of the building on the air shock wave by direct dy-namic method (with LIRA-FEM soft-ware)

Calculation of the impact of air shock waves on buildings is extremely important for our country, which is in a state of war. Studying the structural safety and survivability of load-bearing reinforced concrete structures under influence is an important task, especially for critical infrastructure facilities. A blast scenario can be carried out directly in an FEA program as a time history analysis evaluate varying levels of structural damage and to minimize loss of life.The article is devoted to the features of the calcula-tion of buildings under the influence of air shock waves using the finite element method using the LIRA-FEM software complex. The features of ex-plosive loads, typical shock wave parameters, and the order of analysis for explosive loads are taken into consideration. The primary distinctions be-tween shock or explosion impacts and regular loads are explained. In-depth consideration is given to the problems of determining shock wave parameters and how they affect structures. Also included are the techniques for evaluating structures for explosive impacts.Using LIRA-FEM software, a preliminary analysis of the explosion resistance of a one-story building with a metal frame and sheet metal wall infill is carried out. It is demonstrated how to define impulse loads from a shock wave to the side walls, roofs, rear walls, and walls facing the explosion. The article describes the peculiarities of the "Time History Analysis" system in the LIRA-FEM program for ex-plosion dynamics problems.This analysis helps in the assessment of risks in the design of protective structures, development of pro-ject solutions and conducting research in the field of explosion safety.

Dielectric Screening inside Carbon Nanotubes.

Dielectric screening plays a vital role in determining physical properties at the nanoscale and affects our ability to detect and characterize nanomaterials using optical techniques. We study how dielectric screening changes electromagnetic fields and many-body effects in nanostructures encapsulated inside carbon nanotubes. First, we show that metallic outer walls reduce the scattering intensity of the inner tube by 2 orders of magnitude compared to that of air-suspended inner tubes, in line with our local field calculations. Second, we find that the dielectric shift of the optical transition energies in the inner walls is greater when the outer tube is metallic than when it is semiconducting. The magnitude of the shift suggests that the excitons in small-diameter inner metallic tubes are thermally dissociated at room temperature if the outer tube is also metallic, and in essence, we observe band-to-band transitions in thin metallic double-walled nanotubes.

Programmable metasurfaces with high angular stability for arbitrarily-polarized obliquely-incident waves

Programmable metasurfaces show enormous potential in real-time electromagnetic (EM) manipulation and their stable responses to variable EM waves including incident angle and polarization changes are crucial for related applications. However, the demonstrated programmable metasurfaces are commonly considered in normal-incident waves with fixed polarization; how to achieve stable performance in more realistic scenarios of wide-angle and full-polarized wave incidences is still a challenge. Here, we propose and realize a wide-angle and full-polarization programmable metasurface, which can generate stabilized amplitude and phase responses at both transverse electric (TE) and transverse magnetic (TM) oblique incidences. These are achieved by introducing metallic walls around the metasurface element to reduce element coupling, which greatly improves the angular stability of its reflection responses. The mechanisms of angular insensitivity are analyzed comprehensively, and as a proof of concept, obliquely-incident beam steering, large-angle beam scanning and oblique vortex beam emitting are demonstrated on this programmable metasurface. Both the simulation and experimental results demonstrate that the programmable metasurface can operate well at both TE and TM wide-angle oblique incidences in the upper half space. Our work offers an actual route for improving the angular stability and polarization insensitivity of metasurfaces, which could push them one step closer towards more complicated applications.

Validation of the ERO2.0 code using W7-X and JET experiments and predictions for ITER operation

The paper provides an overview of recent modelling of global material erosion and deposition in the fusion devices Wendelstein 7-X (W7-X), JET and ITER using the Monte-Carlo code ERO2.0. For validating the modelling tool in a three-dimensional environment, W7-X simulations are performed to describe carbon erosion from the graphite test divertor units, which were equipped in operational phase OP 1.2 and analysed post-mortem. Synthetic spectroscopy of carbon line emission is compared with experimental results from the divertor spectrometer measurement system, showing a good agreement in the e-folding lengths in the radial intensity profiles of carbon. In the case of metallic wall materials, earlier modelling of the Be/W environment in JET and ITER is revisited and extended with an updated set of sputtering and reflection data, as well as including the mixing model for describing the Be/W dynamics in the divertor. Motivated by recent H/D/T isotope experiments in JET, limited and diverted configuration pulses are modelled, showing the expected trend of both Be and W erosion increasing with isotope mass. For the JET diverted configuration pulses, it is shown that Be migrates predominantly to the upper part of the inner divertor where it initially leads to strong W erosion. With longer exposure time, the growth of a Be deposited layer leads to a reduction of W erosion in that region. A similar trend is observed in simulations of the ITER baseline Q = 10 scenario, however with a more symmetric Be migration pattern leading to deposition also on the outer divertor.

50 GHz Four-Port Coupling-Reduced Probe Card Utilizing Pogo Pins Housed in Custom Metallic Socket.

A design for a pogo-pin probe card featuring a metallic socket is proposed to eliminate signal leakage and coupling loss in a multi-port environment. The proposed metallic pogo-pin socket includes a metal wall structure between adjacent pogo pins, ensuring complete isolation. This metal wall offers an advantage in removing coupling issues between pogo pins that can occur with typical dielectric pogo-pin sockets. The designed probe card is fabricated as a prototype and verified for its performance. Measurement results using a test through line show that coupled power is minimized, providing a low-loss transmission performance of -2.14 dB to an RF chip at 50 GHz, all within a compact size. Although the dielectric spacer used to secure the pogo pins allows for some leakage, it can maintain a low coupling performance of under -15 dB in the millimeter-wave band. The prototype probe card can deliver an RF signal to a 5G circuit with a low loss of -0.7 dB at 28 GHz and -1.9 dB at 39 GHz frequency. The designed probe card is capable of transmitting multiple RF signals to the RF system without signal distortion in a multi-port environment.

Experimental research of ECW pre-ionization and assisted startup in EAST

Experimental research on the electron cyclotron wave (ECW) pre-ionization and assisted start-up was carried out systematically for the first time in EAST tokamak, which is a superconducting device with ITER-like full metal wall. Breakdown and plasma initiation at low toroidal electric fields (<0.3 V m−1) with ECW pre-ionization and startup assistance has been demonstrated. Also, the parameter domain of breakdown is significantly extended towards higher prefill gas pressure. The effect of ECW injection timing, power, toroidal injection angle on breakdown were also investigated. Injecting ECW earlier leads to an earlier breakdown and a higher plasma current ramp rate. The electron cyclotron heating (ECH) power threshold for breakdown in EAST is approximately 0.4 MW. In the range of ECH power tested in this work, higher ECH power is advantageous for achieving earlier and faster breakdown. Furthermore, the breakdown with radial ECW injection occurs earlier compared with oblique injections (co-current and counter-current). During the ECW-assisted startup, the process of burn-through is prolonged by the higher pre-filled gas pressure even though it enhances the ease of breakdown. In addition, compared to the low hybrid wave assistance, the ECW assistance has an effect in averting the generation of runaway electrons and improving the safety of device during startup. Moreover, the ECW assistance exhibits a high tolerance to the impurity and thus ensures a high ramp rate of plasma current even with a high impurity level.

A novel laser-EMAT ultrasonic longitudinal wave resonance method for wall thickness measurement at high temperatures

In this paper we propose a novel ultrasonic longitudinal wave resonance method for measuring the thickness of metal walls using a laser-electromagnetic acoustic transducer (Laser-EMAT). The method is based on the surface constraint mechanism (SCM) of the material and is expected to be capable of accurately detecting local thinning of metal walls in a non-contact manner and at high temperatures. Based on finite element analysis of laser-EMAT ultrasonic resonance measurement of aluminum alloy thickness, we investigated the effects of such key factors as SCM, irradiation parameters of laser source, and the size of EMAT receiving coil on the accuracy of thickness measurement (resonance frequency position) and on the amplitude of the resonance wave. Both numerical simulations and experiments are conducted to demonstrate that the measurement accuracy of the proposed method is not affected by SCM, irradiation laser source parameters, and EMAT receiving coil size, and that accurate detection of stepped aluminum plates with thickness thinning from 3.0 mm to 0.5 mm is achieved. Furthermore, we were able to perform rapid detection of aluminum thin plate thickness at 500 °C temperature with an EMAT lift-off of 5.0 mm and achieved a relative experimental error as small as 3.40 %. The results obtained in this study showed that the proposed method performed well in non-contact measurement of metal thinning in harsh environment of high temperature.