Equilibrium Field Research Articles

JT-60SA Magnet System Status

The JT-60SA experimental device will be the world's largest superconducting tokamak when it is assembled in 2019 in Naka, Japan ( R = 3 m, a = 1.2 m). It is being constructed jointly by institutions in the EU and Japan under the Broader Approach agreement. Manufacturing of the six NbTi equilibrium field (EF) coils, which have a diameter of up to 12 m, has been completed. So far, 13 of the 18 NbTi toroidal field (TF) coils, each 7-m high and 4.5-m wide, have also been manufactured and tested at 4 K in a dedicated test facility in France. The first three of four Nb3Sn central solenoid (CS) modules have been completed, as have all of the copper in-vessel error field correction coils. Installation of the TF magnet, around the previously welded 340° tokamak vacuum vessel and its thermal shield, started at the end of 2016 and is currently underway. The TF magnet will in turn support the EF and CS coils.

Design, simulation and construction of the Taban tokamak

This paper describes the design and construction of the Taban tokamak, which is located in Amirkabir University of Technology, Tehran, Iran. The Taban tokamak was designed for plasma investigation. The design, simulation and construction of essential parts of the Taban tokamak such as the toroidal field (TF) system, ohmic heating (OH) system and equilibrium field system and their power supplies are presented. For the Taban tokamak, the toroidal magnetic coil was designed to produce a maximum field of 0.7 T at R = 0.45 m. The power supply of the TF was a 130 kJ, 0–10 kV capacitor bank. Ripples of toroidal magnetic field at the plasma edge and plasma center are 0.2% and 0.014%, respectively. For the OH system with 3 kA current, the stray field in the plasma region is less than 40 G over 80% of the plasma volume. The power supply of the OH system consists of two stages, as follows. The fast bank stage is a 120 μF, 0–5 kV capacitor that produces 2.5 kA in 400 μs and the slow bank stage is 93 mF, 600 V that can produce a maximum of 3 kA. The equilibrium system can produce uniform magnetic field at plasma volume. This system’s power supply, like the OH system, consists of two stages, so that the fast bank stage is 500 μF, 800 V and the slow bank stage is 110 mF, 200 V.

Information loss in effective field theory: Entanglement and thermal entropies

Integrating out high energy degrees of freedom to yield a low energy effective field theory leads to a loss of information with a concomitant increase in entropy. We obtain the effective field theory of a light scalar field interacting with heavy fields after tracing out the heavy degrees of freedom from the time evolved density matrix. The initial density matrix describes the light field in its ground state and the heavy fields in equilibrium at a common temperature $T$. For $T=0$, we obtain the reduced density matrix in a perturbative expansion, it reveals an emergent mixed state as a consequence of the entanglement between light and heavy fields. We obtain the effective action that determines the time evolution of the \emph{reduced} density matrix for the light field in a non-perturbative Dyson resummation of one-loop correlations of the heavy fields. The Von-Neumann \emph{entanglement entropy} associated with the reduced density matrix is obtained for the non-resonant and resonant cases in the asymptotic long time limit. In the non-resonant case the reduced density matrix displays an \emph{incipient} thermalization albeit with a wave-vector, time and coupling dependent \emph{effective temperature} as a consequence of memory of initial conditions. The entanglement entropy is time independent and is the \emph{thermal entropy} for this effective, non-equilibrium temperature. In the resonant case the light field fully \emph{thermalizes} with the heavy fields, the reduced density matrix looses memory of the initial conditions and the entanglement entropy becomes the \emph{thermal entropy} of the light field. We discuss the relation between the entanglement entropy ultraviolet divergences and renormalization.

Structure of chaotic magnetic field lines in IR-T1 tokamak due to ergodic magnetic limiter

In this paper we have studied an Ergodic Magnetic Limiter (EML) based chaotic magnetic field for transport control in the edge plasma of IR-T1 tokamak. The resonance created by the EML causes perturbation of the equilibrium field line in tokamak and as a result, the field lines are chaotic in the vicinity of the dimerized island chains. Transport barriers are formed in the chaotic field line and actually observe in tokamak with reverse magnetic shear. We used area-preserving non-twist (and twist) Poincaré maps to describe the formation of transport barriers, which are actually features of Hamiltonian systems. This transport barrier is useful in reducing radial diffusion of the field line and thus improving the plasma confinement.

Melt–Vapor Phase Diagram of the Te–S System

The values of partial pressure of saturated vapor of the constituents of the Те–S system are determined from boiling points. The boundaries of the melt–vapor phase transition at atmospheric pressure and in vacuum of 2000 and 100 Pa are calculated on the basis of partial pressures. A phase diagram that includes vapor–liquid equilibrium fields whose boundaries allow us to assess the behavior of elements upon distillation fractioning is plotted. It is established that the separation of elements is possible at the first evaporation–condensation cycle. Complications can be caused by crystallization of a sulfur solid solution in tellurium.

Broadening of the chiral critical region in a hydrodynamically expanding medium

We investigate higher cumulants of the sigma field as the chiral order parameter at the QCD phase transition. We derive a thermodynamic expression for the skewness and kurtosis from susceptibilities and use these to determine $S\sigma$ and $\kappa\sigma^2$ for the sigma field in equilibrium. In a next step, we study the behavior of these cumulants in both an equilibrated static medium and an expanding medium resembling the hydrodynamic stage of a heavy-ion collision. For the latter one, we find a significant broadening of the critical region.

Data-Driven Problems in Elasticity

We consider a new class of problems in elasticity, referred to as Data-Driven problems, defined on the space of strain-stress field pairs, or phase space. The problem consists of minimizing the distance between a given material data set and the subspace of compatible strain fields and stress fields in equilibrium. We find that the classical solutions are recovered in the case of linear elasticity. We identify conditions for convergence of Data-Driven solutions corresponding to sequences of ap- proximating material data sets. Specialization to constant material data set sequences in turn establishes an appropriate notion of relaxation. We find that relaxation within this Data-Driven framework is fundamentally different from the classical relaxation of energy functions. For instance, we show that in the Data-Driven framework the relaxation of a bistable material leads to material data sets that are not graphs.

Improved real-time dynamics from imaginary frequency lattice simulations

The computation of real-time properties, such as transport coefficients or bound state spectra of strongly interacting quantum fields in thermal equilibrium is a pressing matter. Since the sign problem prevents a direct evaluation of these quantities, lattice data needs to be analytically continued from the Euclidean domain of the simulation to Minkowski time, in general an ill-posed inverse problem. Here we report on a novel approach to improve the determination of real-time information in the form of spectral functions by setting up a simulation prescription in imaginary frequencies. By carefully distinguishing between initial conditions and quantum dynamics one obtains access to correlation functions also outside the conventional Matsubara frequencies. In particular the range between ω0 and ω1 = 2πT, which is most relevant for the inverse problem may be more highly resolved. In combination with the fact that in imaginary frequencies the kernel of the inverse problem is not an exponential but only a rational function we observe significant improvements in the reconstruction of spectral functions, demonstrated in a simple 0+1 dimensional scalar field theory toy model.

The inflaton portal to dark matter

We consider the possibility that the inflaton is part of the dark sector and interacts with the standard model through a portal interaction with a heavy complex scalar field in equilibrium with the standard model at high energies. The inflaton and dark matter are encapsulated in a single complex field and both scalar sectors are charged under different (approximate) global U(1)’s such that the dark matter, as well as the visible pseudo-scalar are taken to be relatively light, as pseudo Nambu-Goldstone bosons of the theory. The dark matter relic density is populated by Freeze-In productions through the inflaton portal. In particular, after the reheating, production of dark matter by inflaton decay is naturally suppressed thanks to Planck stringent constraints on the dark quartic coupling, therefore preserving the non thermal scenario from any initial condition tuning.

Nonlocal effective actions in semiclassical gravity: Thermal effects in stationary geometries

We compute the gravitational effective action by integrating out quantum matter fields in a weak gravitational field, using the Schwinger-Keldysh (in-in) formalism. We pay particular attention to the role of the initial quantum state in the structure of the nonlocal terms in the effective action, with an eye to nonlinear completions of the theory that may be relevant in astrophysics and cosmology. In this first paper we consider a quantum scalar field in thermal equilibrium, in a stationary gravitational field. We obtain a covariant expression for the nonlocal effective action, that can be expressed in terms of the curvature tensor, the four-velocity of the thermal bath and the local Tolman temperature. We discuss the connection between the results for ultrastatic and static metrics through conformal transformations, and the main features of the thermal corrections to the semiclassical Einstein equations.

Space–time covariance functions based on linear response theory and the turning bands method

The generation of non-separable, physically motivated covariance functions is a theme of ongoing research interest, given that only a few classes of such functions are available. We construct a non-separable space–time covariance function based on a diffusive Langevin equation. We employ ideas from statistical mechanics to express the response of an equilibrium (i.e., time independent) random field to a driving noise process by means of a linear, diffusive relaxation mechanism. The equilibrium field is assumed to follow an exponential joint probability density which is determined by a spatial local interaction model. We then use linear response theory to express the temporal evolution of the random field around the equilibrium state in terms of a Langevin equation. The latter yields an equation of motion for the space–time covariance function, which can be solved explicitly at certain limits. We use the explicit covariance model obtained in one spatial dimension and time. By means of the turning bands transform, we derive a non-separable space–time covariance function in three space dimensions and time. We investigate the mathematical properties of this space–time covariance function, and we use it to model a dataset of daily ozone concentration values from the conterminous USA.

A functional renormalization method for wave propagation in random media

We develop the exact renormalization group approach as a way to evaluate the effective speed of the propagation of a scalar wave in a medium with random inhomogeneities. We use the Martin–Siggia–Rose formalism to translate the problem into a non equilibrium field theory one, and then consider a sequence of models with a progressively lower infrared cutoff; in the limit where the cutoff is removed we recover the problem of interest. As a test of the formalism, we compute the effective dielectric constant of an homogeneous medium interspersed with randomly located, interpenetrating bubbles. A simple approximation to the renormalization group equations turns out to be equivalent to a self-consistent two-loops evaluation of the effective dielectric constant.

Design of magnet system for Keda Torus for Experiment (KTX) device

KTX, which stands for “Keda Torus for Experiment”, is a reverse field pinch (RFP) device, with main parameters between RFX and MST. It is supported by China domestic ITER-related research project. The target of KTX is to do the research work of “self-organization”of magnetic confinement plasma. It will include the dynamo and single spiral phenomena. Its magnet system includes the Toroidal Field (TF) coils, Ohmic Heating (OH) coils and Equilibrium field (EF) coils. The toroidal field coils should produce the magnetic field of 0.7T in center of plasma for the 1MA operation mode, the current of each TF coil is designed as 210kA. The power supplies and OH & PF coils are divided into three groups to reduce the voltages on each capacitor bank. Then flux swing is provided by the coils from OH 1 to OH 7, while the stray field in the plasma region is minimized by the coils from OH 8 to OH 13. The total ampere turns of OH coils is optimized as 11.6 MAT with 228 turns in total. The magnet system design is one of the major activities for KTX device design. The key engineering features and design including electromagnetic parameters and related R&D work are presented in this paper.

Status of the JT-60SA project: An overview on fabrication, assembly and future exploitation

JT-60SA is a superconducting tokamak developed under the Satellite Tokamak Programme of the Broader Approach Agreement between EU and Japan, and the Japanese national programme. It is designed to operate in the break-even conditions for long pulse duration (typically 100s), with a maximum plasma current of 5.5MA. Its scientific aim is to contribute at early realization of fusion energy, in support to the ITER project and also to future DEMO devices by addressing key engineering and physical issues for advanced plasma operation.The JT-60SA Project has shown steady progress in the last years: from the design of the main components, started in 2007 in a close collaboration between EU and Japan, continuing through the assembly in the torus hall, started in January 2013 with the delivery of the first large European component, the Cryostat Base. Since then big milestones have been achieved, like the complete winding and pre-installation of the three lower Equilibrium Field (EF) coils, the welding of a 340° of the Vacuum Vessel sectors, and the completion of most of the Toroidal Field (TF) Coils.Outside the tokamak hall, large auxiliary plant like the Cryogenic System (CS) and the Quench Protection Circuits (QPC) have been fully installed and commissioned, while the Switching Network Units (SNU) and TF and EF coils Power Supplies (SCMPS) are completing installation on site. Other components such as Cryostat Vessel, Thermal Shields, In Vessel Components and so forth are being manufactured and being delivered to Naka site for installation and commissioning.This paper gives technical progress on fabrication, installation and assembly of tokamak components and ancillary systems, as well as progress of JT-60SA Research Plan being developed jointly by EU and Japanese fusion communities.

Design, Construction, and Operation of the Compact Toroidal Hybrid

The Compact Toroidal Hybrid (CTH) is a low-aspect-ratio (), low-beta (%) torsatron with a major radius of . CTH is operable as a pure stellarator, but most research on this device is conducted with hybrid discharges in which a toroidal plasma current is driven in order to study magnetohydrodynamic instabilities and disruptions in current-carrying stellarator plasmas. The vacuum helical field of CTH is produced by a continuously wound helical coil with poloidal and toroidal periodicities of and , respectively. The maximum on-axis toroid al magnetic field is . The helical coil encloses a circular vacuum vessel of major radius = 0.75 m with a circular cross section of minor radius 0.29 m. A toroidal plasma current up to 80 kA is produced with an ohmic heating (OH) transformer. The average plasma radius is typically 0.20 m. Five independently controllable magnet coil sets produce the base stellarator magnetic field configuration. With 15-kW electro.n cyclotron heating at the fundamental frequency, densities of and electron temperatures of 20 eV are achieved. With the addition of OH, densities reach with temperatures of . Ten motor/generator power supplies provide up to 10 MW of power to energize the magnet set providing the equilibrium field, and a capacitor bank provides the pulsed current for the OH system. Design considerations, constraints, and construction techniques of the CTH magnet coils, vacuum vessel, and support structure are discussed, and an operational overview is given.

Design of a Feedback Control System for Keda Torus Experiment Equilibrium Field Power Supply

An equilibrium field (EQ) power supply (PS) circuit using a feedback H-bridge pulse-width-modulation controller has been developed to control the plasma horizontal position and to satisfy the requirement of plasma equilibrium in the Keda Torus eXperiment (KTX) reversed field pinch. Results from simulations of plasma discharge aimed at achieving plasma equilibrium demonstrate the success of the PS circuit design. Additionally, this design provides a feasible control solution for achieving equilibrium conditions in future KTX PS upgrades. The details of the EQ model and simulations of the poloidal field circuit are presented and discussed in this technical note.

Topological transformation of phase diagrams in KBr–оxyethylated surfactant–water pseudo-ternary systems

A scheme was developed to explain the transformation of phase diagrams for KBr–oxyethylated surfactant–water systems in response to varying temperature. This scheme was shown to correspond with the respective scheme for salt–binary solvent systems. The surfactant structure was shown to have an effect on the temperature ranges of existence of a liquid–liquid two-phase equilibrium field and the positions of critical points. The elucidated trends serve as the basis for selecting components and optimizing parameters of surfactant- involving extraction processes.

Melt–gas phase equilibria and state diagrams of the selenium–tellurium system

The partial pressures of saturated vapor of the components in the Se–Te system are determined and presented in the form of temperature–concentration dependences from which the boundaries of the melt–gas phase transition are calculated at atmospheric pressure and vacuums of 2000 and 100 Pa. The existence of azeotropic mixtures is revealed. It is found that the points of inseparably boiling melts correspond to 7.5 at % of Se and 995°C at 101325 Pa, 10.9 at % at 673°C and 19.5 at % at 522°C in vacuums of 2000 and 100 Pa, respectively. A complete state diagram is constructed, including the fields of gas-liquid equilibria at atmospheric and low pressures, the boundaries of which allow us to assess the behavior of selenium and tellurium upon distillation fractionation.

Path-integral formula for local thermal equilibrium

We develop a complete path-integral formulation of relativistic quantum fields in local thermal equilibrium, which brings about the emergence of thermally induced curved spacetime. The resulting action is shown to have full diffeomorphism invariance and gauge invariance in thermal spacetime with imaginary-time independent backgrounds. This leads to the notable symmetry properties of emergent thermal spacetime: Kaluza–Klein gauge symmetry, spatial diffeomorphism symmetry, and gauge symmetry. A thermodynamic potential in local thermal equilibrium, or the so-called Massieu–Planck functional, is identified as a generating functional for conserved currents such as the energy–momentum tensor and the electric current.

A Thermodynamic Study of a Constitutional Diagram for Duplex Stainless Steels

Arc welding involves joining two metal plates by a welding pool, which is kept molten for short periods due to an electric arc. This weld metal has, sometimes, a different composition from the plates, due to a filler metal. Arc welding is a non-equilibrium process. Technological approach, nevertheless, uses empirical tools to predict important features of the joints. In stainless steel welding, the Schaeffler diagram, and other constitutive diagrams, as the WRC 1992 diagram, are used to predict the resultant microstructure in the welded joint. The composition input is calculated by Chromium and Nickel equivalents expressions. Schaeffler diagram is used to evaluate weldability of stainless steels. Some people adapt the W and N alloying elements in Schaeffler diagram to predict the weldability of duplex stainless steels (DSS). Present work shows how these technological tools can be understood as results of phase equilibrium in key isotherms of the Fe-Cr-Ni system, used in all constitutive diagrams. The validity and limitation of the Chromium and Nickel equivalents expressions were discussed based on the effect of up to two alloying components (X1 = Mo or W and X2 = N) on the alpha/gamma phase equilibrium, as estimated by calculations in system Fe-Cr-Ni-X1-X2 that are typical DSS alloying elements. This allows extending these Chromium and Nickel equivalents expressions based on thermodynamics and to identify vulnerabilities for two important problems in DSS welding: Chromium nitride and sigma phase precipitation. Originally, Schaeffler’s diagram does not consider the effect of W and N in the (γ/α + γ) equilibrium field.