A view on onset and control of magnetic reconnection in tokamak plasmas

Magnetic reconnection is an important process, ubiquitous in space and in laboratory magnetized plasmas. In a tokamak device, helical magnetic field perturbations "tear" the axisymmetric equilibriun configuration growing exponentially on a "tearing" time scale and subsequently evolve into a magnetic island which saturates at a width which produces a minimum in the magnetic energy of the configuration. Large magnetic island may lead to disruptive collapse of the discharge, through phases of thermal quench and current quench.A reliable tokamak reactor operation,on the economically useful time scales, requires the development of strategies to keep under control, and suppress the nonlinear islands growth to avoid disruptions. Here we summarize the state of the art of the problem and of the proposed solutions.