Sanae Inoue

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.

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.

Electrostatic Drift Instability of Tokamak Plasmas

We present a comprehensive theory of the electrostatic drift instabilities of a collisionless plasma in a toroidal device. The effects of inhomogeneities (density, electron and ion temperature gradients), plasma current, radial electric field, magnetic shear and toroidal curvature drift are simultaneously examined; we derive the general but simple criteria for the drift stability. The instabilities are found to be excited owing to the plasma current, ion temperature gradient, curvature of ion cross-field flow and toroidal effects, although the magnetic shear has a prominent stabilizing power. Drift waves are expected to be almost always unstable in tokamak plasmas.

Critical Conditions for Drift, Drift-Alfven and Drift-Tearing Instabilities of Finite-β Plasma in Sheared Magnetic Field

Kinetic theory of low frequency instabilities of a current-carrying finite-β plasma in a sheared magnetic field is investigated. Drift mode, drift-Alfven mode and drift-tearing mode are identified both in collisionless and collisional regimes and each critical stability condition is obtained, We find a new electromagnetic localized mode driven by the plasma current in a finite-β plasma. Both the current and finite-β effects are required to excite this mode. It is also shown that, in the absence of the plasma current, any electromagnetic localized mode which is propagating in the direction of the electron diamagnetic drift is stable in the collisionless limit of a finite ion temperature plasma. For the collisional mode, stability holds if ω>ω * (electron diamagnetic frequency) or ω<0.

Comments on ’’Resistive drift‐Alfvén waves in sheared magnetic fields’’

In contradition of the result obtained by Catto et. al. the collisional drift‐Alfven mode in a sheared magnetic field is shown to be stable. The validity of an expansion used by Catto et al. is questioned. (AIP)

A Scaling Law for High Density Tokamaks and Its Application to J.I.P.P. T-II Device

A scaling law for high density and high current tokamaks is presented on the basis of the nonlocal theory of electrostatic current-driven drift instability in both collisionless and collisional regimes with the assumption of quasilinear saturation level. It is shown that the energy confinement time scales as \(\tau_{E}{\propto}nq(a)/\sqrt{T_{e}}\) ( n , T e and q ( a ) are the averaged density, electron temperature and the safety factor at the plasma edge.) in relatively lower density region and \(\tau_{E}{\propto}B/\sqrt{n}\) ( B is the toroidal magnetic field) in higher density region where a combined effect of the electron collisions and of a plasma current works. Trapped particle effects are assumed to be negligible and no magnetic fluctuation is considered. A test experiment of the scaling law on the J.I.I.P.T-II device where both tokamak operation and the operation with superposition of helical fields are possible is proposed.

Toroidal Effects on Nonlocal Collisionless Drift Instability

Toroidal curvature effects on the electrostatic collisionless drift instability in a sheared magnetic field is investigated. The magnetic curvature drift of ions reduces or even annihilates the shear convective damping and causes the mode ballooning. It is found that the universal mode is stable (or marginally stable at most) so long as the convective damping remains finite, and the critical current density for the current-driven drift instability becomes lower.

Nonlinear Magnetohydrodynamic Instability and Disruptive Instability

A new model of the disruptive instability is presented. Nonlinear MHD instability of m = n =0 mode is solved in a cylindrical tokamak configuration. The stability threshold of this mode is obtained in terms of the amplitude of the co-existing higher m mode instabilities. Below the threshold, this mode has finite amplitude, and above the threshold, it grows catastrophically. The experimental characteristics of the disruptive instability well conform to the properties of the m = n =0 nonlinear MHD instability.

Shear Stabilization of Collisional Drift Instability

Using the normal mode expansion method, the collisional drift waves of the slab plasma in a sheared magnetic field are investigated. In the strong shear parameter regime, \(1{\lesssim}\kappa L_{s}{\ll}m_{i}/m_{e}\) (κ: density gradient, L s : shear length and m i / m e : ion to electron mass ratio), the growth rate is found to be proportional to \(\sqrt{\nu/\omega_{*}}\). The diffusion coefficient is also estimated and a density limitation of high density tokamak is shown.

Helical Resonance in Tokamak Equilibrium

Helical equilibria of tokamak are investigated with the self-consistent equilibrium equation. These are divided into three cases; 1) The shell is circular without an error field, 2) circular shell with external helical field such as helical windings field, and 3) the shell is helically deformed. In the first case, helical equilibrium is found for a particular q value. In the second case, an equilibrium is found for any q value, and there appears the resonance of the plasma with the external field. The plasma deformation is found to be very large for the imposition of a slight helical field. And for the last case, the analysis gives the similar result as the second case. These resonant phenomena cannot be derived from the mere superposition of the fields.