  Microwave interferometer in the Limiter Shadow (MILS) is a new diagnostic,
installed on ASDEX Upgrade for electron density measurements in the far
Scrape-Off Layer (SOL). At the chosen frequency of 47 GHz the region of
measurements varies within several centimeters before and after the limiter,
depending on the density. 200 kHz data acquisition allows resolving transient
events such as edge localised modes (ELMs) filaments and turbulence filaments.
The measured quantities, phase shift and power decay of the microwave beam,
which crosses the plasma, are directly connected to the density and do not
depend on any other plasma quantity. In this work, we analyse the influence of
a filamentary perturbation on MILS signals. Simple representation of a filament
is adopted, with parameters relevant to experimental filament properties,
reported for ASDEX Upgrade. Forward modelling is done in COMSOL software by
using RAPLICASOL, to study the response of the MILS synthetic diagnostic to the
presence of a filament. Qualitative and quantitative dependencies are obtained
and the boundaries of MILS sensitivity to filaments, or to the density
perturbation in far SOL in general, are outlined.
