Verlag des Forschungszentrums Jülich
JUEL-4091
Yarim, Cuma; Daybelge, Umur; Nicolai, Albert
Modelling of Rotating Plasma States and their Stability Accounting for Neutral Beam Injection and Helical Perturbations
56 S., 2003
The revisited neoclassical transport theory for a collisional edge layer with steep radial
gradients in the toroidal damping time scale is extended, to include the faster poloidal
damping time scale. The evolution of the toroidal and poloidal rotation speeds is
determined within the frame of neoclassical theory by two equations accounting for
ambipolarity and momentum conservation . The timescales τT and τP for the evolution of
toroidal, UT, and poloidal, UP, velocities are quite different and allow for an expansion
with respect to τP/τT. The truncation of the expansion at the linear term, i.e., UT=UT0+UT1,
and UP= UP0+ UPl, yields four equations for UTO,1 and UP0,1 : A diffusion equation for UT0,
an ordinary differential equation for UP0,1 depending on the UTO-profile, an evolution
equation for UT1 depending on the UP0-profile are obtained by separating the secular parts
from the fast varying parts. Resorting to TEXTOR-data and assuming in a first step a
stationary profile for UT0 the time evolution of UP0 is computed, in particular it is shown
that the UP0 is, in general, close to its neoclassical value, but has the characteristic
deviations at the boundary as demanded by the revisited neoclassical theory . In order to
determine the stability behavior of poloidal and toroidal rotations in a tokamak plasma, the
dependence of the poloidal velocity on time and initial velocity is analysed. It is observed,
that the poloidal and toroidal spin-up tendencies are strongly coupled by nonlocal
interactions, although these evolve essentially on different time scales. Rotation speeds are
also influenced by charge exchange interactions, neutral beam injection, or a radial
polarization current .
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