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538 results on '"Vaclavik, J"'

254. Fine-scale structures and negative-density regions: Comparison of numerical methods for solving the advection equation

Author

Brunetti, M., Grandgirard, V., Bertrand, P., Sauter, O., Vaclavik, J., and Villard, L.

Abstract

A common feature of the Vlasov equation is that it develops fine-scale filamentation as time evolves, as observed, for example, in global nonlinear simulations of the ion-temperature-gradient instability. From a numerical point of view, it is not trivial to simulate nonlinear regimes characterized by increasingly smaller scales, which eventually become smaller than the (finite) grid size. When very small structures occur, higher order interpolation schemes have a tendency to produce overshoots and negative-density regions unless some additional dissipative procedure is applied. Different interpolation schemes for the distribution function are compared and discussed.

286. Effect of E x B flows on global linear ion temperature gradient modes

Author

Maccio, M., Vaclavik, J., and Villard, L.

Subjects
Physics::Plasma Physics, LRP 677
Abstract

Strong electric fields generate an ExB rotation of the equilibrium plasma. Experiments have shown that this effect could lower the anomalous transport in tokamaks. The study of the effect of these flows on the linear stability of ion temperature gradient (ITG) modes has therefore been undertaken. The question is addressed solving the spectrum of the gyrokinetic equation in the full two-dimensional poloidal plane for a large aspect ratio tokamak with concentric circular magnetic surfaces. Results show a strong stabilizing effect of ExB flows on the ITG modes. Study with respect to different profiles of the flow shows that the so-called curvature of flow (second derivative) has no effect, while the intensity of flow itself produces the strongest effect. Study with respect to different magnetic shears did not allow the discovery of any particular behavior of the negative magnetic shear cases. Eventually, an experimental comparison was conducted. (C) 2001 American Institute of Physics.

291. Magnetohydrodynamic waves in a non-uniform current-carrying plasma column

Author

Vaclavik, J., Weise, E., Vaclavik, J., and Weise, E.

Abstract

An effect of an axial current on the propagation of low-frequency axisymmetric magnetohydroclynamic waves in a radially non-uniform plasma column was investigated theoretically and experimentally. It was found that the axial current and the density gradient cause a coupling between the torsional and compressional waves

292. Magneto-acoustic resonance in a non-uniform current carrying plasma column

Author

Vaclavik, J. and Vaclavik, J.

Abstract

The forced radial magneto-acoustic oscillations in a plasma column with nonuniform mass density and temperature are investigated. It turns out that the oscillations have a resonant character similar to that of the magneto-acoustic oscillations in a uniform plasma column. The properties of the axial and azimuthal components of the oscillating magnetic field are discussed in detail

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