Abstract
A novel method of perturbation analysis has been developed to characterize particle and energy confinement in a tokamak plasma. Whereas the classical approach to confinement begins with an empirical model using transport coefficients, the present work uses eigenmodes to represent the dynamic response. The latter approach has been applied to density perturbations induced in the TCA tokamak by pellet injection. The observed dynamic response can be entirely reproduced by a set of three eigenmodes, thereby reducing the temporal evolution of the density to three time constants only. The scatter of these time constants allows the density to evolve on quite different time-scales, with the relaxation of the density profile being determined by the nature of the eigenmodes. Whilst a {tau}{approx}I{sup 2-3}{sub p}n{sup o}{sub e} dependence is observed in the time constants, the eigenfunctions remain insensitive to plasma conditions. The density invariance is linked with a strong linearity in the dynamic response, indicating that the pellet has no significant impact on transport processes. The eigenmode representation is particularly well suited to the study of coupled variables. A coupling has been identified between density perturbations and another variable which is very likely to be the electron temperature. The strength of this coupling
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Dudok de Wit, T
[1]
- Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP)
Citation Formats
Dudok de Wit, T.
Decomposition into eigenmodes: a novel approach to characterize plasma confinement in a tokamak; La decomposition en modes propres: une approche nouvelle pour caracteriser le confinement du plasma dans un tokamak.
Switzerland: N. p.,
1992.
Web.
Dudok de Wit, T.
Decomposition into eigenmodes: a novel approach to characterize plasma confinement in a tokamak; La decomposition en modes propres: une approche nouvelle pour caracteriser le confinement du plasma dans un tokamak.
Switzerland.
Dudok de Wit, T.
1992.
"Decomposition into eigenmodes: a novel approach to characterize plasma confinement in a tokamak; La decomposition en modes propres: une approche nouvelle pour caracteriser le confinement du plasma dans un tokamak."
Switzerland.
@misc{etde_10144865,
title = {Decomposition into eigenmodes: a novel approach to characterize plasma confinement in a tokamak; La decomposition en modes propres: une approche nouvelle pour caracteriser le confinement du plasma dans un tokamak}
author = {Dudok de Wit, T}
abstractNote = {A novel method of perturbation analysis has been developed to characterize particle and energy confinement in a tokamak plasma. Whereas the classical approach to confinement begins with an empirical model using transport coefficients, the present work uses eigenmodes to represent the dynamic response. The latter approach has been applied to density perturbations induced in the TCA tokamak by pellet injection. The observed dynamic response can be entirely reproduced by a set of three eigenmodes, thereby reducing the temporal evolution of the density to three time constants only. The scatter of these time constants allows the density to evolve on quite different time-scales, with the relaxation of the density profile being determined by the nature of the eigenmodes. Whilst a {tau}{approx}I{sup 2-3}{sub p}n{sup o}{sub e} dependence is observed in the time constants, the eigenfunctions remain insensitive to plasma conditions. The density invariance is linked with a strong linearity in the dynamic response, indicating that the pellet has no significant impact on transport processes. The eigenmode representation is particularly well suited to the study of coupled variables. A coupling has been identified between density perturbations and another variable which is very likely to be the electron temperature. The strength of this coupling does not depend on plasma conditions, although it varies with the level of MHD activity. High levels of activity change the interaction between particle and heat fluxes without affecting the eigenmodes. This results in an unfavourable weighting of the eigenmodes which accelerates the density relaxation and thereby explains the observed confinement degradation. (author) 42 figs., 45 refs.}
place = {Switzerland}
year = {1992}
month = {Oct}
}
title = {Decomposition into eigenmodes: a novel approach to characterize plasma confinement in a tokamak; La decomposition en modes propres: une approche nouvelle pour caracteriser le confinement du plasma dans un tokamak}
author = {Dudok de Wit, T}
abstractNote = {A novel method of perturbation analysis has been developed to characterize particle and energy confinement in a tokamak plasma. Whereas the classical approach to confinement begins with an empirical model using transport coefficients, the present work uses eigenmodes to represent the dynamic response. The latter approach has been applied to density perturbations induced in the TCA tokamak by pellet injection. The observed dynamic response can be entirely reproduced by a set of three eigenmodes, thereby reducing the temporal evolution of the density to three time constants only. The scatter of these time constants allows the density to evolve on quite different time-scales, with the relaxation of the density profile being determined by the nature of the eigenmodes. Whilst a {tau}{approx}I{sup 2-3}{sub p}n{sup o}{sub e} dependence is observed in the time constants, the eigenfunctions remain insensitive to plasma conditions. The density invariance is linked with a strong linearity in the dynamic response, indicating that the pellet has no significant impact on transport processes. The eigenmode representation is particularly well suited to the study of coupled variables. A coupling has been identified between density perturbations and another variable which is very likely to be the electron temperature. The strength of this coupling does not depend on plasma conditions, although it varies with the level of MHD activity. High levels of activity change the interaction between particle and heat fluxes without affecting the eigenmodes. This results in an unfavourable weighting of the eigenmodes which accelerates the density relaxation and thereby explains the observed confinement degradation. (author) 42 figs., 45 refs.}
place = {Switzerland}
year = {1992}
month = {Oct}
}