Tomokazu Kato

Bio: Tomokazu Kato is an academic researcher from Waseda University. The author has contributed to research in topics: Plasma & Electric field. The author has an hindex of 8, co-authored 41 publications receiving 228 citations.

On the Viscoelasticity and Complex Dielectric Constant in the Presence of an Electric Field and a Shearing Laminar Flow in Solution of Macromolecules

Abstract: The effect of an electric field on the intrinsic viscoelasticity and the effect of shearing laminar flow on the dielectric properties of dilute solutions are calculated, based on the model of a spheroidal macromolecule with dipole moment along its symmetry axis. It is shown that the intrinsic viscosity increases proportionally to the square of the applied electric field and the dielectric constant increases proportionally to the square of the velocity gradient. Simple thermodynamical considerations are given.

Stochastic acceleration by intense laser fields

Abstract: A stochastic acceleration mechanism which is a direct acceleration mechanism effective for the intense laser case is studied by the Fokker–Planck approach. The Fokker–Planck equation of the electron distribution function is derived from the equation of motion of electrons which interact with filamented laser fields. The Fokker–Planck equation contains nonlinear coefficients and gives an anisotropic distribution in momentum space. The strong directionality of the acceleration is explained. The accelerated electrons tend to be collimated towards the direction of the wave vector. The effective temperature scales as T∝tβ with β≃1.

Simulations of diocotron instability using a special-purpose computer, MDGRAPE-2

Abstract: The diocotron instability in a low-density non-neutral electron plasma is examined via numerical simulations. For the simulations, a current-vortex filament model and a special-purpose computer, MDGRAPE-2 are used. In the previous work, a simulation method based on the current-vortex filament model, which is called “current-vortex method,” is developed. It is assumed that electric current and vorticity have discontinuous filamentary distributions, and both point electric current and point vortex are confined in a filament, which is called “current-vortex filament.” In this paper, the current-vortex method with no electric current is applied to simulations of the non-neutral electron plasma. This is equivalent to the traditional point-vortex method. MDGRAPE-2 was originally designed for molecular dynamics simulations. It accelerates calculations of the Coulomb interactions, the van der Waals interactions and so on. It can also be used to accelerate calculations of the Biot–Savart integral. The diocotron modes reproduced by the simulations agree with the result predicted by linear theory. This indicates that the current-vortex method is applicable to problems of the non-neutral plasma. The linear growth rates of the diocotron instability in the simulations also agree with the theoretical ones. This implies that MDGRAPE-2 gives the sufficiently accurate results for the calculations of the current-vortex method. A mechanism of merging of electron clumps is demonstrated by the simulations. It is concluded that the electric field induced by the conducting wall makes the nonlinear stage unstable and causes the clumps to merge.

New method for calculating the one-particle green's function with application to the electron-gas problem

Abstract: A set of successively more accurate self-consistent equations for the one-electron Green's function have been derived. They correspond to an expansion in a screened potential rather than the bare Coulomb potential. The first equation is adequate for many purposes. Each equation follows from the demand that a corresponding expression for the total energy be stationary with respect to variations in the Green's function. The main information to be obtained, besides the total energy, is one-particle-like excitation spectra, i.e., spectra characterized by the quantum numbers of a single particle. This includes the low-excitation spectra in metals as well as configurations in atoms, molecules, and solids with one electron outside or one electron missing from a closed-shell structure. In the latter cases we obtain an approximate description by a modified Hartree-Fock equation involving a "Coulomb hole" and a static screened potential in the exchange term. As an example, spectra of some atoms are discussed. To investigate the convergence of successive approximations for the Green's function, extensive calculations have been made for the electron gas at a range of metallic densities. The results are expressed in terms of quasiparticle energies E(k) and quasiparticle interactions f(k, k′). The very first approximation gives a good value for the magnitude of E(k). To estimate the derivative of E(k) we need both the first- and the second-order terms. The derivative, and thus the specific heat, is found to differ from the free-particle value by only a few percent. Our correction to the specific heat keeps the same sign down to the lowest alkali-metal densities, and is smaller than those obtained recently by Silverstein and by Rice. Our results for the paramagnetic susceptibility are unreliable in the alkali-metal-density region owing to poor convergence of the expansion for f. Besides the proof of a modified Luttinger-Ward-Klein variational principle and a related self-consistency idea, there is not much new in principle in this paper. The emphasis is on the development of a numerically manageable approximation scheme. (Less)

Effects of Electron-Electron and Electron-Phonon Interactions on the One-Electron States of Solids

Abstract: Publisher Summary: This chapter discusses two major developments that have taken place over the past decade. First is the enormous wealth of energy band calculations that have had tremendous success in explaining the properties of specific solids, but in which the connection with first principles is not always apparent. Second is the spectacular progress of many-body theory applied to the solid state that has given a number of new results, although often of a rather general and formal nature, such as to provide the justification and a formal basis for a one-electron theory. The electron gas problem is treated in some detail here. The problem of the crystal potential is given due attention. It discusses the potential from the ion cores as well as from the valence electrons, and suggests schemes that incorporate essential exchange and correlation effects for the valence electrons. An energy band calculation that properly includes the effects of exchange and correlation describes the elementary excitations called quasi particles. Quasi-particle properties are usually discussed using the remarkable Landau theory of the Fermi liquid. This chapter gives a brief presentation of the theory and reviews the present status of calculations of the Fermi liquid parameters and how they are determined from experiments. (Less)

Particle-in-Cell Charged Particle Simulations, plus Monte Carlo Collisions with Neutral Atoms, PIC-MCC

Abstract: Many-particle charged-particle plasma simulations using spatial meshes for the electromagnetic field solutions, particle-in-cell (PIC) merged with Monte Carlo collision (MCC) calculations, are coming into wide use for application to partially ionized gases. The author emphasizes the development of PIC computer experiments since the 1950s starting with one-dimensional (1-D) charged-sheet models, the addition of the mesh, and fast direct Poisson equation solvers for 2-D and 3-D. Details are provided for adding the collisions between the charged particles and neutral atoms. The result is many-particle simulations with many of the features met in low-temperature collision plasmas; for example, with applications to plasma-assisted materials processing, but also related to warmer plasmas at the edges of magnetized fusion plasmas. >

Electron-phonon interactions from first principles

Abstract: The electron-phonon interaction in solids is important for many interesting properties of solids, among them the critical temperature of phonon-mediated superconductors, the effective electron mass in metals and semiconductors, and the carrier dynamics in semiconductors. Modern density-functional techniques have made it possible to perform $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations of the electron-phonon interaction. This review explains these techniques and discusses their applications.