Modeling of L-mode plasma intrinsic rotation in ASDEX Upgrade

摘要

Introduction Ohmic plasma discharges in tokamaks exhibit a rich phenomenology with complex parameter dependences and present a challenging area for theoretical description. A lot of recent attention has been drawn to the observed in many machines establishment of plasma toroidal rotation in the absence of any external source of momentum. This intrinsic plasma rotation has been found to develop a significant velocity gradient around mid-radius with the increase of collisionality, with high counter-current velocity in the core. However, at even higher collisionality the velocity profile relaxes back to roughly flat. It can be shown that such behavior can only arise from a component of the stress tensor (referred to as the residual stress) not related to either viscosity or convection, which appears when the plasma poloidal symmetry is broken. Many symmetry breaking mechanisms have been proposed recently [1,2]. Several local mechanisms have been tested with AUG parameters and found to be weak [3], hence a global mechanism is believed to dominate. We assume the most prominent global effect to be the finite poloidal tilting of turbulent eddies due to the radial shearing of background equilibrium profiles [4]. This gives rise to a finite poloidally averaged parallel wave number {formula} that generates the residual stress. The main aim of this work is to estimate the tilt angle {formula} values that suffice to explain the observed toroidal rotation profiles assuming the profile shearing is the only symmetry breaking mechanism, though a consequent flow shearing is also accounted for.