The effects of applied three-dimensional magnetic error fields on magnetic surfaces are measured in both the Joint European Torus (JET) and the Mega Ampère Spherical Tokamak (MAST). Static perturbation fields with various amplitudes have been applied in both devices using non-axisymmetric coils producing a dominantly n = 1 magnetic field to systematically perturb the plasma flux surfaces. The displacement of the plasma boundary is found to increase linearly with the strength of the applied field, and agrees well with predictive modelling which superimposes vacuum non-axisymmetric fields on a 2D equilibrium.
Controlling the size of non-axisymmetric magnetic footprints using resonant magnetic perturbations