Comparing TCV experimental VDE responses with DINA code simulations

Abstract

The DINA free-boundary equilibrium simulation codehas been implemented for TCV, including the full TCV feedback anddiagnostic systems. First results showed good agreement with control coilperturbations and correctly reproduced certain non-linear features in theexperimental measurements. The latest DINA codesimulations, presented in this paper, exploit discharges with differentcross-sectional shapes and different vertical instability growth rateswhich were subjected to controlled vertical displacement events (VDEs),extending previous work with the DINA code on the DIII-Dtokamak. The height of the TCV vessel allows observationof the non-linear evolution of the VDE growth rate as regions of differentvertical field decay index are crossed. The verticalmovement of the plasma is found to be well modelled. For most experiments,DINA reproduces the S-shape of the vertical displacement in TCV withexcellent precision. This behaviour cannot be modelled using lineartime-independent models because of the predominant exponential shape dueto the unstable pole of any linear time-independent model. The other mostcommon equilibrium parameters like the plasma current Ip, theelongation κ, the triangularity δ, the safety factor q,the ratio between the averaged plasma kinetic pressure and the pressure ofthe poloidal magnetic field at the edge of the plasma βp, and theinternal self inductance li also show acceptable agreement. Theevolution of the growth rate γ is estimated and compared with theevolution of the closed-loop growth rate calculated with the RZIP linearmodel, confirming the origin of the observed behaviour.