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The study of propagation characteristics of the millimeter-wave vortex in magnetized plasma by using the FDTD method
Full text linkORCID 0009-0009-9605-513XIt is pointed out that the millimeter-wave vortex may contribute to an efficient method of plasma heating since it was found that the millimeter-wave vortex can propagate in magnetized plasma even in which the normal plane wave is in cut-off condition. Then, it was assumed that the vortex field was the Laguerre–Gaussian (L–G) mode which is a free-space solution, but the generation and stable propagation of the L–G mode vortex are not easy in the millimeter frequency range. On the other hand, it is known that the millimeter-wave hybrid mode of the cylindrical corrugated waveguide also has vortex properties. In this paper, we investigate the propagation characteristics of a millimeter-wave vortex of a hybrid mode of a cylindrical corrugated waveguide in the magnetized plasma by using three-dimensional numerical simulations with the finite-difference time-domain (FDTD) method. It is found that the millimeter-wave vortex of hybrid mode also can propagate in the magnetized plasma even in a condition in which the normal plane wave is in cut-off condition, and the propagation power in the plasma is highly dependent on the topological charge l.journal articl
Formation of Fine Structures in Incompressible Hall Magnetohydrodynamic Turbulence Simulations
Full text linkORCID 0000-0001-5668-6900Hall magnetohydrodynamic simulations are often carried out to study the subjects of instabilities and turbulence of space and nuclear fusion plasmas in which sub-ion-scale effects are important. Hall effects on a structure formation at a small scale in homogeneous and isotropic turbulence are reviewed together with a simple comparison to a (non-Hall) MHD turbulence simulation. A comparison between MHD and Hall MHD simulations highlights a fine structure in Hall MHD turbulence. This enhancement of the fine structures by the Hall term can be understood in relation to the whistler waves at the sub-ion scale. The generation and enhancement of fine-scale sheet, filamentary, or tubular structures do not necessarily contradict one another.journal articl
Quantum-fluid correspondence in relativistic fluids with spin: from Madelung form to gravitational coupling
Full text linkThis paper explores the quantum-fluid correspondence in a charged relativistic fluid with intrinsic spin. We begin by examining the nonrelativistic case, showing that the inclusion of spin introduces a quantum correction to the classical fluid energy. This correction, coupled with Maxwell's equations, naturally leads to the Schrödinger equation in Madelung form. Building on this foundation, we extend the formalism to a relativistic perfect fluid, identifying the system's stress-energy-momentum tensor. Our analysis reveals that the trace of the quantum correction to this tensor corresponds to the energy density of an oscillator, with its frequency determined by the vorticity of the spin motion. We then use the stress-energy-momentum tensor to establish the relationship between the Ricci scalar curvature, as dictated by the Einstein field equations, and the fluid density in a static, spherically symmetric configuration. Lastly, we generalize the Madelung transformation to compressible Navier–Stokes flows with vorticity and viscosity by developing a tailored Clebsch representation of the velocity field. This theoretical framework offers potential applications for studying fluid-like systems with internal rotational degrees of freedom, commonly encountered in astrophysical settings.journal articl
Application of a Single-Crystal CVD Diamond Detector for Fast Neutron Measurement in High Dose and Mixed Radiation Fields
Full text linkORCID 0000-0002-6250-4349This article presents the method to evaluate the fast neutron energy spectrum using the single-crystal chemical vapor deposition (CVD) diamond detector to be applicable on the radiation monitoring in advanced scientific/engineering systems usually characterized with mixed and high-dose radiation field. The pulse shape discrimination (PSD) based on the shape and the width of a pulse was applied to extract events, in which fast neutron hits at the specific depth of the single-crystal diamond. Unfolding of the measured spectrum for extracted pulses could deduce the neutron energy spectrum. Experiments using monoenergetic neutron sources demonstrated the reliable capability of this method to evaluate the neutron energy spectrum quantitatively.journal articl
A collision operator for describing dissipation in noncanonical phase space
Full text linkORCID 0000-0002-2973-0635The phase space of a noncanonical Hamiltonian system is partially inaccessible due to dynamical constraints (Casimir invariants) arising from the kernel of the Poisson tensor. When an ensemble of noncanonical Hamiltonian systems is allowed to interact, dissipative processes eventually break the phase space constraints, resulting in a thermodynamic equilibrium described by a Maxwell–Boltzmann distribution. However, the time scale required to reach Maxwell–Boltzmann statistics is often much longer than the time scale over which a given system achieves a state of thermal equilibrium. Examples include diffusion in rigid mechanical systems, as well as collisionless relaxation in magnetized plasmas and stellar systems, where the interval between binary Coulomb or gravitational collisions can be longer than the time scale over which stable structures are self-organized. Here, we focus on self-organizing phenomena over spacetime scales such that particle interactions respect the noncanonical Hamiltonian structure, but yet act to create a state of thermodynamic equilibrium. We derive a collision operator for general noncanonical Hamiltonian systems, applicable to fast, localized interactions. This collision operator depends on the interaction exchanged by colliding particles and on the Poisson tensor encoding the noncanonical phase space structure, is consistent with entropy growth and conservation of particle number and energy, preserves the interior Casimir invariants, reduces to the Landau collision operator in the limit of grazing binary Coulomb collisions in canonical phase space, and exhibits a metriplectic structure. We further show how thermodynamic equilibria depart from Maxwell–Boltzmann statistics due to the noncanonical phase space structure, and how self-organization and collisionless relaxation in magnetized plasmas and stellar systems can be described through the derived collision operator.journal articl
Diversity of Early Kilonova with the Realistic Opacities of Highly Ionized Heavy Elements
Full text linkORCID 0000-0002-0786-7307{\kappa }_{\exp }\,\sim 3\times {10}^{3}\,{\mathrm{cm}}^{2}\,{{\rm{g}}}^{-1}datase
Baseline design of laser fusion research reactor with MW class laser facility
Full text linkWe propose a sub-ignition/burning reactor which is named the Laser-fusion Subcritical Power Reactor Engineering Method (L-Supreme). The reliabilities of L-Supreme in a MW class laser facility are assessed with respect to the following points: a reactor core, a target chamber, a target delivery system, an Exhaust Detritiation System (EDS), and neutron shielding. The Japan Establishment for Power-laser Community Harvest (J-EPoCH) would be applied as a MW class laser facility. A non-cryogenic glass balloon target filled with gaseous deuterium-tritium (DT) is contained in a target capsule. A chain-type magazine system might be used for a mass supply of the target capsules. Each target capsule is delivered to the center of a reactor core at 1 Hz. A batch of 10 000 laser shots would realize 0.22 MJ fusion power. The amount of tritium per batch is 1.51 × 1012 Bq. During laser experiments, unburned tritium is evacuated and transferred into an Exhaust Detritiation System (EDS). An evacuation rate of more than 0.1 m3 s−1 is required in order to recover less than 5000 Bq m−3 of the threshold of tritium concentration within 1 h. For safety, emergency situations such as tritium leakage in facilities are examined. The EDS works by internal circulation processes. Assuming leakage of tritium for a batch, an air circulation flow rate of 4100 Nm3 h−1 is required in an experimental hall for recovering less than 5000 Bq m−3 within 48 h. A primary and secondary neutron shield concept are proposed and would provide full neutron shielding. We conclude that it is possible to construct the L-Supreme system by marshalling current technologies.journal articl
The evolutionary process of W-V mixed dumbbell in tungsten crystals: A study about W-V alloy as a plasma-facing material in fusion devices
No full textAlloying is widely used to improve the radiation resistance of plasma-facing materials. The first-principles method based on density function theory was used in this work to study the stability and mobility properties of the W-V mixed dumbbell pair. The diffusion of monovacancy and recovery of mixed dumbbell pairs were also studied. The rotations and diffusion results indicated that the W-V mixed dumbbell pair diffusions are favored in two/three-dimensional motion because of low energy barriers. And the results are also suggested the mixed dumbbell lowers the diffusion energy barriers of the monovacancy. New vacancy diffusion modes were also observed along the 〈110〉 direction during the simulation. Besides, the addition of V may also moderate the diffusion of W SIA in 〈111〉 direction.journal articl
Deep learning model for predicting the spatial distribution of binding energy from atomic configurations
Full text linkUnderstanding plasma-material interaction is crucial for achieving steady-state operation of magnetic confinement fusion devices. Kinetic Monte Carlo (kMC) simulation is a powerful tool for investigating the motion of atoms in the plasma facing materials under the influence of this interaction. To predict trapping sites and migration energies necessary for kMC simulations, we developed a deep learning model based on pix2pix for predicting the spatial distribution of binding energy. Results show that the model can reproduce spatial distributions similar to the true values. However, larger errors occur in regions with steep value gradients.journal articl
Theoretical investigation of structural, electronic, mechanical, surface work function and thermodynamic properties of La1-xMxB6 (M = Ba, Sr, Ca) compounds: Potential plasma grid materials in N-NBI system
Full text linkThis study employs first-principles calculations to investigate the structural, electronic, and mechanical properties of La1-xMxB6 (M = Ba, Sr, Ca), focusing on the surface work function, elastic constants, bulk modulus, shear modulus, Young’s modulus, Debye temperature, and melting point. The results indicate that doping generally leads to a reduction in the surface work function, with La0.375Ba0.625B6 achieving a work function as low as 1.27 eV. The influence of doping concentration on the mechanical properties and anisotropy is analyzed, revealing that La1-xMxB6 and La0.5Sr0.5B6 exhibit oscillatory changes related to the layered structure of the dopants. Brittleness is assessed through the B/G ratio and Poisson’s ratio. Thermodynamic analysis shows that the melting points of these compounds exceed 2000 K. These findings provide useful references for choosing cesium-free electrode materials applied for plasma-facing applications in neutral beam injection.journal articl