Significant progress has been made in interpreting the effects of non-axisymmetric “error” fields on a plasma through ideal MHD stability and a dominant “least stable” ideal mode through which the fields couple to the tearing resonant surface. However, in contrast to expectations from such theories, experiments have found limited success in correcting error fields, with single correction coil arrays giving benefits of between 0% and 50% correction (in terms of improvement to a low density locked mode limit), dependent on the structure of the error and correcting fields. With additional coils up to 70% is possible.
