THE SEPARATRIX RESPONSE OF DIVERTED TCV PLASMAS COMPARED WITH THE PREDICTIONS OF THE CREATE-L MODEL

The response of ohmic, single null diverted (SND), non-centred plasmas in TCV to poloidal field coil stimulation has been compared with the predictions of the linear CREATE-L MHD equilibrium response model. The closed loop responses of directly measured quantities, reconstructed parameters and the reconstructed plasma contour have all been examined . Provided that the plasma position and shape perturbation were small enough for the linearity assumption to hold, agreement between the mod el and experiment was good. For some stimulations the open loop vertic al position instability growth rate changed significantly. This led to oscillations in the vertical position that were unpredicted and illus trated the limitations of a linear model. A different model was develo ped with the assumption that the flux at the plasma boundary is frozen and the predictions of this model were also compared with experimenta l results. It proved not to be as reliable as the CREATE-L model for s ome simulation parameters, showing that the experiments were able to d iscriminate between different plasma response models. The closed loop response was also found to be sensitive to changes in the modelled pla sma shape. It was not possible to invalidate the CREATE-L model, despi te the extensive range of responses excited by the experiments.