Momentum transport studies in JET H-mode discharges with an enhanced toroidal field ripple

In this study, enhancement of the toroidal field (TF) ripple has been used as a tool in order to reveal the impact of the momentum pinch on the rotation profiles in H-mode JET discharges. The analysis showed that flatter rotation profiles were obtained in discharges with a high TF ripple, attributed to a smaller inward momentum convection. An average inward momentum pinch of approximately V_p ≈ 3.4 m s⁻¹ and a normalized pinch value of RV_p/χ ≈ 6.6 could explain the observation. The data show that the momentum at the edge affects the peaking of the rotation and momentum density profiles. Under the assumption that the heat and momentum diffusivities are equal, an estimate of the levels of the momentum pinch in all discharges in the JET rotation database was made. For H-mode discharge these ranged from 0.3 m s⁻¹ < V_p < 17 m s⁻¹, with 2 < RV_p/χ < 10. A larger momentum pinch was found in discharges with a smaller density profile gradient length, i.e. a more peaked density profile.