JET Rotation Experiments towards the Capability to Predict the Toroidal Rotation Profile

The existence of an inward momentum pinch in JET plasmas was reported in the last IAEA meeting. Since then, several parametric scans to study the size of the inward momentum pinch demonstrate very robustly that the pinch number Rν_pinch/χ_φ in H-mode plasmas is between 3-5 at r/a=0.4-0.8.

Only in plasmas with R/L_n > 3, larger Rν_pinch/χ_φ > 5 are found while other parametric dependencies are weaker. The Prandtl number is not found to depend very strongly on any of the parameters scanned, the values being typically between 1.5 and 2 at mid-radius. In intrinsic rotation studies, toroidal magnetic field ripple was found to affect both the edge rotation by lowering it typically close to zero or to small counter-rotation values and also core rotation where it is counter-rotating.

An experiment to study Mode Conversion Flow Drive was performed using He³ ICRH scheme. Large central counter-rotation up to ν_φ = - 30 km/s was observed at He³ concentration levels of 10-17%, the rotation being proportional to ICRH power. A strong toroidal rotation braking has been observed in plasmas with application of an n = 1 magnetic perturbation field.

The inferred torque has a global profile and originates from non-resonant components. Two types of edge rotation sinks have been analysed using recent JET data. Firstly, ELMs have been found to consistently cause a larger drop in momentum in comparison with the energy loss. Secondly, a difference in the magnitude of momentum and energy losses created by multiple charge-exchange reactions between neutrals and ions is observed, and with a significantly larger reduction in momentum than in energy content.

While it seems probable that rotation profiles will be peaked in ITER thanks to the robust pinch term, its absolute value is still very challenging to predict with the present knowledge of sources and sinks and also due to the uncertainties in the rotation around the plasma edge.