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537 results on '"Vaclavik, J"'

206. Gyrokinetic modelling of macro-instabilities in high performance tokamak plasmas

Author

Jaun, A., Fasoli, A., Testa, D., Vaclavik, J., and Villard, L.

Subjects
JET
Abstract

The modelling of Alfvenic instabilities is discussed from the point of view of mode-conversion, showing how the development of the theory affects the predictions as the limitations of the models are gradually relaxed. Conventional tokamak plasmas are relatively well understood and are used for the case of a kinetic Alfven eigenmode (AE) to assess the resonant wave-particle interactions along the magnetic field. The large safety factor in the core of deeply reversed shear plasmas and the low magnetic field of spherical tokamaks, however, bring the AEs down into the drift-frequency range; modifications of the spectrum through toroidal mode-conversion then creates a new class of drift-kinetic AEs that could affect the fast particle confinement. Experiments have been carried out to verify these predictions in JET. They confirm the presence of weakly damped modes, which do not follow the usual AEs scaling.

223. Dielectric Tensor Operator of Hot Plasmas in Toroidal Axisymmetrical Systems

Author

Brunner, S. and Vaclavik, J.

Subjects
Physics::Plasma Physics
Abstract

Kinetic theory is used to develop equations describing dynamics of small-amplitude electromagnetic perturbations in toroidal axisymmetric plasmas. The closed Vlasov-Maxwell equations are first solved for a hot stationary plasma using the expansion in the small parameter epsilon(e) = rho/L, where rho is the Larmor radius and L a characteristic length scale of the stationary state. The ordering and additional assumptions are specified so as to obtain the well-known Grad-Shafranov equation. The dielectric tensor of such a plasma is then derived. The Vlasov equation for the perturbed distribution function is solved by the expansion in the small parameters epsilon(e) and epsilon(p) = rho/lambda, where lambda is a characteristic wavelength of the perturbing electromagnetic field. The solution is obtained up to the first order in epsilon(e) and the second order in epsilon(p). By integrating the resulting distribution function over velocity space, an explicit expression for the tensor is derived in the form of a two-dimensional partial differential operator. The operator is shown to possess the proper symmetry corresponding to the energy conservation law.

238. Alfvén wave heating

Author

Appert, K., Succi, S., Vaclavik, J., and Villard, L.

Subjects
LRP 223

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