Heiji Sanuki

Compact Helical System physics and engineering design

This paper reports on the Compact Helical System designed for research on transport in a low-aspect-ratio helical system. The machine parameters were chosen on the basis of a physics optimization study. Considerable effort was devoted to reducing error fields from current feeds and crossovers. The final machine parameters are as follows: major radius of 1 m; minor radius of the helical field coil of 0.313 m; plasma aspect ratio A{sub p} = 5; pole number and toroidal period number of the helical field coil of l = 2 and m = 8, respectively; and helical pitch modulation of {alpha}{sup *} = 0.3.

Effect of Weak Dislocation Potential on Nonlinear Wave Propagation in Anharmonic Crystal

The wave propagation in an infinite one-dimensional anharmonic lattice is studied under the influence of an anharmonic potential and a weak dislocation potential. It is found that the equation for the nonlinear wave propagation has N -kink solution. The properties of one and two kink solutions are discussed in detail. It is also found that there exists the critical eigenvalue due to the competition between the above two kinds of potentials . A few conservation laws are obtained.

Spiky Soliton in Circular Polarized Alfvén Wave

A new type of nonlinear evolution equation for the Alfven waves, propagating parallel to the magnetic field, is now registered to the completely integrable family of nonlinear evolution equations. In spite of the extensive studies of Kaup and Newell, and of Kawata and Inoue, these analysis have been dealing with solutions for restricted boundary conditions. The present paper presents full account of stationary solitary wave solutions for the plane wave boundary condition. The obtained results exhibit peculiar structure of spiky modulation of amplitude and phase, which arises from the derivative nonlinear coupling term. A nonlinear equation for complex amplitude associated with the carrier wave is shown to be a mixed type of nonlinear Schrodinger equation, having an ordinary cubic nonlinear Schrodinger equation, having an ordinary cubic nonlinear term and the derivative of cubic nonlinear term.

Large Helical Device (LHD) program

The largest superconducting fusion machine, Large Helical Device (LHD), is now under construction in Japan and will begin operation in 1997. Design and construction of related R&D programs are now being carried out. The major radius of this machine is 3.9 m and the magnetic field on the plasma center is 3 T. The NbTi superconducting conductors are used in both helical coils and poloidal coils to produce this field. This will be upgraded in the second phase a using superfluid coil cooling technique. A negative ion source is being successfully developed for the NBI heating of LHD. This paper describes the present status and progress in its experimental planning and theoretical analysis on LHD, and the design and construction of LHD torus, heating, and diagnostics equipments.

New nonlocal analysis of collisionless drift wave in Vlasov plasma

The WKB‐type eigenmode analysis of an inhomogeneous Vlasov plasma is developed based on the exact integral equation. Thermal effects, namely, effects associated with the finite Larmor radius, Landau damping, cyclotron damping and so on are taken into account even if k2ρ2≳≳1 [k is of the order of ‖ψ′ (x)/ψ‖ ]. The ’’quantization condition,’’ which determines the eigenfrequency, is derived from the global localization condition of solutions. In the case of weak dissipation, this quantization condition reduces to a simple and more tractable form. Drift waves in a straight magnetic field with Gaussian density distributions are discussed numerically and analytically in detail. Results show that the growth rate of the fundamental mode (n=0) is the largest one.

Parametric Instabilities in Magnetized Plasma

The theory of parametric instabilities driven by a finite wavenumber general pump wave is developed for homogeneous magnetized plasma. The pump wave as well as the decay products can be electrostatic as well as electromagnetic. This formalism is applied to describe lower hybrid decay into electromagnetic modes. A separate treatment for the all electrostatic wave case is given using the particle drift equations. In particular the resonant decay instabilities and the oscillating two stream instabilities are studied.

Convective cell formation and anomalous diffusion due to electromagnetic drift wave turbulence

Convective cell formation and spectral cascade processes due to gravitational drift Alfven waves are studied using a new type of model equation. Conservation relations are derived and explosive instability is found for systems near marginal finite β stability. This instability also remains when the effects of poor as well as favorable curvature regions are included, i.e., for ballooning modes. The anomalous diffusion due to convective cells and quasi‐linear effects are compared.

New Treatment of Eigenmode Analysis for an Inhomogeneous Vlasov Plasma

A new eigenmode analysis is presented for an inhomogeneous Vlasov plasma based on an integral equation in the wavenumber space. The effects of finite Larmor radius can be taken into account even for the case of \(k \rho _{i} \gtrsim 1\) where k is a measure of the wavenumber in the direction of spatial inhomogeneity and ρ i is the ion Larmor radius. The eigenfrequency is determined from a compact “quantization condition” which is an extension of the Bohr-Sommerfeld “quantization condition” for second order differential equations.

Effects of Landau Damping on Nonlinear Wave Modulation in Plasma

On the basis of the Vlasov equation, an equation to describe behaviour of the electric potential is obtained for small but finite amplitude waves in a plasma. Under a certain stretching scheme, the equation is reduced to the generalized nonlinear Schrodinger equation \(i\frac{\partial\psi}{\partial\zeta}+\alpha\frac{\partial^{2}\psi}{\partial\eta^{2}}+\beta|\psi|^{2}\psi+i\gamma\psi{=}0\), where α and β are constants (αβ<0) and γ means the damping constant. The decay process of the nonlinear electron plasma wave is investigated on the basis of this equation. It is found that the soliton can exist for finite time interval, and under a certain condition the amplitude of soliton grows first and then damps away.

Perturbation Theory of the Nonlinear Plasma Wave with Landau Damping

A generalized Korteweg-de Vries type equation is obtained for small but finite amplitude waves in plasma by treating the Vlasov equation perturbation theoretically. The influence of ion Landau damping on the ion sound soliton is discussed. Even if the ion acoustic wave is stable, it is shown that under a certain condition the amplitude of soliton grows in time. In the case of the unstable ion acoustic wave, the amplitude of soliton saturates at the finite value.