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The present status of understanding of toroidal and poloidal momentum transport in tokamaks is presented in this paper. Similar energy confinement and momentum confinement times, i.e. T(E)/T(phi) ~ 1 have been reported on several tokamaks. It is more important though, to study the local transport both in the core and edge plasma separately as, for example, in the core plasma, a large scatter in the ratio of the local effective momentum diffusivity to the ion heat diffusivity X(phi)(eff)/X(i,eff) among different tokamaks can be found. For example, the value of effective Prandtl number is typically around X(phi)(eff)/X(i,eff) ~ 0.2 on JET while still T(E)/T(phi) ~ 1 holds. Perturbative NBI modulation experiments on JET have shown, however, that a Prandtl number X(phi)/X(i) of around 1 is valid if there is an additional, significant inward momentum pinch which is required to explain the amplitude and phase behaviour of the momentum perturbation. The experimental results, i.e. the high Prandtl number and pinch, are in good qualitative and to some extent also in quantitative agreement with linear gyro-kinetic simulations. In contrast to the toroidal momentum transport which is clearly anomalous, the poloidal velocity is usually believed to be neo-classical. However, experimental measurements on JET show that the carbon poloidal velocity can be an order of magnitude above the predicted value by the neo-classical theory within the ITB. These large measured poloidal velocities, employed for example in transport simulations, significantly affect the calculated radial electric field and therefore the E x B flow shear and hence modify and can significantly improve the simulation predictions. Several fluid turbulence codes have been used to identify the mechanism driving the poloidal velocity to such high values.

Additional information

Authors: TALA T et al, Association EURATOM-TEKES, Helsinki University of Technology (FI)
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion 49 B291-B302 (2007)
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