Yoichiro Furutani

Effective Potential of a Partially Ionized High-Z Ion

Within the framework of the density functional theory (DFT), we have computed numerically the effective potential of a partially ionized high-Z ion and the associated radial profile of the electron density for temperatures ranging from T =0 to high temperature regimes of several hundreds eV.

Nonlinear coupling of the slow wave structure with the lower-hybrid waves near the plasma surface

Nonlinear coupling between the slow mode launched by a waveguide array and a plasma slab near the plasma surface is investigated as the problem of the one-dimensional steady-state wave propagation in an inhomogeneous plasma. Numerical analysis based on the nonlinear equation for an electric field with two different density profiles is extensively carried out and is compared with results analytically obtained from the model with a shifted linear density profile which globally accounts for the effect of the ponderomotive force.

Two-Center Problem for a Dense Plasma

The Thomas-Fermi-Dirac-Weizsacker statistical model of atoms is applied to a compressed diatomic molecule in a dense plasma. As a two-dimensional problem, we analyze numerically a spatial profile of the screening function and the electron density inside a closed boundary surface. We also calculate the Helmholtzs excess free energy as a function of the internuclear distance, to examine a possibility of the binding state.

Nonlinear Wave Modulation in a Magnetized Collisionless Plasma

Nonlinear modulation of quasi-monochromatic electromagnetic waves propagating parallel to an external magnetic field is investigated with particular attention to contributions of resonant particles at the group velocity. The contributions of these resonant particles give rise to a nonlocal-nonlinear tram and modify the local-nonlinear term of the nonlinear schrodinger equation. An explicit expression of a coefficient of the nonlocal-nonlinear term is given for a plasma characterized by isotropic Maxwellian velocity distribution functions. In a vanishing temperature limit this coefficient becomes zero and the nonlinear Schrodinger equation agrees with that obtained by using a fluid model.

One-Electron State of a Partially Ionized High-Z Ion

An effective potential of an isolated partially ionized high-Z ion, calculated within the framework of the statistical models of atoms, is injected into the one-electron Schrodinger equation, in view of evaluating the electron density and comparing it with the results of statistical models. Starting from this initial value, a self-consistent electron density is obtained on the basis of the density functional theory, where quantum natures of electrons are fully taken into account.

Numerical Simulation for ICRF Minority-Ion Heating in a Tokamak

Ion cyclotron range of frequencies (ICRF) heating in the two-ion hybrid resonance regime is numerically studied and the results are compared with those of the heating experiments on the JET tokamak. The kinetic one-dimensional analysis of the ICRF wave is coupled with the anisotropic Fokker-Planck equation and the one-dimensional transport code, Spatial transport coefficients are inferred from those of the drift wave model and a phenomenological internal disruption is introduced. Calculated power deposition profiles agree well with experimental results. Degradation of confinement with increasing heating power, profile modification due to the off-axis heatinq and heat pulse propagation after the internal disruption are well reproduced by our simulation model.

A new method for analyzing an anisotropic velocity distribution in ICRF-heated plasmas

A new approximation method has been devised, for analyzing a time evolution of the resonant-ion velocity distribution during the ion cyclotron heating of a plasma. A strong anisotropy of the wave-induced high energy tail is described by the expansion in terms of the parallel velocity moments. A portion of higher order terms is retained in order that the Maxwellian be a steady state solution, with no RF power. Numerical analysis confirms that the velocity distribution is close to that obtained from the full two-dimensional analysis and that a computation time is reduced considerably. An applicable range of the RF power density is much wider than that found by other approximation methods.

Nonlinear Behaviour of Lower Hybrid Waves near the Linear Mode-Conversion Point

The nonlinear behaviour of the two-dimensional steady-state propagation of the lower hybrid wave near the linear mode-conversion point is investigated in the presence of the density depression due to the ponderomotive force. It is shown that an equation which governs the wave packet near the conversion point can be reduced to the nonlinear Schrodinger equation with a Iinearly increasing potential. Numerical analysis of the model equation visualizes the behaviour of the wave packet in the linear and the nonlinear regimes.

Two‐temperature model of atoms in dense plasmas

To analyze the internal structure of a compressed atom or ion immersed in dense plasmas, many theoretical schemes, such as orthodox Hartree‐Fock‐Slater method, time‐honored statistical theory of atoms and a more systematic density functional theory, have been devised and developed. In this article, we propose the two‐temperature model of atoms, composed of an ion core in its ground state (T=0) and a clad electron gas at finite temperatures (T>0), the latter being held in thermal equilibrium with a surrounding dense plasma. We analyze the model with recourse to the Thomas‐Fermi‐Dirac‐Weizsacker statistical theory and present several results. Throughout this article, the atomic units are used, unless otherwise specified.

Two-Temperature Model of Compressed Atoms in a Dense Plasma

We propose and analyze the two-temperature model of compressed atoms, immersed in a dense plasma, which is composed of an ion core in its ground state ( T =0) and a clad electron gas at finite temperatures. They are out of thermal equilibrium. The profiles of the electron density and the screening function within the atom are calculated numerically on the basis of the variational Thomas-Fermi-Dirac-Weizsacker equation. A limit of validity of the model is also discussed.