The complexity of the TJ-II magnetic field is patent from the following examples, in which a magnetic field property is mapped onto the last closed flux surface (configuration 100_44_64). The influence of the toroidal field coils is clearly visible (there are 32 toroidal field coils, leading to the striped pattern), as well as that of the circular/helical coils (continuous red stripe in the toroidal direction in the first two figures below).
Absolute value of the magnetic field, |B| (T).
Normal magnetic curvature of the magnetic field, κN. Positive values of κN are regions where curvature-driven modes are expected to be stable (note that this figure corresponds to the vacuum magnetic field -without plasma- so that strictly speaking it is not correct to speak about plasma stability).