Interplay between toroidal rotation and flow shear in turbulence stabilisation

• Published in: Physics of plasmas 2016-02, Vol.23 (2)
• Main Authors: Camenen, Y., Casson, F. J., Manas, P., Peeters, A. G.
• Format: Article
• Language: English
• Subjects: Computational fluid dynamics; Computer simulation; Fluid flow; Heat flux; Heat transfer; Parallel flow; Physics; Plasma Physics; Rotation; Shear flow; Tokamak devices; Turbulence; Turbulent flow
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.4942422

The interplay between toroidal rotation u, parallel flow shear u′, and perpendicular flow shear γE in the stabilisation of tokamak turbulence is investigated in non-linear flux-tube gyrokinetic simulations. The simulations are performed for a reference L-mode DIII-D plasma (the so-called shortfall case) at r / a = 0.8 , varying the flow parameters around their nominal values. Depending on the respective signs of u, u′, and γE , turbulence is found to be enhanced, reduced, or unchanged. When the coupling is favorable, the overall effect on the non-linear heat fluxes can be very large, even at moderate flow values. The ion heat flux is, for instance, decreased by a factor of 3 when the direction of the parallel flow shear is reversed with respect to its nominal value. Even more surprising, keeping u′ and γE at their nominal values, the ion heat flux decreases by more than 50% when the toroidal flow is reversed. The relevance of this mechanism in the experiments which depends on the ability to decouple u, u′, and γE is discussed. The interplay between u and u′ observed in the non-linear simulations qualitatively follows the linear stability results and is interpreted in the frame of a simple fluid model.