Scattering of radio frequency waves by edge density blobs and fluctuations in tokamak plasmas

The density fluctuations and blobs present in the edge region of magnetic fusion devices can scatter radio frequency (RF) waves through refraction and diffraction. This work considers refractive scattering using the geometric optics approximation and canonical perturbation theory. We derive the evolution equation for wave vectors along a ray as it encounters a random distribution of density blobs. It is found that the scattering can diffuse rays in configuration space and in wave-vector space. The diffusion in space can make the rays miss their intended target region, while the diffusion in wave-vector space can broaden the wave spectrum and modify the wave damping profile.