Torus Configuration Research Articles

The Workspace Analysis of the Delta Robot Using a Cross-Section Diagram Based on Zero Platform

This paper introduces a new concept of a zero-platform delta robot with three key parameters affecting the shape and size of the workspace. This concept is applied to directly bring the torus configuration into the links of the robot and shows its usefulness in configuring and generating the workspace conveniently. Analyzing the workspace of parallel robots, such as delta robots, requires extensive computation due to the constraints between the links, typically requiring complex equations or numerical methods. This paper proposes a new method for quickly estimating the shape and size of the workspace using a cross-section diagram based on a geometrical analysis of the zero-platform delta robot. The shape and size of the workspace can be rapidly estimated because the intersection of three cross-section diagrams needs only the torus’s 2D operation. Comparing the workspace between the cross-section diagram and the 3D CAD software, this paper shows that the cross-section diagram can analyze the shape and size of the workspace quickly and give a more geometrical understanding of the workspace.

Asymptotically preserving particle methods for strongly magnetized plasmas in a torus

We propose and analyze a class of particle methods for the Vlasov equation with a strong external magnetic field in a torus configuration. In this regime, the time step can be subject to stability constraints related to the smallness of Larmor radius. To avoid this limitation, our approach is based on higher-order semi-implicit numerical schemes already validated on dissipative systems [3] and for magnetic fields pointing in a fixed direction [10,11,13]. It hinges on asymptotic insights gained in [12] at the continuous level. Thus, when the magnitude of the external magnetic field is large, this scheme provides a consistent approximation of the guiding-center system taking into account curvature and variation of the magnetic field. Finally, we carry out a theoretical proof of consistency and perform several numerical experiments that establish a solid validation of the method and its underlying concepts.

Chemically Fresh Gas Inflows Detected in a Nearby High-mass Star-forming Region

Abstract We report the detection of a chemically fresh inflow that is feeding high-mass young-stellar-object (HMYSO) growth in the nearby high-mass star-forming region G352.63 made with both the Atacama Large Millimeter/submillimeter Array (ALMA) and the Submillimeter Array (SMA). High-quality images of the dust and molecular lines from both ALMA and SMA have consistently revealed a gravitationally controlled cold (∼10 K) gas inflow of chemically fresh molecules (e.g., CCH and HC3N) toward the central HMYSO and its surrounding dense gas structure, which has a possible torus- or disk-like morphology. The HMYSO is also observed to have an outflow, which is nearly perpendicular to the torus and its parental filament, and thus can be clearly separated from the inflows. These kinematic features provide observational evidence to support the conjecture that the infalling streamers in high-mass star-forming regions could proceed in a similar process to that observed in low-mass counterparts. The chemically fresh infalling streamers could also be involved in the disk or torus configuration, fragmentation, and accretion bursts that occur in both simulations and observations.

Qualification of NSTX-U Inner TF Bundle Using Hi-Fidelity Models

The National Spherical Torus eXperiment Upgrade (NSTX-U) Recovery Project provides a national facility for the study of plasma confinement, heating, and current drive in a low-aspect-ratio, spherical torus configuration. For the NSTX-U Recovery Project, key system capabilities must be achieved in order to meet operational goals. The inner toroidal field (TF) bundle is part of the center stack with 36 pie-shaped wedges (TF inner legs) bonded into a cylindrical bundle. The inner bundle is connected to outer legs via flex straps, and an ohmic heating (OH) coil is wound around the inner TF bundle, with a layer of aquapour in between acting as a winding surface between TF-OH coils. The TF bundle for the Recovery Project underwent two expert reviews to gain an improved understanding of issues identified from the extent of condition and the magnet design verification and validation review; this was to ensure confidence in the ability of the TF-OH center stack assembly to meet physics requirements for operations. A hi-fidelity, finite element model was developed with appropriate detail for multiphysics analysis of the bundle and to provide a baseline model to use as a standard against which the allowable stresses were compared. The model was also used to understand mechanical behavior and to assess implications of hypothetical delamination to the machine operation. Normal tensile stress at the bundle stub was the result of a nonuniform resistive current distribution where a relatively cold region was formed when the TF coil was pulsed. The worst case occurred at the end of the pulse when the maximum temperature gradient was established at the bundle ends. The hot spot was in compression, and the cold region was in tension. The compressive stress, which had a maximum at the bundle stub, enhanced the insulation shear capability. The in-plane torsional shear stress peaked at the end corner of the inner leg outer diameter at end of flat top. The insulation tensile and shear stresses were extracted from the hi-fidelity model using orthotropic material properties derived from first principles, and these theoretical data were verified via material tests. Load path probes were used to quantify the redistribution of torsional loads between the bundle and the external load path for a hypothetical extreme delamination condition. The extent of possible delamination was limited to regions within the radius of the flex straps. There is no significant effect on the bundle inner leg copper stress. The differential movement between the flex straps in the hypothetical extreme delamination condition is far less than the toroidal gaps between them, so there is no risk of closing these electrical gaps between the bundle turns. There is thus no impact on machine operation or even hypothetical delamination to an extreme delamination beyond the simulation-predicted delamination boundary.

Null Poynting vector electromagnetic torus

Maxwell equations in free space are solved for a standing wave torus configuration under axisymmetry, which provides a mathematical support to the microwave cavity hypothesis of ball lightning. With a null Poynting vector with the outgoing part canceling the incoming part, this torus configuration satisfies the E→//B→ gauge of the Maxwell equations.

Exact description of the boundary theory of the Kitaev toric code with open boundary conditions

In this work we consider the Kitaev Toric Code with specific open boundary conditions. Such a physical system has a highly degenerate ground state determined by the degrees of freedom localised at the boundaries. We can write down an explicit expression for the ground state of this model. Based on this, the entanglement properties of the model are studied for two types of bipartition: one, where the subsystem A is completely contained in B; and the second, where the boundary of the system is shared between A and B. In the former configuration, the entanglement entropy is the same as for the periodic boundary condition case, which means that the bulk is completely decoupled from the boundary on distances larger than the correlation length. In the latter, deviations from the torus configuration appear due to the edge states and lead to an increase of the entropy. We then determine an effective theory for the boundary of the system. In the case where we apply a small magnetic field as a perturbation the degrees of freedom on the boundary acquire a dispersion relation. The system can there be described by a Hamiltonian of the Ising type with a generic spin-exchange term.

Tomography of a simply magnetized toroidal plasma

Optical emission spectroscopy is a passive diagnostic technique, which does not perturb the plasma state. In particular, in a hydrogen plasma, Balmer-alpha (Hα) emission can be easily measured in the visible range along a line of sight from outside the plasma vessel. Other emission lines in the visible spectral range from hydrogen atoms and molecules can be exploited too, in order to gather complementary pieces of information on the plasma state. Tomography allows us to capture bi-dimensional structures. We propose to adopt an emission spectroscopy tomography for studying the transverse profiles of magnetized plasmas when Abel inversion is not exploitable. An experimental campaign was carried out at the Thorello device, a simple magnetized torus. The characteristics of the profile extraction method, which we implemented for this purpose are discussed, together with a few results concerning the plasma profiles in a simply magnetized torus configuration.

可食ロボット用全周開張式トーラス機構

This paper discusses the edible robot with expandable torus mechanism as a core configuration. The proposed torus mechanism is mainly made of gelatin. We built the prototype of the torus configuration and proposed the reflexive motion to the torus mechanism which based on the reflexive bending motion of the arm mechanism we developed at the past. From the experiment, the mechanism needs more softness and we found the needs to develop the way to keep the edible robots in the container. We are developing the edible gear, wheel, track, gripper, leg and so on in this edible robotics researches.

Design study of blanket structure based on a water-cooled solid breeder for DEMO

Blanket concept with a simplified interior for mass production has been developed using a mixed bed of Li2TiO3 and Be12Ti pebbles, coolant conditions of 15.5MPa and 290–325°C and cooling pipes without any partitions. Considering the continuity with the ITER test blanket module option of Japan and the engineering feasibility in its fabrication, our design study focused on a water-cooled solid breeding blanket using the mixed pebbles bed. Herein, we propose blanket segmentation corresponding to the shape and dimension of the blanket and routing of the coolant flow. Moreover, we estimate the overall tritium breeding ratio (TBR) with a torus configuration, based on the segmentation using three-dimensional (3D) Monte Carlo N-particle calculations. As a result, the overall TBR is 1.15. Our 3D neutronics analysis for TBR ensures that the blanket concept can achieve a self-sufficient supply of tritium.

Pure collective precession motion of a high-spin torus isomer

We investigate the precession motion of the exotic torus configuration in high-spin excited states of ${}^{40}$Ca. For this aim, we use the three-dimensional time-dependent Hartree-Fock (TDHF) method. Although the high-spin torus isomer is a unique quantum object characterized by the alignment of angular momenta of independent single-particle motions, we find that the obtained moment of inertia for rotations about an axis perpendicular to the symmetry axis is close to the rigid-body value. We also analyze the microscopic structure of the precession motion using the random-phase approximation (RPA) method for high-spin states. In the RPA calculation, the precession motion of the torus isomer is generated by coherent superposition of many one-particle--one-hole excitations across the sloping Fermi surface that strongly violates the time-reversal symmetry. By comparing results of the TDHF and the RPA calculations, we find that the precession motion obtained by the TDHF calculation is a pure collective motion well decoupled from other collective modes.

Local orbital debris flux study in the geostationary ring

A local orbital debris flux analysis is performed in the geostationary (GEO) ring to investigate how frequently near-miss events occur for each longitude slot in the GEO ring. The current resident space object (RSO) environment at GEO is evaluated, and publicly-available two-line element (TLE) data are utilized in tandem with a geostationary torus configuration to simulate near-miss events incurred by the trackable RSO population at GEO. Methodology for determining near-miss events with this formulation is introduced, and the results of the analysis for a one-year time frame are provided to illustrate the need for active GEO remediation.

Existence of an Exotic Torus Configuration in High-Spin Excited States ofCa40

We investigate the possibility of the existence of the exotic torus configuration in the high-spin excited states of (40)Ca. We here consider the spin alignments about the symmetry axis. To this end, we use a three-dimensional cranked Skyrme Hartree-Fock method and search for stable single-particle configurations. We find one stable state with the torus configuration at the total angular momentum J=60 ħ and an excitation energy of about 170 MeV in all calculations using various Skyrme interactions. The total angular momentum J=60 ħ consists of aligned 12 nucleons with the orbital angular momenta Λ=+4, +5, and +6 for spin-up or -down neutrons and protons. The obtained results strongly suggest that a macroscopic amount of circulating current breaking the time-reversal symmetry emerges in the high-spin excited state of (40)Ca.

Suprathermal ion transport in simple magnetized torus configurations

Inspired by suprathermal ion experiments in the basic plasma experiment TORPEX, the transport of suprathermal ions in ideal interchange mode turbulence is theoretically examined in the simple magnetized torus configuration. We follow ion tracer trajectories as specified by ideal interchange mode turbulence imported from a numerical simulation of drift-reduced Braginskii equations. Using the variance of displacements, σ2(t)∼tγ, we find that γ depends strongly on suprathermal ion injection energy and the relative magnitude of turbulent fluctuations. The value of γ also changes significantly as a function of time after injection, through three distinguishable phases: ballistic, interaction, and asymmetric. During the interaction phase, we find the remarkable presence of three regimes of dispersion: superdiffusive, diffusive, and subdiffusive, depending on the energy of the suprathermal ions and the amplitude of the turbulent fluctuations. We contrast these results with those from a “slab” magnetic geometry in which subdiffusion does not occur during the interaction phase. Initial results from TORPEX are consistent with data from a new synthetic diagnostic used to interpret our simulation results. The simplicity of the simple magnetized torus makes the present work of interest to analyses of more complicated contexts ranging from fusion devices to astrophysics and space plasma physics.

Neutral Beam Armor for NSTX Upgrade

The National Spherical Torus Experiment (NSTX) is a low aspect ratio, spherical torus (ST) configuration device which is located at Princeton Plasma Physics Laboratory (PPPL). This device is presently being upgraded to enhance its operations by adding a second Neutral Beamline (NBL). This change will nearly double the power available to the plasma but necessitate improvements to other design aspects of NSTX. Included in these upgrades are the relocation and upgrade of the NSTX Neutral Beam Armor to capture both sets of beamline source profiles while maintaining the same level of vacuum vessel wall protection.In order to minimize the space required to accomplish this, it has been proposed to relocate and reuse the existing armor array, improving the design so that two overlapping sets of beam profiles both fit completely. This beamline overlap could possibly cause the armor tiles to experience higher heat fluxes which translate into higher internal mechanical stresses. This would be mitigated by changing the isotropic graphite (ATJ) tiles in the overlap areas to a rugged 3D carbon-fiber composite (CFC) material, capable of handling thermally-induced stresses. Additional benefits to this recycling design proposal include opportunities to reduce project cost, increase diagnostic port access, and improve an awkward and difficult mounting scheme.

Divertor heat flux mitigation in high-performance H-mode discharges in the National Spherical Torus Experiment

Experiments conducted in high-performance 1.0 and 1.2 MA 6 MW NBI-heated H-mode discharges with a high magnetic flux expansion radiative divertor in NSTX demonstrate that significant divertor peak heat flux reduction and access to detachment may be facilitated naturally in a highly shaped spherical torus (ST) configuration. Improved plasma performance with high βt = 15–25%, a high bootstrap current fraction fBS = 45–50%, longer plasma pulses and an H-mode regime with smaller ELMs has been achieved in the strongly shaped lower single null configuration with elongation κ = 2.2–2.4 and triangularity δ = 0.7–0.8. Divertor peak heat fluxes were reduced from 6–12 to 0.5–2 MW m−2 in ELMy H-mode discharges using the inherently high magnetic flux expansion fm = 15–25 and the partial detachment of the outer strike point at several D2 injection rates. A good core confinement and pedestal characteristics were maintained, while the core carbon concentration and the associated Zeff were reduced. The partially detached divertor regime was characterized by an increase in divertor radiated power, a reduction in ion flux to the plate and a large neutral compression ratio. Spectroscopic measurements indicated the formation of a high-density, low-temperature region adjacent to the outer strike point, where substantial increases in the volume recombination rate and C II, C III emission rates were measured.

Compact DEMO, SlimCS: design progress and issues

The design progress in a compact low aspect ratio (low A) DEMO reactor, ‘SlimCS’, and its design issues are reported. The design study focused mainly on the torus configuration including the blanket, divertor, materials and maintenance scheme. For continuity with the Japanese ITER-TBM, the blanket is based on a water-cooled solid breeder blanket. For vertical stability of the elongated plasma and high beta access, the blanket is segmented into replaceable and permanent blankets and a sector-wide conducting shell is arranged inbetween these blankets. A numerical calculation indicates that fuel self-sufficiency can be satisfied when the blanket interior is ideally fabricated. An allowable heat load to the divertor plate should be 8 MW m−2 or lower, which can be a critical constraint for determining a handling power of DEMO.

Energetically resolved multiple-fluid equilibria of tokamak plasmas

In many magnetically confined fusion experiments, a significant fraction of the stored energy of the plasma resides in energetic, or non-thermal, particle populations. Despite this, most equilibrium treatments are based on MHD: a single fluid treatment which assumes a Maxwell–Boltzmann distribution function. Detailed magnetic reconstruction based on this treatment ignore the energetic complexity of the plasma and can result in model-data inconsistencies, such as thermal pressure profiles which are inconsistent with the total stored kinetic energy of the plasma. Alternatively, ad hoc corrections to the pressure profile, such as summing the energetic and thermal pressures, have poor theoretical justification. Motivated by this omission, we generalize ideal MHD one step further: we consider multiple quasi-neutral fluids, each in thermal equilibrium and each thermally insulated from each other—no population mixing occurs. Kinetically, such a model may be able to describe the ion or electron distribution function in regions of velocity phase space with a large number of particles, at the expense of more weakly populated phase space, which may have uncharacteristically high temperature and hence pressure. As magnetic equilibrium effects increase with the increase in pressure, our work constitutes an upper limit to the effect of energetic particles. When implemented into an existing solver, FLOW (Guazzotto et al 2004 Phys. Plasmas 11, 604–14), it becomes possible to qualitatively explore the impact of resolving the energetic populations on plasma equilibrium configurations in realistic geometry. Deploying the modified code, FLOW-M, on a high performance spherical torus configuration, we find that the effect of variations of the pressure, poloidal flow and toroidal flow of the energetic populations is qualitatively similar to variations in the background plasma. We also study the robustness of the equilibrium to uncertainties in the current profile and the energetic toroidal rotation or energetic pressure profile. For constant toroidal current and stored energy, the change in the poloidal flux with changes in the current profile is similar irrespective of whether the toroidal rotation or pressure was changed, indicating insensitivity to whether uncertainties lie in the pressure or toroidal rotation profiles. We conclude that to a first approximation, lumping the energetic and thermal fluids together, as is done for many equilibrium solvers, qualitatively produces correct results.

Torus configuration and materials selection on a fusion DEMO reactor, SlimCS

SlimCS is the conceptual design of a compact fusion DEMO plant assuming technologies foreseeable in 2020–2030s. For continuity of blanket technology from the Japanese ITER-TBM, the prime option of blanket is water-cooled solid breeder with Li 2TiO 3 (or Li 4SiO 4) and Be. A reduced-activation ferritic–martensitic steel (RAFM) and subcritical water are chosen as the structural material and coolant, respectively. The reactor has somewhat complex torus configuration with a sector-wide conducting plate slipped in between the replaceable (front) and permanent (back) blanket. In order to allow flexibility of maintenance in such a complex configuration, sector transport hot cell maintenance scheme is adopted. This paper describes characteristics of SlimCS with a focus on materials selection.

Two Dimensional Li Beam Imaging to Study the Magnetic Field Configuration Effects on Plasma Confinement in Spherical Tokamak CPD

Two dimensional lithium beam imaging technique has been applied in the spherical tokamak, CPD (Compact Plasma wall interaction experimental Device), to study the effects of various magnetic field configurations on RF plasma confinement topology. The performance of the lithium sheet beam is absolutely calibrated by a quartz crystal monitor. Experimental results show that plasma initiation takes place at the electron cyclotron resonance layer in a simple torus configuration and then it expands quickly to the low magnetic field side. Different magnetic field configurations critically affect the RF plasma confinement topology. A sharp lower boundary exists for the RF plasma in magnetic null configuration. Magnetic connection length plays the key role in defining plasma boundary and the critical value of connection length for plasma to exist in CPD is found to be ∼ 5-6 meter for a given pressure condition.

Design of the PROTO-SPHERA experiment and of its first step (MULTI-PINCH)

The design study of PROTO-SPHERA, a novel compact torus configuration, has been completed. It is composed of a spherical torus (ST) (with closed flux surfaces) and a force-free screw pinch (SP) (with open flux surfaces and fed by electrodes). PROTO-SPHERA is formed at spherical-tokamak-like densities (∼1019 m−3) with low voltage (∼200 V) between the electrodes. The idea of replacing the metal centrepost current (Itf) of the spherical tokamaks with the SP plasma electrode current (Ie) is aimed mainly at getting rid of the rod at the centre of the plasma configuration, which is the most critical component of spherical tokamak design. As a consequence it should be possible to decrease the aspect ratio A = R/a (R = ST major radius, a = ST minor radius) in the course of experiment and to increase the ratio between the toroidal plasma current (IST) and the plasma electrode current, IST/Ie ≫ 1. Matching two plasma configurations, i.e. an open flux-surface SP and a closed flux-surface ST, brings to life several radically new issues. The purpose of this paper is to analyse the equilibrium, the ideal MHD stability and the formations and modelling issues of such a combined magnetic confinement system. The MULTI-PINCH experimental setup, which is being assembled inside the START vacuum vessel (now in Frascati), will represent the first phase of PROTO-SPHERA: its goal is to prove the feasibility of a stable disc-shaped SP around the electrodes.