Vertical position control in TCV: Comparison of model predictions with experimental results

Abstract

Growth rates of the axisymmetric instability of elongatedplasmas in TCV are measured, in open loop configuration, for awide variety of plasma shapes with elongations and triangularities inthe ranges 1.3 < κ < 2.2 and -0.3 < δ < 0.6, respectively,and for stability margins covering the range 1.03 < f < 1.60. In addition,the stability of the vertical position control system is investigatedexperimentally, under closed loop conditions, by varying the feedbackgains and by measuring the oscillation frequencies close to the stability limit. The results of these measurements are compared with theoretical calculations, based on a rigid plasma model (RPM) and on a deformable plasma model (DPM). While RPM underestimates the open loop growth rate for largevalues of δ and overestimates the size of the stabledomain in gain space, DPM gives very good agreement with theexperimental results.