Haruichi Washimi

Self-Focusing of Transverse Waves in a Magnetoplasma

The self-focusing of the transverse waves (comprising the whistler, Alfvenic and electromagnetic modes) propagating along an applied magnetic field in a plasma of finite temperature is discussed. The method of stretching which has been used by Taniuti and Washimi 5) is applied. It is shown that behaviours of the wave amplitude are described by the nonlinear Schrodinger equation and that the threshold power for the self-focusing becomes very small not only at the special frequency for the whistler wave which was already obtained in the previous paper 5) but also at a frequency for the Alfven wave. The expression of the coefficient of the nonlinear term of the nonlinear Schrodinger equation is revised.

Magnetic Field Generation Due to Ponderomotive Force in a Plasma

Slowly varying magnetic field is found to be generated by the ponderomotive force of the electromagnetic wave (slowly-varyjng in time) incident into an isotropic, homogeneous and collisionless plasma. Magnitude of the magnetic field is estimated for laser-produced plasma.

Method for Analyzing Nonlinear Wave Propagation and Wave-Trapping in Magnetoplasmas

A new method of perturbation for the study of nonlinear wave propagation in a magnetoplasma is proposed under the condition that the dielectric tensor of the plasma changes slowly in time and space. Using this method, we derive a generalized nonlinear wave equation for the transverse waves propagating along magnetic field lines, which includes the effects due to the ponderomotive force or due to an inhomogeneity of the plasma. The physical condition is elucidated for the wave-trapping in two- or three-dimensional space which comes from a negative-pressure effect of the ponderomotive force or the inhomogeneity.

Lower hybrid resonance wave excitation by whistlers in the magnetospheric plasma

A new theory of lower hybrid resonance (LHR) wave excitation by whistlers in magnetospheric plasma is developed. Two time dependent differential equations, which have a form of linear wave interaction between quasi-longitudinal whistler-mode waves and quasi-electrostatic LHR waves in a cold plasma with small-scale density irregularities, are derived and solved by the method of successive approximations. Fundamental observational results on LHR wave excitation by whistlers, such as the lower cutoff frequency of excited waves and the pronounced spectral maximum near the LHR frequency, as well as the close connection of the excitation process with small-scale plasma density irregularities are explained by the present theory in a consistent manner.

Wave-Trapping in an Inhomogeneous Magnetoplasma

The multi-dimensional wave equations for the waves propagating along a magnetic field in an inhomogeneous plasma are derived and the wave-trapping is discussed. It is shown that the wave equations are reduced to the Schrodinger-type ones in which the sign of the coefficient of the second derivative depends on (ψ/θ) θ=0 where ψ is the angle between the field line and the ray, and θ is the angle between the field line and the wave normal. The physical reason of the wave trapping is explained by comparing the sign of (ψ/θ) θ=0 with that of the effective potential in the wave equation. As an example, the wave trapping of the whistler wave in geo-magnetosphere is considered.

A simulation study of the solar wind including the solar rotation effect

An axisymmetric solar wind structure including the solar rotation effect is studied by the method of MHD computer simulation. For the case of the radial magnetic field configuration, the simulation result is fairly well coincident with the steady-state solution. For the case of the dipole magnetic field configuration, the properties of the solution depend on the ratio of the gas pressure to the magnetic pressureβ-ratio) in the model. If theβ-ratio is small, a clearly defined stagnation region appears in the wind, in which the flow speed is very small and the azimuthal magnetic field is very weak because of the corotation of the plasma. If theβ-ratio is greater than 1, the plasma is not effectively trapped by the magnetic field so that the stagnation region is not clearly defined in the solution.

Electrostatic Potential in the Endcells of a Tandem Mirror under Electron Cyclotron Resonance Heating

The electrostatic potential profile in the endcells of a tandem mirror under electron cyclotron resonance heating is studied by including an ionization process. A plug potential is found to form with a combination of created ions by ionization, wave-heated electrostatically trapped electrons and mirror trapped electrons, but without a help of high energy sloshing ions. In the present model the electrostatic potential has its maximum at the outer mirror throat of end mirror cell.

Self-Focusing of Ion Wave in Plasma with Negative Ion

Self-focusing of an ion wave in a plasma composed of electron, positive ion and negative ion has been investigated theoretically. A nonlinear Schrodinger equation which describes the spatial development of ion wave is derived and the signs of nonlinear and dispersion coefficients are examined by use of this equation. The dispersion coefficient is positive in the whole wavenumber range. The nonlinear coefficient vanishes at a critical wavenumber k c , above which the coefficient becomes positive and the ion wave is unstable with respect to transverse modulation. At the critical density of negative ion, the critical wavenumber k c is reduced to zero and the self-focusing occurs for ion wave of small wavenumber.

Observations of Interplanetary Scintillation and a Theory of High-Speed Solar Wind

It has been confirmed that the high-speed solar wind flows out of the coronal holes at low latitudes, where the magnetic fields open and the temperature is low (e.g., Krieger et al. 1973). But there has not been direct observation of the solar wind out of the polar regions of corona. We report here that the observations of interplanetary scintillation (IPS) show the existence of the high-speed flow of 800 km/s out of the polar coronal regions and the well-coincidence to the model of the coronal holes extending from the polar regions.