  Electromagnetic wave scattering off density inhomogeneities in the solar
corona is an important process which determines both the apparent source size
and the time profile of radio bursts observed at 1 AU. Here we model the
scattering process using a Fokker-Planck equation and apply this formalism to
several regimes of interest. In the first regime the density fluctuations are
considered quasi-static and diffusion in wavevector space is dominated by
angular diffusion on the surface of a constant energy sphere. In the
small-angle ("pencil beam") approximation, this diffusion further occurs over a
small solid angle in wavevector space. The second regime corresponds to a much
later time, by which scattering has rendered the photon distribution
near-isotropic resulting in a spatial diffusion of the radiation. The third
regime involves time-dependent fluctuations and, therefore, Fermi acceleration
of photons. Combined, these results provide a comprehensive theoretical
framework within which to understand several important features of propagation
of radio burst waves in the solar corona: emitted photons are accelerated in a
relatively small inner region and then diffuse outwards to larger distances. En
route, angular diffusion results both in source sizes which are substantially
larger than the intrinsic source, and in observed intensity-versus-time
profiles that are asymmetric, with a sharp rise and an exponential decay. Both
of these features are consistent with observations of solar radio bursts.
