Error field correction in reversed field pinch with feedback stabilization of resistive wall mode

Abstract A recently developed, model-based linear-quadratic optimal resistive wall mode (RWM) control algorithm is extended in this work to include error field (EF) correction. The EF correction is based on a scheme known in control engineering as disturbance estimation and rejection. The new control algorithm performs real-time EF estimation and feedforward EF compensation in parallel with feedback stabilization. The new RWM control algorithm is implemented and tested in reversed field pinch (RFP) plasma experiments on the EXTRAP T2R device. The EF correction leads to improved performance of the RFP plasma, indicated by lower plasma resistance and sustained, less perturbed intrinsic tearing mode rotation, visible as a reduction of the temporal fluctuations in the mode rotation frequency. The estimated spatial and temporal structure of the EF provides useful information for identification of the EF sources in the EXTRAP T2R device.