The sensitivity of the stability of the ideal n = 1 internal kink mode is analysed both analytically and numerically in rotating tokamak plasmas. These stability analyses have been carried out including the centrifugal effects of toroidal plasma rotation upon the equilibrium, and also inconsistently when the equilibrium is treated as static. The plasma stability is partially (consistent equilibrium) or wholly (inconsistent treatment) determined by the radial profiles of the plasma density and rotation velocity. It is found that the internal kink mode stability is strongly influenced by small variations in these plasma profiles. Indeed, modest perturbations to the profiles inside the q = 1 surface of only a few percent can result in a stabilising effect upon the kink mode with respect to the static mode growth rate becoming a destabilising effect at the same rotation amplitude, or vice versa. The implications of this extreme sensitivity are discussed, with particular reference to experimental data from MAST.

An extensive database to study the scaling of rotation and momentum transport has been constructed at JET. The database contains information from various operational scenarios, amongst them H-mode discharges, and parameters that characterize the rotation, as well as those that describe the general plasma conditions. JET plasmas are predominantly heated by neutral beam injection which is also the main source for the observed toroidal rotation. Dimensionless Mach numbers are introduced to quantify rotation. The scaling of plasma rotation and the Mach numbers in particular has been studied. The thermal and Alfvén Mach numbers were found to scale inversely with q and with the ratio of torque and additional heating power. Although the momentum and energy confinement times were found to be of the same magnitude, the ratio was found to vary. Regression analyses showed a dependence of both the energy and momentum confinement times on plasma rotation. If rotation was included in the scaling model of energy and momentum confinement the quality of the fits substantially improved. Detailed analysis of the core and edge (pedestal) confinement showed that momentum confinement was improved in the core of the plasma compared with the energy confinement. However, the pedestal proved to be less confining for the momentum than for the energy.