Large Toroids Research Articles

Effects of the parallel flow shear on the ITG-driven turbulent transport in tokamak plasmas

The impact of the parallel flow shear on the tokamak plasma stability and turbulent transport driven by the ion temperature gradient (ITG) modes is analyzed by means of local gyrokinetic numerical analyses. It is shown that the parallel flow shear increases the ITG growth rate in the linear regime, and induces a broadening and shift of the radial spectrum. Then, the different effects of the finite parallel shear on the ITG turbulence characteristics are deeply analyzed in the nonlinear regime. These studies highlight that a reduction of the thermal-ion turbulent heat flux is induced by a complex mechanism involving the nonlinear generation of an enhanced zonal flow activity. Indeed, the turbulent sources of the zonal flows are increased by the introduction of the finite parallel flow shear in the system, beneficially acting on the saturation level of the ITG turbulence. The study has been carried out for the Waltz standard case below the critical threshold of the destabilization of the parallel velocity gradient instability, and then generalized to a selected pulse of a recent JET scenario with substantial toroidal rotation in the edge plasma region. It is, thus, suggested that the investigated complex mechanism triggered by the finite parallel flow shear reducing the ITG turbulent heat fluxes could be complementary to the well-established perpendicular flow shear in a region with sufficiently large plasma toroidal rotation.

A Proposal for a Superconducting Space Magnet for an Antimatter Spectrometer

Future spaceborne spectrometers for astroparticle detection need high bending power therefore, the use of superconducting magnets is the sole applicable solution. Space magnets require high reliability that, in turn, requires high stability. Avoiding liquid helium cryogenics is also an attractive feature. The use of high temperature superconductors (HTS) or magnesium diboride (MgB2) combines both the requirements. The paper describes an HTS magnet operating at about 30 K that will be one of the main components of a space antimatter spectrometer. The magnet is a large toroid that will host a silicon tracker inside its internal volume and a 3D isotropic calorimeter in the center. The inner and outer diameters are 1 m and 4.3 m, respectively. The magnet mass is about 1200 kg.

Facet Engineering of Low-Cost Transitional Metal Oxides for Tunable ORR/OER Kinetics

To meet future needs for industries from personal devices to automobiles, energy storage devices are transitioning into the next-generation advanced battery systems beyond lithium ions with higher energy density. Among them, lithium-oxygen (Li-O2) battery stands out due to its highest theoretical energy density among all rechargeable ion battery systems. Yet, its application is severely disabled by the sluggish reaction kinetics during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). To address this problem, various catalysts have been developed with the most promising materials being the noble metals (Pt, etc.) and transitional metal oxides (TMOs such as CoxOy, MnxOy, etc.). While the noble metal catalysts offer superior performance in terms of improving the reaction kinetics, the high cost and environmental sensitivity prevent the large-scale application. As an alternative, TMOs are attracting more and more interest because they exhibit satisfactory catalytic performance while their cost and cycling durability are much better than that of noble metals. While most studies have focused on the development of different TMO structures, phases and compositions, few studies have reported the advancement in the crystalline facet engineering, particularly for the low-cost TMOs such as manganese oxides, and its effect on ORR/OER kinetics. In this work, beta-(β-)MnO2 crystals with either octahedron or rod-like shapes were successfully synthesized separately using a simple hydrothermal method. Combining various electron microscopic methods, the octahedron’s surface is seen to mostly occupied by MnO2-{111} facets, while rod’s surface is occupied by MnO2-{100}. As the cathode for Li-air batteries, the β-MnO2 with {111} facets and {100} facets catalyzed the formation of Li2O2 into large toroids and thin film, respectively. For the first time, we revealed that the control of crystal facets can switch the Li2O2 formation mechanism from the surface mode to the solution mode even in the low donor number TEGDME electrolyte. To further understand the formation kinetics of Li2O2, we referred to operando liquid cell transmission electron microscopy, by which a LiO2 phase was identified to function as the intermediate discharge products which significantly affect the formation of Li2O2 as the final product. Following this finding, DFT results further showed that the different catalytic properties were due to the different adsorption free energies for the LiO2 intermediate on the {111} and {100} facets of MnO2. Our findings revealed that facet-engineering of the low-cost TMO catalysts would open a new way for the design of lithium-air batteries with high stabilities and long cycle life. Figure 1

Tuning Li2O2 Formation Routes by Facet Engineering of MnO2 Cathode Catalysts

In lithium-oxygen batteries, the solubility of LiO2 intermediates in the electrolyte regulates the formation routes of the Li2O2 discharge product. High-donor-number electrolytes with a high solubility of LiO2 tend to promote the formation of Li2O2 large particles following the solution route, which eventually benefits the cell capacity and cycle life. Here, we propose that facet engineering of cathode catalysts could be another direction in tuning the formation routes of Li2O2. In this work, β-MnO2 crystals with high occupancies of {111} or {100} facets were adopted as cathode catalysts in Li-O2 batteries with a tetra(ethylene)glycol dimethyl ether electrolyte. The {111}-dominated β-MnO2 catalyzed the formation of the Li2O2 discharge product into large toroids following the solution routes, while {100}-dominated β-MnO2 facilitated the formation of Li2O2 thin films through the surface routes. Further computational studies indicate that the different formation routes of Li2O2 could be related to different adsorption energies of LiO2 on the two facets of β-MnO2. Our results demonstrate that facet engineering of cathode catalysts could be a new way to tune the formation route of Li2O2 in a low-donor-number electrolyte. We anticipate that this new finding would offer more choices for the design of lithium-oxygen batteries with high capacities and ultimately a long cycle life.

MATHEMATICAL OPTIMIZATION OF SUPERCONDUCTING MAGNETIC ENERGY STORAGE FOR WIND ENERGY SYSTEMS

Wind variability coupled with conditional changes in the level of energy consumption with respect to time has made the need for energy storage indispensable in increased penetration of wind energy. The quest for an environmentally friendly device with fast dynamic response and nearly infinite cycling has resulted in superconducting magnetic energy storage being proposed as a novel storage technology for wind energy systems. This paper builds on previous work in our lab that uses a magnesium diboirde superconducting magnetic energy storage system to address wind interruptions. Mathematical optimization was conducted to design large capacity toroid storage specifically to address sustained interruptions from wind turbines. The toroidal configuration consisting of 4 modules exhibited the highest normalized efficiency with the least superconductor requirement.

Common Envelope Shaping of Planetary Nebulae

Abstract The morphology of planetary nebulae emerging from the common envelope phase of binary star evolution is investigated. Using initial conditions based on the numerical results of hydrodynamical simulations of the common envelope phase, it was found that the shapes and sizes of the resulting nebula are very sensitive to the effective temperature of the remnant core, the mass-loss rate at the onset of the common envelope phase, and the mass ratio of the binary system. These parameters are related to the efficiency of the mass ejection after the spiral-in phase, the stellar evolutionary phase (i.e., RG, AGB, or TP-AGB), and the degree of departure from spherical symmetry in the stellar wind mass-loss process itself, respectively. It was also found that the shapes are mostly bipolar in the early phase of evolution, but that they can quickly transition to elliptical and barrel-type shapes. Solutions for nested lobes are found where the outer lobes are usually bipolar and the inner lobes are elliptical, bipolar, or barrel-type, a result due to the flow of the photo-evaporated gas from the equatorial region. Also, the lobes can be produced without the need for two distinct mass ejection events. In all the computations, the bulk of the mass is concentrated in the orbital or equatorial plane, in the form of a large toroid, which can be either neutral (early phases) or photoionized (late phases), depending of the evolutionary state of the system.

Breathable Carbon‐Free Electrode: Black TiO2 with Hierarchically Ordered Porous Structure for Stable Li–O2 Battery

AbstractThis paper introduces oxygen‐deficient black TiO2 with hierarchically ordered porous structure fabricated by a simple hydrogen reduction as a carbon‐ and binder‐free cathode, demonstrating superior energy density and stability. With the high electrical conductivity derived from oxygen vacancies or Ti3+ ions, this unique electrode features micrometer‐sized voids with mesoporous walls for the effective accommodation of Li2O2 toroid and for the rapid transport of reaction molecules without the electrode being clogged. In the highly ordered architecture, toroidal Li2O2 particles are guided to form with a regular size and separation, which induces the most of Li2O2 external surface to be directly exposed to the electrolyte. Therefore, large Li2O2 toroids (≈300 nm) grown from solution can be effectively charged by incorporating a soluble catalyst, resulting in a very small polarization (≈0.37 V). Furthermore, disordered nanoshell in black TiO2 is suggested to protect the oxygen‐deficient crystalline core, by which oxidation of Ti3+ is kinetically impeded during battery operation, leading to the enhanced electrode stability even in a highly oxidizing environment under high voltage (≈4 V).

Controlling Solution-Mediated Reaction Mechanisms of Oxygen Reduction Using Potential and Solvent for Aprotic Lithium-Oxygen Batteries.

Fundamental understanding of growth mechanisms of Li2O2 in Li-O2 cells is critical for implementing batteries with high gravimetric energies. Li2O2 growth can occur first by 1e(-) transfer to O2, forming Li(+)-O2(-) and then either chemical disproportionation of Li(+)-O2(-), or a second electron transfer to Li(+)-O2(-). We demonstrate that Li2O2 growth is governed primarily by disproportionation of Li(+)-O2(-) at low overpotential, and surface-mediated electron transfer at high overpotential. We obtain evidence supporting this trend using the rotating ring disk electrode (RRDE) technique, which shows that the fraction of oxygen reduction reaction charge attributable to soluble Li(+)-O2(-)-based intermediates increases as the discharge overpotential reduces. Electrochemical quartz crystal microbalance (EQCM) measurements of oxygen reduction support this picture, and show that the dependence of the reaction mechanism on the applied potential explains the difference in Li2O2 morphologies observed at different discharge overpotentials: formation of large (∼250 nm-1 μm) toroids, and conformal coatings (<50 nm) at higher overpotentials. These results highlight that RRDE and EQCM can be used as complementary tools to gain new insights into the role of soluble and solid reaction intermediates in the growth of reaction products in metal-O2 batteries.

Appearance of the prolate and the toroidal magnetic field dominated stars: Analytic approach

Abstract We have analyzed magnetized equilibrium states and shown a condition for the appearance of the prolate and the toroidal magnetic field-dominated stars using analytic approaches. Both observations and numerical stability analysis support that the magnetized star would have prolate and large internal toroidal magnetic fields. In this context, many investigations concerning magnetized equilibrium states have been tried to obtain the prolate and the toroidal dominant solutions, but many of them have failed to obtain such configurations. Since the Lorentz force is a cross-product of current density and magnetic field, the prolate-shaped configurations and the large toroidal magnetic fields in stars require a special relation between current density and the Lorentz force. We have analyzed simple analytical solutions and found that the prolate and the toroidal-dominant configuration require non-force-free toroidal current density that flows in the opposite direction with respect to the bulk current within the star. Such current density results in the Lorentz force which makes the stellar shape prolate. Satisfying this special relation between the current density and the Lorentz force is a key to the appearance of the prolate and the toroidal magnetic field-dominated magnetized star.

Spontaneous toroidal flow generation due to negative effective momentum diffusivity

Spontaneous structure formation, and in particular, zonal flows, is observed in a broad range of natural and engineered systems, often arising dynamically as the saturated state of a linear instability. Flows in tokamaks are known to self-organise on small scales, but large scale toroidal flows also arise even when externally applied torques are zero. This has previously been interpreted as the result of small externally imposed breaking of a symmetry. However, we show that for large enough field line pitch, a robust spontaneous symmetry breaking occurs, leading to the generation of strong toroidal flow structures; parameters are typical of Spherical Tokamak discharges with reversed shear profiles. The short wavelength dynamics are qualitatively similar to the growth of poloidal flow structures, and toroidal flow gradients nonlinearly saturate at levels where the shearing rate is comparable to linear growth rate. On long wavelengths, we measure Prandtl numbers of around zero for these systems, in conjunction with the formation of structured toroidal flows, and we show that this is consistent with a model of momentum transport where fluxes act to reinforce small flow gradients: the effective momentum diffusivity is negative. Toroidal flow structures are largely unaffected by collisional damping, so this may allow toroidal bulk flows of order the ion thermal velocity to be maintained with zero momentum input. This phenomenon also provides a mechanism for the generation of localised meso-scale structures like transport barriers.

Toroidal magnetic fields for protecting astronauts from ionizing radiation in long duration deep space missions

Among the configurations of superconducting magnet structures proposed for protecting manned spaceships or manned deep space bases from ionizing radiation, toroidal ones are the most appealing for the efficient use of the magnetic field, being most of the incoming particle directions perpendicular to the induction lines of the field. The parameters of the toroid configuration essentially depend from the shape and volume of the habitat to be protected and the level of protection to be guaranteed. Two options are considered: (1) the magnetic system forming with the habitat a unique complex (compact toroid) to be launched as one piece; (2) the magnetic system to be launched separately from the habitat and assembled around it in space (large toroid).In first option the system habitat+toroid is assumed to have a cylindrical shape, with the toroid surrounding a cylindrical habitat, and launched with its axis on the axis of the launching system. The outer diameter is limited by the diameter of the shroud, which for present and foreseeable launching systems cannot be more than 9m. The habitat is assumed to be 10m long and have a 4m diameter, leaving about 2m all around for the protecting magnetic field. The volume of the habitat results about 100m3, barely sufficient to a somewhat small crew (4–5 members) for a long duration (≅2 years) mission. Technological problems and the huge magnetic pressure exerted on the inner cylindrical conductor of the toroid limit to not more than 4T the maximum intensity of the magnetic field. With these parameters the mitigation of the dose inside the habitat due to the galactic cosmic rays (GCRs) is about 70% at minimum solar activity, while also most intense solar events cannot significantly contribute to the dose. The toroidal magnetic field can be produced by a large number of windings of the superconducting cable, arranged in cylindrical symmetry around the habitat to form continuous inner and outer cylindrical surfaces (‘continuous’ winding).In the option of separated launches for the habitat and the magnetic system, the volume of the habitat can be much larger, up to ≈300m3, i.e. a volume to be considered for a permanently manned space basis rather than for a spaceship. The toroidal field can occupy a larger volume around it, and indeed be less intense (B<3T) for obtaining the same mitigation of the radiation dose inside the habitat. Also for the separate launches option several structural arrangements can be foreseen, depending from the considered number of windings. The limit of only two huge windings is the most attractive, as it minimizes the material and could be mechanically more stable, but it could be the most difficult to be assembled in space.Main parameters for the different configurations are reported, and the plan for the development of solutions and techniques is presented.

Effect of ionic strength solution on the stability of chitosan–DNA nanoparticles

Chitosan–DNA nanoparticles employed in gene therapy protocols consist of a neutralised, stoichiometric core and a shell of the excess of chitosan which stabilises the particles against further coagulation. At low ionic strength, these nanoparticles possess a high stability; however, as the ionic strength increases, it weakens the electrostatic repulsion which can play a decisive part in the formation of highly aggregated particles. In this study, new results about the effect of ionic strength on the colloidal stability of chitosan–DNA nanoparticles were obtained by studying the interaction between chitosans of increasing molecular weights (5, 10, 16, 29, 57 and 150 kDa) and calf thymus DNA. The physicochemical properties of polyplexes were investigated by means of dynamic light scattering, static fluorescence spectroscopy, optic microscopy, transmission electronic microscopy and gel electrophoresis. After subsequent addition of salt to the nanoparticles solution, secondary aggregation increased the size of the polyplexes. The nanoparticles stability decreased drastically at the ionic strengths 150 and 500 mM, which caused the corresponding decrease in the thickness of the stabilising shell. The morphologies of chitosan/DNA nanoparticles at those ionic strengths were a mixture of large spherical aggregates, toroids and rods. The results indicated that to obtain stable chitosan–DNA nanoparticles, besides molecular weight and N/P ratio, it is quite important to control the ionic strength of the solution.

ATLAS Magnets Quench Protection, Safety and Controls System Experience

Quench detection and protection, and related safety systems are crucial for reliable and safe operation of superconducting magnet systems, in this case the very large toroids and solenoid of the ATLAS Detector at the Large Hadron Collider at CERN exhibiting a stored energy of 1.6 GJ. The PLC-based magnet control system is the main point of interaction between operators and magnets, deciding on allowed actions and low-level safety measures. Its evolution is continuous, taking into action new demands and interlocks. The magnet safety system is an in-house design, protecting the magnets from fatal errors on the systems themselves. Decisions are made based on machine in- puts and overlapping, multiple type sensors. A magnet diagnostics system continuously reads and stores magnet parameters and machine states. Since the prototyping, installation and early operation, valuable experience has been gathered. The magnet quench detection and protection circuits are designed with a twofold redundancy, and feature two physically separated safety chains. Also within a single quench protection chain a more than six fold redundancy is present in detection also using various detection principles like bridge type, differential voltage and superconducting quench detectors for use on superconducting bus links interconnecting coils. Other safety channels look at the status of magnet services like vacuum, cryogenics and electrical circuit components and guarantee proper and safe ramp down of the magnets. Here the experience gained is reported as well as the system response to various events occurred, in particular to the very few true magnet quenches and requested fast dumps. All have gone through long-term live testing on both the toroid and solenoid magnets, following which upgrade proposals are being formulated or already implemented.

DNA condensation using cationic dendrimers—morphology and supramolecular structure of formed aggregates

The control of DNA condensation, i.e. packaging or compaction, is essential for the living cell, but also important in many applications. One example is gene therapy that often utilises vehicles with the ability to condense DNA and thereby protect DNA against degradation, transport DNA across membranes (which act as barriers towards gene delivery), and regulate gene expression. This review discusses the ability of poly(amido amine) dendrimers to condense DNA molecules via attractive electrostatic interactions, which in turn leads to self-assembled structures with a rich variety of morphologies. The process of condensation is cooperative and kinetically controlled, and the structure of the aggregates strongly depends on the size and charge of the dendrimer, and the salt concentration of the aqueous solution. While globular aggregates are formed by large dendrimers, rods and toroids are formed by smaller sized dendrimers with lower total charge per molecule. The globular aggregates appear to be disordered, but the smaller dendrimers give rise to high-ordered packing of the DNA in ordered arrays according to a square or hexagonal unit cell. The high-ordered packing also indicates that the dendrimers deform while inducing the DNA to condense.

The ATLAS central solenoid

The ATLAS detector at the CERN LHC is equipped with a superconducting magnet system consisting of three large toroids and a solenoid. The 2.3 m diameter, 5.3 m long solenoid is located at the heart of the experiment where it provides a 2 T field for spectrometry of the particles emanating from the interaction of the counter-rotating beams of hadrons. As the electromagnetic calorimeter of the experiment is situated outside the solenoid, the coil must be as transparent as possible to traversing particles. The magnet, which was designed at KEK, incorporates progress in technology coming from the development of previous solenoids of this type, in particular that of a new type of reinforced superconductor addressing the requirement of transparency. Special attention has been paid to ensuring reliability and ease of operation of the magnet, through the application of sufficiently conservative guidelines for the mechanical and electrical design, stringent testing during manufacture, and a comprehensive commissioning program. This report gives an overview of the design, manufacture, test, installation and commissioning of the ATLAS central solenoid.

ATLAS Barrel Toroid Warm Structure Design and Manufacturing

The ATLAS barrel toroid magnet is a large air-core toroid that provides the magnetic field needed for the ATLAS muon spectrometer. The barrel toroid structure, named warm structure, holds the eight superconducting coils evenly positioned around the beam axis with an outer diameter of 20 m. The warm structure supports not only the coils but also muon detectors, services and access for the ATLAS experiment. The warm structure withstands about 1400 tons of weight and strong magnetic forces. Physics performance of the muon detectors, and the fact that many design aspects of the toroid and of other related sub-system of the ATLAS experiment are intertwined, impose stringent requirements on the warm structure design. Extensive finite element analyses have been carried out to achieve the final design. Manufacturing feasibilities and facilities have been taken into account. This paper gives an overview on the design and manufacturing of the ATLAS Barrel Toroid Warm Structure

Laser-induced production of large carbon-based toroids

We report on the production of large carbon-based toroids (CBTs) from fullerenes. The process involves two-step laser irradiation of a mixed fullerene target (76% C 60, 22% C 70). Transmission electron microscopy (TEM) clearly identifies toroidal-shaped structures as well as Q-shaped constructs. The typical diameters of the CBTs are ∼0.2–0.3 μm with tubular diameters of ∼50–100 nm, but toroids as wide as 0.5 μm are observed making them nanostructures on the verge of being microstructures.

Design optimisation of the ATLAS Barrel Toroid structure – the warm structure

The magnetic bending of muon tracks for the ATLAS Muon Spectrometer is provided by the large air-core toroid magnets. The Barrel Toroid structure, named the warm structure, is an open structure inside which the muon chambers are installed. The physics performance of the muon spectrometer imposes stringent requirements on the design of the warm structure. It should support the muon chambers with required precision and stability, the deformation of the structure must be minimised. At the same time, the quantities of the materials used in the structure must also be minimised. Through extensive structural analyses, the design optimisation has been achieved to fit with the physics requirements. This paper gives an overview on the design considerations of the warm structure.

Folding path in a semiflexible homopolymer chain: A Brownian dynamics simulation

We studied the kinetics of the folding transition of a semiflexible homopolymer chain, such as DNA, using a Brownian dynamics simulation. The folding product of a semiflexible chain exhibits a toroidal morphology. We show that semiflexible chains fold through various paths from coiled states to toroidal states stochastically. Some chains fold directly by winding around a ring along a chain. Others fold through rod states, which are kinetically trapped metastable states. Both in toroids and rods, sliding motions are noticeable. Large toroids are generated as the intermediate conformation first, and then they become smaller through the sliding motion.

Diameter-preserving orientations of the torus

The diameter of a directed graph is the maximum of the lengths of the shortest paths between all pairs of vertices. A directed graph is said to be tightly oriented if it has the same diameter as its undirected image graph. Our main result is tight orientations for all sufficiently large toroids, except those whose sizes in both dimensions are odd. We also prove the impossibility of tightly orienting all the toroids for which we do not present tight orientations, and we give partial results for dimensionality higher than two. © 1998 John Wiley & Sons, Inc. Networks 32: 1–11, 1998