Vertical instability in TCV: Comparison of experimental and theoretical growth rates

Growth rates of the axisymmetric mode in vertically elongated plasmas in the Tokamak a Configuration Variable (TCV) are measured and compared with numerically calculated growth rates for the reconstructed equilibria. This comparison is made over a range of discharge parameters including elongation, triangularity and vertical position within the vacuum vessel. Growth rates increase with respect to increasing elongation, decreasing triangularity and increasing vertical distance from the top of the vacuum vessel, as expected. The agreement between the growth rates measured in the experiment and the numerically determined growth rates is excellent, in particular for the full Linear magnetohydrodynamic (MHD) model, which accounts for the non-rigid motion of strongly shaped plasma cross-sections.