Fast-wave heating of a toroidal plasma near the ion cyclotron frequency

The absorption coefficient of the magnetosonic wave at the ion cyclotron resonance is evaluated, in the limit of rare collisions, for a toroidal plasma with due allowance for the effect of the rotational transform. It is found that, when the parallel wave number kz imposed by the external coupling structure is small, the power absorption is much larger than that previously evaluated; it is independent of kz and does not vanish, as in a uniform magnetic field, for kz = 0. The plasma loading of an external coupling structure and the radial dependence of the absorbed power are evaluated. A critical radius above which the toroidal modes overlap, allowing for a small Q-value of the launching structure over a wide density range, is deduced.