Polarization in millimeter-wavelength collective Thomson scattering on FTU tokamak

We investigate performance degradation caused in mm-wave collective Thomson scattering on the high-field tokamak FTU by the joint effects of refraction and polarization. It is shown that optimized performances can be recovered, in different parts of the FTU density range, by selecting the most suitable of the four modal combinations potentially contributing to the scattered signal. This can be achieved by matching the limiting polarization of the selected mode at both the transmitting and the receiving side. A full polarization-control capability is required at this purpose.