Experimental demonstration of an up-down asymmetry effect on intrinsic rotation in the TCV tokamak

Abstract

A new mechanism has recently been proposed that generates a radial flux of parallel momentum in toroidal plasmas. Namely, by considering up-down asymmetric flux surfaces, the symmetry following the magnetic field can be broken and an additional contribution to the turbulent momentum flux arises, potentially changing the intrinsic rotation profile. These predictions are tested with specific experiments on TCV. The intrinsic toroidal rotation is observed to change by roughly a factor of two when changing the up-down asymmetry of the plasma. More precisely, the toroidal rotation gradient changes in the outer part of the plasma, where the flux surface asymmetry is the highest. The experiments were performed for all combinations of the toroidal magnetic field and plasma current directions, that affect the sign of the predicted up-down asymmetry flux. In each case the variation of the intrinsic rotation profile with the up-down asymmetry is observed in the direction predicted by the theory.

Magnetohydrodynamically generated velocities in confined plasma

“…This quantity increases with the viscous Lundquist number. This up-down symmetry effect is in agreement with timeindependent computations [11] and also with gyrokinetic simulations and experiments [19,20]. Fig.…”

Progress and scientific results in the TCV tokamak

“…As the flux is predicted to change sign with either the magnetic field or the plasma current, two specular shapes were created with both signs of each quantity. The intrinsic toroidal rotation speed was indeed observed to change by a factor of two between the two shapes, most of the difference in the gradient being localized in the more asymmetric edge region ( figure 7(b)); the field and current reversals produced results in accordance with the theoretical predictions [36,37].…”

Particle and Momentum Transport in Tokamak Plasmas, the Complicated Path towards the Experimental Validation of the Theoretical Predictions of Transport in Fusion Plasmas

“…The theoretical predictions for this specific (geometrical) symmetry breaking mechanism have been validated against a set of experiments performed in the TCV tokamak, where the flexibility in magnetic configurations has allowed to test all possible combinations in signs of current, field, and up-down reversal of the magnetic configuration, which are theoretically expected to change the sign of the residual stress. A complete consistency between theoretical predictions and experimental observations has been found [99,100], This provides another example of a very clean validation of a specific theoretically predicted mechanism.…”