Real time computation of electrodynamic forces on the stabilizing shell from magnetic measurements

This Technical Note describes a method to compute the spatial and time evolution of electrodynamic forces on the passive stabilizing shell during the whole plasma dischargeincluding fast transient phenomena (such as disruptions)by analysing a subset of the availablemagnetic measurements. Since it has very low-computational requirementsit can be used in real-time to monitor the dynamic loads on the shell during experimental operations or together with some discharge simulation model to estimate possible critical loads during high plasma current scenarios.The method is based on the capabilityof estimating the axisymmetric toroidal currents in the passive structures from magnetic field measurements and therefore therelated radial (and tangential)forces due to the interaction with the existing magnetic field.The toroidal component of the shell current linear density has been determined by the poloidal magnetic fields differences measured by the inner-outer magnetic pick-up coils at 8 different poloidalangles and 2 toroidal sections; then, the signal has been reconstructed by DFT harmonic analysis [1].Themethod has been applied both to real experimental measurements butalso to simulated poloidal magnetic fields provided by ANSYS. In the latter case a comparison of the results in terms of shell current and radial force has been performed TwoRFP plasma dischargeshavebeen used as reference scenariosand the related forces have been computed in two different conditions: with vacuumvessel (RFX-mod) and without vacuum vessel(RFX-mod2).The results of the presented method are in good agreement with those provided byANSYS simulations in all the considered plasma scenarios and machine conditions.