Role of symmetry-breaking induced by E_r × B shear flows on developing residual stresses and intrinsic rotation in the TEXTOR tokamak

Direct measurements of residual stress (force) have been executed at the edge of the TEXTOR tokamak using multitip Langmuir and Mach probes, together with counter-current NBI torque to balance the existing toroidal rotation. Substantial residual stress and force have been observed at the plasma boundary, confirming the existence of a finite residual stress as possible mechanisms to drive the intrinsic toroidal rotation. In low-density discharges, the residual stress displays a quasi-linear dependence on the local pressure gradient, consistent with theoretical predictions. At high-density shots the residual stress and torque are strongly suppressed. The results show close correlation between the residual stress and the E_r × B flow shear rate, suggesting a minimum threshold of the E × B flow shear required for the k_∥ symmetry breaking. These findings provide the first experimental evidence of the role of E_r × B sheared flows in the development of residual stresses and intrinsic rotation.