Numerical analysis of the spectral broadening of the EC resonance for Gaussian beams propagating in inhomogeneous plasmas, with applications to EC H&CD in ITER

A model is proposed which accounts for the modification in the electron cyclotron (EC) resonance condition for Gaussian beams injected in inhomogeneous plasmas, due to the finite width of the transversal spectrum caused by the paraxial character of the beams, within the framework of the complex geometrical optics. The resonance modification due to the non-uniformity of the equilibrium magnetic field is taken into account as well. This model, which is suitable for electron cyclotron resonance heating and current drive applications, has been implemented as an option in the beam-tracing code GRAY. Numerical examples of the application of this new tool to International Thermonuclear Experimental Reactor scenarios are given, with results that indicate a minor effect of the EC resonance broadening on the EC power deposition profiles for the considered cases.