Magnetic islands and their effects in Tokamak plasmas

A confinement model for tokamak plasmas based on the idea that a number of low mode number magnetic islands appear, grow and interact is described. It is suggested that the fundamental topology of tokamak plasmas is given as a time-varying mix of magnetic islands, magnetic stochasticity and regions with good magnetic surfaces. The presence of magnetic islands in the plasma 'equilibrium' can alter the mode structure and the stability boundaries of ideal ballooning modes in tokamaks. The envisioned magnetic topologies can have an important effect on the understanding and interpretation of observed fluctuations, stability properties and transport characteristics of toroidal confinement devices.