Abstract
Sheared toroidal flows can cause bifurcations to zero-turbulent-transport states in tokamak plasmas. The maximum temperature gradients that can be reached are limited by subcritical turbulence driven by the parallel velocity gradient. Here it is shown that (magnetic field pitch/inverse aspect ratio) is a critical control parameter for sheared tokamak turbulence. By reducing , far higher temperature gradients can be achieved without triggering turbulence, in some instances comparable to those found experimentally in transport barriers. The zero-turbulence manifold is mapped out, in the zero-magnetic-shear limit, over the parameter space (, , ), where is the perpendicular flow shear and is the normalized inverse temperature gradient scale. The extent to which it can be constructed from linear theory is discussed.
- Received 28 March 2012
DOI:https://doi.org/10.1103/PhysRevLett.109.265001
© 2012 American Physical Society