Toroidal System Research Articles

Divertor Tokamak Test facility project: status of design and implementation

Abstract An overview is presented of the progress since 2021 in the construction and scientific programme preparation of the Divertor Tokamak Test (DTT) facility. Licensing for building construction has been granted at the end of 2021. Licensing for Cat. A radiologic source has been also granted in 2022. The construction of the toroidal field magnet system is progressing. The prototype of the 170GHz gyrotron has been produced and it is now under test on the FALCON facility. The design of the vacuum vessel, the poloidal field coils and the civil infrastructures has been completed. The shape of the first DTT divertor has been agreed with EUROfusion to test different plasma and exhaust scenarios: single null, double null, XD divertor and negative triangularity plasmas. A detailed research plan is being elaborated with the involvement of the EUROfusion laboratories.

Design and development of FPGA based trigger system for automation of metallic tokamak (MT-I)

A field-programmable gate array (FPGA)-based trigger system (FTS) is designed and developed to replace the existing microcontroller-based system for the automation of metallic tokamak (MT-I). MT-I consists of three main systems: MT-I vacuum vessel and gas filling system, a pulsed power supply system, an electronic system based on diagnostics and data acquisition (DAQ) systems. The power supply system provides pulsed power input to the central solenoid (CS), poloidal field coils (PF), toroidal field coils (TF), and microwave systems using thyristors and insulated-gate bipolar transistors (IGBTs). The (DAQ) system acquires experimental data from MT-I diagnostics using national instruments (NI) DAQ cards. A concurrent processing system is required to incorporate time delay in the triggering process of central solenoid (CS), poloidal field coils (PF), toroidal field coils (TF), microwave source and DAQ systems. Therefore, an FTS is designed and developed to complement the processing capability, unlike a microcontroller. The FTS has twenty concurrent triggering channels, adjustable from time reference zero, and control from a simple graphical user interface (GUI) designed on LabVIEW. For current buffering and optical isolation against high voltages in the MT-I power supply system, a peripheral electronic system (PES) and field trigger modules (FTM) have been developed as part of FTS. The designed and developed FTS was tested successfully on MT-I.

Production of 5-fluorouracil-loaded PLGA nanoparticles with toroidal microfluidic system and optimization of process variables by design of experiments

In recent decades, microfluidics has presented new opportunities for the production of nanoparticles (NPs). However, to achieve rapid clinical translation, the production of PLGA NPs in a single microfluidic channel for both the pharmaceutical research and industry without the need for scaling is still limited. The aim of this study was to accomplish the production of reproducible and stable 5-FU loaded Poly(lactic-co-glycolic acid) (PLGA) NPs, using an innovative toroidal microfluidic system, for cancer therapy. The toroidal microfluidic system enabled the production of spherical NPs ranging from 100 to 150 nm by adjusting both the TFR within the range of 5–15 mL/min and FRR between 1:3 and 1:7. A systematic assessment of critical process variables (total flow rate; TFR, flow rate ratio; FRR) for the production of PLGA NPs was conducted using Design of Experiment (DoE). The NPs, which exhibit a uniform size distribution, remained stable even after centrifugation and storage for 3 months at 4 °C. The encapsulation efficiency of drug and the concentration of NPs were not affected by changing process parameters. The effective 5-FU encapsulation into NPs resulted in a controlled in vitro drug release. Due to the controlled release profile of the 5-FU loaded PLGA NPs, the formulation was a promising candidate for mitigating the toxic side effects of free 5-FU and improving cancer treatment. In conclusion, toroidal microfluidic system enables high-volume production of stable PLGA NPs, both with and without 5-FU.

An innovative coil fabrication and assembly process for the VNS tokamak based on in-situ winding

The paper introduces a new approach to assemble tokamak machines applied to the plasma-based Volumetric Neutron Source (VNS) device, addressing challenges related to machine topology. The VNS, designed as a compact tokamak, serves as a qualification testbed for in-vessel fusion components, especially the breeding blanket. The project aims to bridge the technology gap between ITER and DEMO. The machine size has been minimized to maximize the Neutron Wall Load (NWL). This results in a small, dense plasma and, due to the massive neutron shielding structure, a comparably large distance between the plasma and the equilibrium magnets, challenging the primary stabilization and shaping of the plasma. To overcome this, a magnet system architecture is proposed for VNS in which the poloidal field (PF) coil system is placed inside the TF coils. An assembly procedure is proposed, where the superconducting PF coils are first completed and positioned around the vacuum vessel, followed by the in-situ winding and assembly of the toroidal field coil system. The main magnetic cage components of the machine are based on High-Temperature Superconductors (HTS) to avoid the need for heat treatment. The paper presents the advantages of the magnet system architecture, and the preliminary feasibility study of the machine assembly process.

Mechanism analysis of the vortex ring and its effects on an axial descending rotor

A vortex ring is a flow phenomenon involving a complex toroidal vortex system. When a rotor is in descending flight, it may enter the vortex ring state (VRS), which will affect the rotor’s aerodynamic characteristics and even endanger it. In this paper, to clarify the aerodynamic mechanism by which the vortex ring exerts its effects on an axial descending rotor, an unsteady numerical simulation method for the rotor integrated with structured moving overset grids is proposed and validated using experimental data. This numerical simulation method is then applied to analyze the aerodynamic characteristics of the rotor in descending flight. The variations of the aerodynamic forces and the flow characteristics in the slipstream are analyzed to elucidate the physical mechanisms responsible for the relationships between the aerodynamic loads, flow field, and vortices when the rotor is in the VRS. The effects of the VRS cause a sharp drop in the average aerodynamic forces, which directly affects the safety and reliability of a rotor aircraft. In the slipstream of the descending rotor, a distinct vortex ring forms and moves upward as the velocity of descent increases. The most severe VRS occurs at a nondimensional velocity of descent of 1.13 when the center of the highly unsteady vortex ring is right at the blade tip, and this can be used as an indicator of the VRS. The physical mechanism by which the VRS exerts its effects can be attributed to the low pressure induced by strong vortices. The VRS decreases the pressure on the lower surface of the blade and increases the pressure on the upper surface, resulting in a reduction in the aerodynamic loads. In comparison with the hovering state, the VRS results in a much larger vortex strength and possesses a different vortex structure.

System Engineering based on Remarkable Geometric Properties of Space

In this paper, we regard designing systems based on remarkable geometric properties of space, namely valuable rotational symmetry and asymmetry harmonious, using schematic and diagrammatic presentations of the systems. Moreover, the relationships are a way to comprehend original information to serve as a source of research and designing the systems. The objective of the future methodology is the advanced study of spatial geometric harmony as profiting information for expansion fundamental and applied researches for optimal solutions of technological problems in systems engineering. These systems engineering designs make it possible to improve the quality indices of devices or systems concerning performance reliability, code immunity, and the other operating indices of the systems. As examples, both up to 25% errors of lengths correcting code and high-speed self-error-correcting vector data code formed under a toroidal coordinate system are presented.

Development of a toroidal soft x-ray imaging system and application for investigating three-dimensional plasma on J-TEXT

A toroidal soft x-ray imaging (T-SXRI) system has been developed to investigate three-dimensional (3D) plasma physics on J-TEXT. This T-SXRI system consists of three sets of SXR arrays. Two sets are newly developed and located on the vacuum chamber wall at toroidal positions of ° and °, respectively, while one set was established previously at °. Each set of SXR arrays consists of three arrays viewing the plasma poloidally, and hence can be used separately to obtain SXR images via the tomographic method. The sawtooth precursor oscillations are measured by T-SXRI, and the corresponding images of perturbative SXR signals are successfully reconstructed at these three toroidal positions, hence providing measurement of the 3D structure of precursor oscillations. The observed 3D structure is consistent with the helical structure of the m/n = 1/1 mode. The experimental observation confirms that the T-SXRI system is able to observe 3D structures in the J-TEXT plasma.

Vertical stray field measurements using an electron beam in the MEPhIST-0 tokamak

In the MEPhIST-0 tokamak, toroidal magnetic coil system is implemented as a single continuous toroidal solenoid. This design ensures synchronized operation of each segment of the solenoid and requires only one power supply line to operate. However, this configuration has the downside of introducing stray vertical and radial magnetic field components, which result from the inclination of the solenoid segments. Such stray fields can be measured using an electron beam, as previously demonstrated in experiments on T-15, TEXTOR, KSTAR, and SST-1. This paper describes the parameters of the experiment and presents the main results obtained from the MEPhIST-0 tokamak. Two experimental techniques for measuring the vertical magnetic field are discussed: one with a change in the current direction in the toroidal solenoid and one without. The ratio of the stray vertical field to the toroidal field was found to be approximately 0.5%. The conducted experiments highlight the necessity of compensating for the stray vertical field using additional poloidal coils.

CFD investigation of fluid and heat transfer in a single-phase natural circulation toroidal loop

Natural circulation occurs due to a temperature-induced density gradient, typically observed within closed loops where the fluid is heated in the upper section and cooled in the lower section. This phenomenon finds numerous engineering applications, particularly as a passive heat removal mechanism in nuclear reactors, significantly enhancing their safety. However, the computational modeling of natural circulation poses challenges due to its complex, multidimensional, and nonlinear characteristics. Furthermore, in such systems, fluid dynamics and thermal aspects are intricately intertwined. Hence, the objective of this study is to evaluate the fluid and thermal behavior of a toroidal loop under natural circulation using the Computational Fluid Dynamics (CFD) ANSYS CFX package. A 2D model is employed, along with the Boussinesq approximations, as they are well-suited for toroidal systems. Turbulence is calculated using the k−ϵ. Various modified Grashof Numbers (Gr) normalized by the geometric parameter (NG) are utilized, ranging from 5.4×103 to 4.7×105, for two different Prandtl numbers. The lowest Grm/NG value in each simulation represents the convection lower limit (flow initiation), while the highest value indicates the convergence limit, beyond which a steady state cannot be achieved. Temperature and velocity profiles are presented, and their variations with the power level are discussed. The resulting Reynolds of Steady State (Ress) are plotted against Grm/NG values, demonstrating good agreement with experimental data. As the Prandtl Number increases, the system is observed to enter an unstable zone at an earlier stage. Finally, it is observed that multiple steady states exist for Pr=0.7, and their implications are discussed.

Absorption of Microwaves During Plasma Heating at the Second Harmonic of Electron Cyclotron Resonance in Tokamaks and Stellarators: Linear Theory and Experiment

We study the microwave absorption during electron cyclotron resonance heating (ECRH) by the extraordinary wave at second harmonic (X2 mode) in the T-10 tokamak and TJ-II stellarator in a wide range of plasma densities, and compare experiments with the classical formulas for the absorption of the injected ECR power. Empirical relations for the absorption efficiency and for the critical plasma density {{n}_{{{text{cr}}}}}, which separates the regions with full and partial absorption of the injected ECR power, are obtained using the numerical simulation of the heat transport with the transport model of canonical profiles. It is shown that in both devices, the range of densities exists, where the absorption predicted by the classical formulas is almost full, while according with the empirical formula, only a small fraction of the power is absorbed. The obtained relations allow ones to optimize the conditions of ECRH in toroidal systems for magnetic plasma confinement.

Design and Development of 0.3-T Toroidal Field Coil System for Small-Sized MT-II Spherical Tokamak

The achievement of a high toroidal magnetic field in a small spherical tokamak is challenging because of the small bore area in the central cylinder of the vacuum vessel. In this paper, we present a toroidal field coil of 0.3 T at the center of the MT-II tokamak. It has been designed, developed, and tested for installation at Pakistan Tokamak Plasma Research Institute (PTPRI). The coil is made of highly pure oxygen-free copper. It has a cross-sectional area of 10 × 15 mm2 (150 mm2) for the flow of an approximately 20-kA current to produce a 0.33 T toroidal magnetic field at the center of the tokamak. Mechanical support for the central stack of the inner legs is provided by a twisted grooved nylon cylinder to control the torque and attractive forces. The repulsive force density between the joints of the outer and inner legs is balanced by nuts and bolts along with an insulated ring of Teflon and an isolated metallic clamp from both ends. This compressive force also reduces connection resistance. The simulated currents and magnetic field are confirmed from the experimental results as well.

The MAgnet Design Explorer algorithm (MADE) for LTS, Hybrid or HTS toroidal and poloidal systems of a tokamak with a view to DEMO

The European Roadmap to Fusion Electricity (Federici et al., 2018) [1] details the path to complete within the next three decades the DEMOnstration power plant, DEMO, aiming to a net gain of Energy Q=40. The 2018 DEMO baseline considers a 2 GW tokamak device, a target performance of 6 T on the plasma, with a major radius of 9 m. Considering the plasma aspect ratio and elongation, and the radial build of the thermal shield, the outer radius of the TFC inner leg is about 4.3 m. In the current designs, the TFC winding pack operates in a range of B = 12−13 T and is based on low temperature superconductors (LTS). As an alternative, High Temperature Superconductors (HTS) could be employed to extend the coil operation beyond the typical J/T/B range of Nb3Sn. The rationale behind the exploration of a fully HTS or Hybrid HTS/LTS design of the TFC Winding Pack (WP) is twofold: on the one hand, it is possible to maintain the target performance of the machine redesigning the radial build of each magnet as a function of a more efficient cable in terms of critical current density; on the other hand, it is possible to keep the machine power constant, increasing the field on the plasma axis, and consequently define a new radial build.This work presents and describes a combined algorithm implemented to enhance the DEMO magnet systems and optimize the DTT central solenoid, capable of accounting for the main electromagnetic and structural constraints, and consistently reshape the machine.

Design and Optimization of Multimodule IPPS System With Toroidal Structure

The cooperative work of multiple modules is an important technical stage in the practical process of inductive pulsed power supply (IPPS). This article proposes a novel configuration of multimodule system, in which the inductors of each module are arranged in a toroidal way. This configuration can greatly improve the energy storage by utilizing the mutual inductance between modules, and the electromagnetic interference can also be reduced. Based on the circuit analysis and formula derivation, the decoupling equivalent greatly simplifies the calculation of system performance. The genetic algorithm (GA) is used for the parametric design of the 2 MJ toroidal IPPS system, and one of the solutions achieves an output current of 361 kA and an energy density of 6.21 MJ/m3. In addition, the three configurations of multimodule IPPS system are compared, and it is found that the proposed toroidal scheme can achieve higher indicators.

Failure analysis of a heavy gauge fastener of the ITER toroidal field gravity support system

The Gravity Supports (GS) of the ITER Toroidal Field (TF) coils are positioned at the bottom of the machine and are situated under the 18 toroidal field coils. Each support includes 26 high strength bolts with M60 and M85 gauge. The TFGS will sustain a total load of about 11,000 tonnes of dead weight of the magnet system. Moreover, they will be exposed in operation to large electromagnetic forces and possible seismic dynamic loads. The bolts are manufactured from forged rods of double aged UNS N07718 (also known as Inconel® 718), a high strength nickel base superalloy. Stringent material specification and quality controls requirements apply to the threaded bolts and the other components of the GS. A complete break of one M85 bolt was discovered, that occurred about 40 days after its installation and preloading, prior to the application of any operating stress. Half of the part blew out from the bolthole and was found lying horizontally on the GS top area. Following the incident, a comprehensive failure analysis was carried out, based on a combination of non-destructive and destructive examinations including advanced techniques such as computed microtomography, immersion ultrasonic testing (UT) and fracture mechanics. The delayed rupture was understood as due to a combination of cavities not closed by the forging operations associated to a continuous network of brittle secondary phases at the grain boundaries, resulting in a local lack of ductility, poor impact toughness and mechanical properties locally lower than specified. As a consequence of the incident, UT procedures were developed to confirm that the remaining bolts, including the installed ones, are free of cavities using sufficiently conservative criteria and fit for purpose prior to operation. In particular, in-situ axial inspections allowed installed bolts that could contain relevant imperfections to be identified and replaced.

Experimental study of plasma gun-assisted field-reversed configuration formation

The field-reversed configuration (FRC) is a compact toroidal plasma system related to the research of alternative fusion reactors. Improving the FRC formation, which is critical to the improvement of its overall quality, is reported in this paper by using a plasma gun to assist the pre-ionization process. For the single-translated FRC, the poloidal magnetic flux increases around 30%, accompanied by an increase in the separatrix radius and plasma density, while its translation speed is found to decrease slightly. The estimated increase in particle inventory is more than 60%. The improvement of these parameters also extends the lifetime of the FRC.

High-resolution x-ray monochromatic imaging for laser plasma diagnostics based on toroidal crystal

Monochromatic x-ray imaging is an essential method for plasma diagnostics related to density information. Large-field high-resolution monochromatic imaging of a He-like iron (Fe XXV) K α characteristic line (6.701 keV) for laser plasma diagnostics was achieved using a developed toroidal crystal x-ray imager. A high-index crystal orientation Ge 〈531〉 wafer with a Bragg angle of 75.37° and the toroidal substrate were selected to obtain sufficient diffraction efficiency and compensate for astigmatism under oblique incidence. A precise offline assembly method of the toroidal crystal imager based on energy substitution was proposed, and a spatial resolution of 3–7 μm was obtained by toroidal crystal imaging of a 600 line-pairs/inch Au grid within an object field of view larger than 1.0 mm. The toroidal crystal x-ray imager has been successfully tested via side-on backlight imaging experiments of the sinusoidal modulation target and a 1000 line-pairs/inch Au grid with a linewidth of 5 μm using an online alignment method based on dual positioning balls to indicate the target and backlighter. This paper describes the optical design, adjustment method, and experimental results of a toroidal crystal system in a laboratory and laser facility.

Conductor Design for Toroidal Field Coils of a High Magnetic Field Tokamak TRT20

Recently, the developmentof the concept project of the high magnetic field (HMF) tokamak continues in the Russian Federation. The value of the magnetic field on the plasma axis in the device is about 8 T. The maximum field on the winding of the toroidal field coils is about 15 T. The creation of a high magnetic field in a limited space of tokamak-type device with a given aspect ratio-R/a≈3.77 (R = 2.15 m-the big radius of the tokamak, and a = 0.57-the “radius” of the plasma) leads to a significant increase in the engineering current density in the toroidal field coils. The mechanical stresses in the magnet increase accordingly. Acceptable from a technical point of view for protective energy output are the values of the maximum electrical voltage relative to the ground-U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ≤+/−5 kV and the temperature in the “hot spot” - T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ∼200 K. In addition, it is necessary to minimize heat losses in the stationary mode of operation of the tokamak, which significantly depend on the number of current leads used in the toroidal magnet. In this paper, we propose original possible solutions of the problems listed above. A “cable-in-conduit” type of conductor (CICC) is used in the TRT toroidal magnetic system. The cable portion of the conductor is manufactured from parallel non-transposed tapes of HTS REBCO coated conductor, which are oriented mainly parallel to the vector of the toroidal magnetic field. We call this design PaST (Parallel Stacked Tapes) conductors. The design of the conductor is developed to the requirements for a real device and differs from the previously proposed by more compact dimensions.

A high-Q superconducting toroidal medium frequency detection system with a capacitively adjustable frequency range >180 kHz.

We describe a newly developed polytetrafluoroethylene/copper capacitor driven by a cryogenic piezoelectric slip-stick stage and demonstrate with the chosen layout cryogenic capacitance tuning of ≈60 pF at ≈10 pF background capacitance. Connected to a highly sensitive superconducting toroidal LC circuit, we demonstrate tuning of the resonant frequency between 345 and 685kHz, at quality factors Q > 100 000. Connected to a cryogenic ultra low noise amplifier, a frequency tuning range between 520 and 710kHz is reached, while quality factors Q > 86 000 are achieved. This new device can be used as a versatile image current detector in high-precision Penning-trap experiments or as an LC-circuit-based haloscope detector to search for the conversion of axion-like dark matter to radio-frequency photons. This new development increases the sensitive detection bandwidth of our axion haloscope by a factor of ≈1000.

The GBS code for the self-consistent simulation of plasma turbulence and kinetic neutral dynamics in the tokamak boundary

A new version of GBS (Ricci et al. (2012) [27]; Halpern et al. J. Comput. Phys. 315 (2016) 388-408; Paruta et al. (2018) [11]) is described. GBS is a three-dimensional, flux-driven, global, two-fluid turbulence code developed for the self-consistent simulation of plasma turbulence and kinetic neutral dynamics in the tokamak boundary. In the new version presented here, the simulation domain is extended to encompass the whole plasma volume, avoiding an artificial boundary with the core, hence retaining the core-edge-SOL interplay. A toroidal coordinate system is introduced to increase the code flexibility, allowing for the simulation of arbitrary magnetic configurations (e.g. single-null, double-null and snowflake configurations), which can also be the result of the equilibrium reconstruction of an experimental discharge. The implementation of a new iterative solver for the Poisson and Ampère equations is presented, leading to a remarkable speed-up of the code with respect to the use of direct solvers, therefore allowing for efficient electromagnetic simulations that avoid the use of the Boussinesq approximation. The self-consistent kinetic neutral model, initially developed for limited configurations, is ported to the magnetic configurations considered by the present version of GBS and carefully optimized. A new MPI parallelisation is implemented to evolve the plasma and neutral models in parallel, thus improving the code scalability. The numerical implementation of the plasma and neutral models is verified by means of the method of manufactured solutions. As an example of the simulation capabilities of the new version of GBS, a simulation of a TCV tokamak discharge is presented.

Entropy generation for MHD two phase blood flow through a curved permeable artery having variable viscosity with heat and mass transfer

Present study deals with the analysis of entropy generation of MHD blood flow through a stenosed permeable curved artery with heat source and chemical reaction. Blood flow is considered in two-phases; core and plasma region, respectively. Viscosity of the core region is considered as temperature-dependent, while constant viscosity is considered in plasma region. The governing equations of the proposed two-phase blood flow model are considered in the toroidal coordinate system. The second-order finite difference method is adopted to solve governing equations with 10−6 tolerance in the iteration process. A comparative study of darcy number (Da) is performed to understand the influence of permeable and impermeable wall conditions. The effect of various physical parameters such as magnetic field (M), viscosity variation parameter (λ1), Darcy number (Da), Brinkman number (Br), heat source (H), chemical reaction parameter (ξ) etc. are displayed graphically on the flow velocity, temperature, concentration, wall shear stress (WSS), frictional resistance profile and entropy generation profiles. A comparison with published work has also been displayed through the graph to validate the present model, and it is in fair agreement with the existing work. The present study suggested that the curvature and permeability of the arterial wall raise the risk of atherosclerosis formation, while the implication of heat source on the blood flow lower this risk. Clinical researchers and biologists can use the current mathematical research to lower the risk of lipid deposition and predict the risk of cardiovascular disease, and then diagnose patients based on risk.