Search

A transport threshold model of subsonic neoclassical tearing modes (NTMs) in tokamaks is developed. The basic procedure is to include the velocity-dependent term into the single-fluid heat-conductivity equation and to complement this equation with the single-fluid parallel plasma motion equation. These equations permit the determination of the perturbed plasma temperature and the bootstrap current drive of NTMs, for both strong and weak perpendicular heat transport, which is the precondition for developing the above model. It is shown that the subsonic NTMs transport threshold model can be more realistic than the standard transport model of NTMs suggested by Fitzpatrick [Phys. Plasmas 2, 825 (1995)]. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The problem of drift stabilization of the internal resistive-wall modes (RWMs) in tokamaks is theoretically investigated. The basic assumption of the model is that, when the drift effects are neglected, these modes are unstable in the absence of a conducting wall and stable in the presence of a close-fitting perfectly conducting wall. In the former case, the instability condition is expressed as Δ[sub ∞][sup ′] > 0, where Δ[sub ∞][sup ′] is the matching parameter calculated under the assumption that the wall is removed to infinity. In the latter case, one has Δ[sub W][sup ′] < 0, where Δ[sub W][sup ′] is the external matching parameter of tearing modes calculated assuming a perfectly conducting wall at the plasma boundary. In the case with a resistive wall, the relevant parameter can be either Δ[sub ∞][sup ′] or Δ[sub W][sup ′] , depending on whether the value of the dimensionless parameter ωτ[sub s] /2m is small or large, respectively (here ω is the mode frequency, τ[sub s] is the resistive time constant of the wall, and m is the poloidal mode number). In the presence of drift effects, the mode frequency ω is approximately equal to the electron drift frequency, ω ≈ ω[sub *e]. The value of the parameter ω[sub *e]τ[sub s] /2m, which therefore determines the behavior of internal RWMs, is estimated for several existing tokamaks, namely, AUG (ASDEX-Upgrade), DIII-D, JET, TFTR, and JT-60U, as well as for the projected ITER-FEAT. It is shown that, although drift effects do not stabilize internal RWMs in current devices, they should be efficient in suppressing these modes in reactor-grade tokamaks. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Investigates the suppression of anomalous transport and/or reduction of neoclassical transport caused by the Alfven-wave-induced shear of the radical electric field in tokamaks. Radial variations of the ion viscosity and heat conductivity across the mode conversion layer; Role of the kinetic Alfven waves.

Discusses how Alfven waves and fast wave forces affect ions in magnetic traps with closed magnetic surfaces. Calculation of Alfven or fast wave forces in stellarators; Computer simulations of the transport barrier formation by Alfven and fast waves in toroidal devices.

Investigates the plasma rotation in toroidal devices with circular cross-sections. Dependence of magnetic axis curvature and torsion on the longitudinal coordinate and magnetic field ripples; Analysis of the ion poloidal velocity in the Pfirsch-Schluter regime.

Reports on a general approach to the Alfven wave current drive problem in tokamaks with elongated transverse cross-sections. Use of model approximations to describe circulating and trapped particle dynamics; Expressions for the time-averaged longitudinal current and radio-frequency currents.

Studies the general aspects of the Alfven and fast wave nonresonant and resonant current-drive problem for collisional and weakly collisional plasmas. Application of the magnetohydrodynamic approach for collisional regimes and Landau damping; General form of current-drive forces.

Investigates the role of the density gradient of hot ions in tokamaks in the toroidal Alfven eigenmode (TAE) problem when the shear is less than the local inverse aspect ratio. Linearized current-continuity equations; Perturbation mode consisting of the mth and (m-1)th poloidal harmonics.

Focuses on the formation of edge and internal transport barriers in tokamaks. Use of Alfven waves in the analysis; Methods of triggering the internal transport barriers; Types of instabilities in tokamak edge plasmas.

Focuses on the effect of radio frequency fields on a plasma rotation in the edge region of slightly rippled tokamaks. Expressions for poloidal and toroidal velocities and for quasistationary radial electric fields; Modification of the rotation velocities and radial electric fields in collisional regions of tokamak plasmas by Alfven waves.