Prediction of the growth rates of VDEs in JET

In this paper we show that the effect of the saddle currents in the rigid sectors slows down the vertical instability of JET elongated plasmas with respect to estimates based on pure axisymmetric models. This, together with an accurate description of the passive structures, significantly improves the agreement between the theoretical predictions and the experimental results. Linearized models taking into account the three-dimensional effects of the eddy currents have been applied to various JET pulses; the growth rates have been estimated within an accuracy of less than 5% for plasmas with a growth time longer than 2 ms. This model can be used for JET and extended to ITER-FEAT to provide a reliable test bed for assessing the performance of the vertical control system and obtain an estimate of the loads on the structures during vertical displacement events (VDEs) and plasma disruptions.