Closed-loop MIMO ARX estimation of concurrent external plasma response eigenmodes in magnetic confinement fusion

Detailed experimental MIMO models of plasma stability behaviour are becoming increasingly important in magnetic confinement fusion (MCF) energy research as an assortment of magnetohydrodynamic (MHD) instabilities develop when fusion performance is pushed. Some of these problems could perhaps be handled by magnetic feedback. We here show a practical method for experimental closed-loop multi-input multi-output (MIMO) characterisation of the macroscopic stability of toroidal MCF devices. It is demonstrated, by application to the MCF experiment EXTRAP T2R, that MHD eigenmodes can be detected using the workhorse MIMO autoregressive exogeneous (ARX) model structure. Plausibly, the presented methodology could significantly improve highly-desired magnetic feedback accuracy in MCF.