Flux surface averaging of the diffusion coefficient in electron cyclotron resonance heating

The single particle model has been used to describe electron cyclotron resonance heating. Fielding's (1980) method of calculating the diffusion coefficient has been simplified and extended to include the effect of finite beam width. It is shown how this effect and the effect of the rotational transform lead to a spreading of the resonance over a wider class of particles and how the diffusion coefficient should be averaged over a magnetic surface or surfaces. (author)