Magnetic islands and chaos induced by heat flow

A theoretical model is presented which treats the problem of confinement degradation in tokamaks with increasing input power. It is shown that, when full account is taken of the magnetic field line topology, the adiabatic invariance conditions and the particle motion equations in the guiding centre approximation permit the heat flow to be related with the level of magnetic perturbation associated with large (M ∼ 15) poloidal mode numbers. It is shown that substantial power can be transported across the plasma by low level magnetic fluctuations. One possible mechanism for the self-sustainment of the magnetic islands is investigated. (author)