Toshio Tange

Anomalous Transport Due to Electromagnetic Fluctuations across a Magnetic Field

A general theory is presented for the transport fluxes across a magnetic field due to electromagnetic fluctuations. The transport coefficients are expressed in terms of the spectral functions or the correlation functions of the fluctuations under the assumption that the scale length of the inhomogeneity is large as compared with the ion Larmor radius. As a simple application of the formulas obtained, we investigate the finite-β effects on the diffusion and the heat fluxes of electrons due to the drift wave turbulence neglecting the effect of the magnetic shear. We find that these fluxes are reduced by the finite-β effect.

Numerical Analysis of Current-Driven Drift-Wave Instability in a Finite-β Plasma

Stability of the collisionless drift wave localized to the rational surface is studied numerically. Both the current and the finite- β effects are taken into account. The results confirm the previous analytical and/or numerical results concerning the stableness in the currentless case, instability driven by the current and its finite- β stabilitzation in the short wavelength region. In addition, a strong resonant coupling of the drift wave to the Alfven wave is found to occur due to the combined effect of the current and the finite- β value, resulting a destabilizing effect in the long wavelength region. The critical electron drift velocity for the onset of the instability is calculated. The result shows a substantial reduction of the critical velocity by the finite- β effect.

Magnetic field generation due to resonance absorption

A detailed study of the mechanism of mega‐Gauss magnetic field generation in the resonant absorption of laser light is presented which takes into account the effects of both the dissipation and thermal motion of electrons.

Anomalous ion loss due to low-frequency instabilities

An ambipolarity formula for the cross-field flux of non-uniform plasma in the presence of low-frequency (ω ion gyrofrequency) electromagnetic fluctuations is presented. It is shown that, owing to ion polarization drift, the ions are pulled out by the diffusing electrons.

Diffusion of a Multi-Ion Species Plasma Due to Drift Wave Fluctuations

A general theory is presented for the diffusion of a multi-ion species plasma across magnetic field due to electrostatic fluctuations. The theory is based on the weak turbulence theory for an isothermal plasma in a slab geometry. The diffusion flux due to wave-particle interactions was shown to be not necessarily proportional to the density gradient of the particle species of interest. The result is applied to the impurity diffusion due to those drift waves which exist in a single ion-species plasma. The dominant nonlinear effect is the scattering of waves on ions and the resulting diffusion constant of the host ions is derived. The impurity diffusion constant is positive (or negative) if the impurity Larmour radius is smaller (or greater) than the host-ion Larmour radius, and becomes greater than the host diffusion constant if the spectrum is localized in the unstable region.

Nonlinear saturation of drift waves in sheared magnetic field

A nonlinear saturation mechanism of electrostatic drift waves in a sheared magnetic field is presented. The basic physical mechanism is the coupling of the unstable, lowest radial mode to higher modes which are damped because of their short radial wavelengths. Stationary spectra are obtained analytically and applied to the current‐driven drift wave instability.

Criterion for Absolute Instability of a Wave in a Nonuniform Medium

Using a model equation which describes the wave propagation with a step like localized energy source, we examined the criterion for absolute instability of the wave localized to the source region. Both the case of an optical mode with a step like localized potential well or anti-well and the case of an acoustic mode with zero potential are investigated. It is shown that the absolute instability can occur either when the wave is trapped in the localized source region, or when the wave is untrapped but the source strength exceeds a threshold value. For the case of the acoustic mode, the threshold of the local growth rate is given by the convection damping rate, while for the case of the optical mode with anti-well potential, it first increases proportionally to the potential height, but soon saturates to 1.2 times the local convection damping rate.

Nonlinear Stability of Drift Wave in a Sheared Magnetic Field

A nonlinear eigenvalue equation for drift wave in a sheared magnetic field is derived by summing the most secular terms of nonlinear electron response. Restricting ourselves to the case where the wave is monochromatic and its amplitude is small, we numerically investigated amplitude dependence of the eigen-frequency. The drift wave is found to be destabilized as the fluctuation amplitude increases.

Effect of RF-Driven Current on Stability of Drift Wave

Stability of electrostatic drift waves in a plasma carrying an electron current driven by a radio frequency wave is investigated. Numerical calculation of the growth rate of the drift wave in a sheared magnetic field is made for a slab model with a bi-Maxwellian electron distribution. It is found that the RF-driven current acts to destabilize the drift wave but the destabilizing effect is much weaker than that of the Ohmic current.