An experimental study in plasma rotation and momentum transport was carried
out at JET. The toroidal rotation profile was found to scale approximately with
that of the ion temperature. However, significant deviations from this were
found in high density ELMy H-mode discharges, which had broader rotation
profiles. Arotation database analysis showed the variation of the dimensionless
Mach number with respect to the plasma scenario. For predominantly NBI
heated discharges the Mach number was found to be in the range of 0.3–0.45.
Larger Mach numbers were observed in type I ELMy H-modes, while scenarios
exhibiting type III ELMs or L-mode had lower Mach numbers. Advanced
scenarios often showed a significant increase in the central Mach number when
an internal transport barrier formed. A detailed study was done to investigate
the Prandtl number, Pr , defined as the ratio between momentum and ion heat
diffusivity. Generally the Prandtl number was found to be significantly below
unity, e.g. 0.18 < Pr < 0.35. Although it is often predicted that momentum
and heat diffusivity are equal in ITG dominated plasma, also for high density
ELMy H-mode discharges with temperature profiles close and above the ITG
threshold, the Prandtl number was Pr ∼ 0.3. |