Turbulent momentum transport due to the beating between different tokamak flux surface shaping effects

Abstract

Abstract.Introducing up-down asymmetry into the tokamak magnetic equilibria appears to be a feasible method to drive fast intrinsic toroidal rotation in future large devices. In this paper we investigate how the intrinsic momentum transport generated by up-down asymmetric shaping scales with the mode number of the shaping effects. Making use the gyrokinetic tilting symmetry (Ball et al (2016) Plasma Phys. Control. Fusion 58 045023), we study the effect of envelopes created by the beating of different high-order shaping effects. This reveals that the presence of an envelope can change the scaling of the momentum flux from exponentially small in the limit of large shaping mode number to just polynomially small. This enhancement of the momentum transport requires the envelope to be both up-down asymmetric and have a spatial scale on the order of the minor radius.

Optimized up–down asymmetry to drive fast intrinsic rotation in tokamaks

“…There are two ways to circumvent this restriction. First, we can break tilting sym metry using nonmirror symmetric flux surface shapes [20,21] (i.e. shapes that do not have mirror symmetry about any line in the poloidal plane).…”

Intrinsic rotation driven by turbulent acceleration

“…A comprehensive theory including all of these symmetry-breaking mechanisms is given in [16,17,18,15,19]. There have also been a number of studies dedicated to individual mechanisms, including the effect of diamagnetic flows [20,21,22,23,24], up-down asymmetry of flux surfaces [25,26,27,28,29,30,31,32,33,34], slow poloidal variation of fluctuations [35], and 'global' effects [36,37,38,39], which include radial profile variation mingled with the other effects mentioned. Here we consider the effect of turbulent particle acceleration along the mean magnetic field.…”