Plasma currents induced by resonant magnetic field perturbations in tokamaks

The plasma response on externally applied resonant magnetic field perturbations is studied by means of numerical simulations. It is shown that dependent on collisionality and perturbation strength, plasma currents build up which can compensate the external field. These plasma currents are accompanied by out-of-phase currents and poloidal flows at the resonant surfaces. With an increasing perturbation field the screening of the externally applied field decreases and at a certain level, the vacuum field approximation holds for the total magnetic field.