A general solution is proposed to the coupling problem which appears in theoretical studies of the perturbed equilibrium and the plasma stability active control in tokamaks. This is based on the separation of the plasma contribution from the total magnetic field found by solving the perturbed equilibrium problem. A numerical procedure to decouple the components of different origins was developed recently when the plasma code MARS and the electromagnetic code CARIDDI allowing a detailed 3D simulation of the outer region were integrated into the CarMa code (Albanese et al 2008 IEEE Trans. Magn.44 1654, Portone et al2008 Plasma Phys. Control. Fusion50 085004). Here we show that the necessary separation can be described in the explicit form by a single equation, which gives the easiest and direct solution. The analysis is based on the first principles, and the result can be used with any model of the plasma.
The AC response of a tokamak plasma to driven helically resonant radial magnetic perturbations