  The scattering of lower hybrid (LH) waves due to scrape-off layer (SOL)
filaments is investigated. It is revealed that scattering can account for the
LH spectral gap without any ad hoc modification to the wave-spectrum. This is
shown using a multiscale simulation approach which allows, for the first time,
the inclusion of full-wave scattering physics in ray-tracing/Fokker-Planck
calculations. In this approach, full-wave scattering probabilities are
calculated for a wave interacting with a statistical ensemble of filaments.
These probabilities are coupled to ray-tracing equations using radiative
transfer (RT) theory. This allows the modeling of scattering along the entire
ray-trajectory, which can be important in the multi-pass regime. Simulations
are conducted for lower hybrid current drive (LHCD) in Alcator C-Mod, resulting
in excellent agreement with experimental current and hard X-ray (HXR) profiles.
A region in filament parameter space is identified in which the impact of
scattering on LHCD is saturated. Such a state coincides with experimental LHCD
measurements, suggesting saturation indeed occurs in C-Mod, and therefore the
exact statistical properties of the filaments are not important.
