"Drift" instabilities distorting the magnetic surfaces of Tokamak-type toroidal systems

The author draws attention to the fact that the theory of "drift" instabilities of toroidal systems has hitherto made no allowance for the type of instability associated with Alfvén waves. The presence of this type of instability is demonstrated for the case of an axisymmetric Tokamak with circular cross-section. A general method is developed for investigating Alfvén type instabilities and it is shown that the problem is essentially one of finding the "non-hydromagnetic" part of the perturbed plasma pressure. This kind of general approach is used for analysing plasma perturbations in conditions where the influence of finite conductivity and trapped particles is insignificant. It is shown that these perturbations can increase with time, if the plasma temperature gradient is non-zero. The perturbations investigated involve electrons and ions being displaced radially at an almost equal rate, so that the instabilities considered should lead not only to increased thermal conductivity but also to increased diffusion.