Akademik Veri Yönetim Sistemi
NUCLEAR FUSION, cilt.46, sa.4, 2006 (SCI-Expanded)
The impact of helical perturbations on the rotation velocity and thus on the energy confinement is calculated on the basis of the ambipolarity constraint, the parallel momentum equation of the revisited neoclassical theory and a simplified temperature equation. The helical perturbations can act as means for ergodizing the magnetic field and/or as momentum source or sinks, whereas at the separatrix (effective radius r(s)) of the poloidal divertor a temperature pedestal may arise due to the strong shear flow reducing the transport to a neoclassical level. The neoclassical theory allows the prediction of the parallel and poloidal flow speeds and thus of the 'subneoclassical' heat conductivity chi(sub) used in the heat conduction equation. This heat conductivity allows us to compute the temperature pedestal and to reproduce the power balance in ALCATOR if one assumes that chi = chi(sub) in the radial sheath with the thickness of Delta approximate to 0.7 cm, centred around the inflection radius r(in), and chi = chi(L) for r < r(in) - Delta/2. chi(L) is the normal L-mode heat conductivity. Source terms account for momentum deposition by neutral beam injection (NBI), by pressure anisotropization and the j x B force density, the latter two due to Fourier components of (rotating) helical fields.