Poloidal spin up and electric-field generation related to displacement current and neoclassical transport |
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Authors: | G Gervasini E Lazzaro E Minardi |
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Institution: | (1) Istituto di Fisica del Plasma, Associazione EURATOM-ENEA-CNR, Via Bassini 15, 20133 Milano, Italy |
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Abstract: | Summary In accordance with the conventional orderings of neoclassical theory, poloidal and toroidal accelerations with constant parallel
flow can be driven by heat transport in the absence of external momentum input and with vanishing parallel viscous stress.
In a transient phase in which the heat transport is the primary source of the time dependence, the torque generating the rotation
is provided at third order in the adiabatic expansion by the surface-averaged (non-ambipolar) displacement current, which
is also responsible for charge build-up and for the radial electric field. The heat transport equation has been solved in
a narrow layer interfaced with the intensely heated plasma core through heat flux continuity, assuming neoclassical multicollisional
coefficients with self-consistent suppression mechanism of anomalous transport. Starting from low temperature in the edge
layer, a strong temperature gradient, a mass poloidal rotation in the ion direction and a strongly negative sheared radial
electric field can be generated, in agreement with the observations, and reach a stationary state after a displacement current-dominated
triggering phase (intrinsically non-ambipolar) lasting few milliseconds. Momentum input becomes important on longer time scale
and is responsible for the toroidal rotation, decoupled from temperature gradient and for a further development of the radial
electric field. The results show the ability of edge transport processes to adapt flexibly to a high temperature imposed on
the inner side of the edge layer and support the view that the edge processes are an integral part of a more fundamental global
process involving possibly an internal bifurcation of state. |
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Keywords: | Transport properties |
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