Tadatsugu Hatori

Radio-frequency plugging of a high density plasma

Mirror end loss can be suppressed by applying an rf field at the mirror throat through low impedance coils. This method is verified to be effective for a high density plasma up to 1014 cm−3. Experimental results show that the rf field strength required for the plugging is dependent on the plasma density. The dependence differs according to the geometry of the coil. The mechanism of giving the density dependence is theoretically clarified for each coil. Particularly, it is shown that the electric field induced in the direction of the static magnetic field is intrinsic for the result of type‐III coil where its efficiency for rf plugging is insensitive to the plasma density.

Stochastic diffusion in the standard map

Abstract A numerical observation of stochastic diffusion in the standard map has been carried out in the domain of small stochastic parameter A c A A c is given as (2 π ) −1 ×0.9716 = 0.1546. Multiple periodic accelerator modes manifest their pronounced sharp resonant effect in the stochastic diffusion process even in the region of small stochastic parameter, where the fundamental accelerator modes are not allowed to exist.

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

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 mo...

Kolmogorov-Style Argument for the Decaying Homogeneous MHD Turbulence

Similarity solutions for 2D MHD and 3D MHD turbulence are obtained assuming the invariance of the mean square magnetic potential and the magnetic helicity respectively in the limit of infinite Reynolds number. The temporal decay laws of the energy, the cross-helicity and the magnetic helicity are derived from these similarity solutions. The present conjecture concerning the decay process is discussed in comparison with the one employed by J. B. Taylor (1974).

Turbulent diffusion for the radial twist map

Abstract An analytical tool is given to study the statistical properties of the radial twist map, Xn+1 = Xn + α(Yn+1) and Yn+1 = Yn + Af (Xn), with arbitrary rotation number α(Y) and arbitrary periodic force f(X). The case for which f(X) = sin 2 πX and with arbitrary α is treated in the region of large A. The turbulent diffusion coefficient D for the chaotic orbit relaxes as t − 1 2 to A 2 4 , except for the case of the standard map, where the eventual value of D is different from A 2 4 .

Evaluation of improved efficiency with a diamond coating for a plasma display panel electrode

Application of diamond to electrode coating of a plasma display panel (PDP) is evaluated, since we expect diamond to emit much secondary electron due to the Auger neutralization induced by Xe ions. In a conventional magnesium oxide-xenon (MgO/Xe) system, the most abundant Xe+ produced in the discharge does not effectively cause the secondary electron emission, because the condition of the Auger neutralization is not satisfied. In order to increase the efficiency of ultraviolet (UV) radiation, being especially important for engineering, we should avoid such inefficiency. Under suitable conditions in diamond/Xe system the Auger neutralization can occur. Further, if the electron affinity χ is negative, i.e., negative electron affinity (NEA), the condition of the Auger neutralization in diamond/Xe system is sufficiently satisfied. First, we calculate the coefficients of the secondary electron emission on diamond of clean surface or of hydrogenated surface where the dangling bonds are terminated, on the basis ...

Asymptotic Expansion of Nonlinear Unstable Collisional Drift Wave

Nonlinear evolution equation for the collisional drift wave is obtained in a stab model based on the two fluid equations where the ton inertia, finite gyroradius and viscosity are included. A systematic expansion is introduced by taking e =|κ| l as a smallness parameter where κ is the degree of density gradient and l is the linear scale of the stab along the density gradient. A set of the model equations is proposed to describe the evolution of the nonlinear drift wave.

Chaotic reconnection due to fast mixing of vortex-current filaments

We propose a new reconnection mechanism “chaotic reconnection”. A basic mechanism of the chaotic reconnection is examined by means of numerical simulations of collision between two vortex-current filaments. The term “reconnection” means a reconnection of the filaments. We conclude that thle chaotic process works to enhance the reconnection rate of the filaments. We shall propose a similar chaotic process as a candidate for the mechanism of the fast magnetic reconnection.

Filamentary magnetohydrodynamic simulation model, current-vortex method

A two-dimensional simulation model of the “magnetohydrodynamic (MHD)” vortex method, current-vortex method, is developed. The concept is based on the previously developed current-vortex filament model in three-dimensional space. It is assumed that electric current and vorticity have discontinuous filamentary (point) distributions on the two-dimensional plane, and both the point electric current and the point vortex are confined in a filament. In other words, they share the same point on the two-dimensional plane, which is called the “current-vortex filament.” The spatial profiles of the electric current and the vorticity are determined by the sum of such filaments. Time development equations for a filament are obtained by integrating the two-dimensional MHD equations around the filament. It is found that a special-purpose computer, MDGRAPE-2, is capable not only of molecular dynamics simulations but also of MHD simulations, because MDGRAPE-2 accelerates calculations of the Biot–Savart integral. The curren...

Numerical Simulations of the Vortex-Current Filaments Motion

Motion of the vortex-current filaments is examined via cutoff Biot-Savart numerical MHD simulations of single and double filaments. We have introduced a vortex-current filament by analogy with the vortex filament. The vortex-current filament consists of electric current density and vorticity which are parallel to the axis of the filament. Attention is needed to demonstrate the difference between vortex and vortex-current filaments. In this paper we present two numerical results of vortex-current filament motion, using cutoff Biot-Savart method. In the limit of no electric current, the two results are in good agreement with vortex filament systems. The first result is obtained for two circular ring filaments. Here we find there are some cases where the qualitative characteristics of the motion are unchanged by introducing electric current along the vorticity. On the other hand, the period of the mutual slipping motion of the filaments is changed. The second result is related to oscillation of an elliptic r...