Bifurcated Helical Core Equilibrium States in Tokamaks
Tokamaks with weak to moderate reversed central shear in which the minimum
rotational transform $q_{min}$ is in the neighbourhood of unity can trigger
bifurcated MagnetoHydrodynamic (MHD) equilibrium states, one of which is
similar to a saturated ideal internak kink mode. Peaked prescribed pressure profiles reproduce the ``snake'' structures observed in many tokamaks which has led to a novel explanation of the snake as a bifurcated equilibrium state.Snake equilibrium structures are computed in simulations of the TCV, DIII-D and MAST tokamaks. The internal helical deformations only weakly modulate the plasma-vacuum interface which is more sensitive to ripple and resonant magnetic perturbations. On the other hand, the external perturbations do not alter the helical core deformation in a significant manner. The confinement of fast particles in MAST simulations deteriorate with the amplitude of the helical core distortion. These three-dimensional bifurcated solutions constitute a paradigm shift that motivates the applications of tools developed for stellarator research in tokamak physics investigations.
2012
REVIEWED
Event name | Event place | Event date |
San Diego CA (USA) | 8-13 October 2012 | |