Collective Thomson Scattering on FTU using a new ECRH launcher

Different conditions make the CTS diagnostic experiment presently installed at FTU a unique test bed for a proof-of-principle demonstration for a fast ions diagnostic in ITER. The most relevant one is wave propagation at frequencies below the electron cyclotron (EC) resonance where the extraordinary (X) mode can propagate at higher plasma densities. CTS measurements performed in the past with an up-to-down scattering geometry, showed damages on the launching mirror close to the EC resonance located in the port interior. Therefore a different and more flexible CTS geometry was required to achieve a better insight into this difficult problem (found also in the ITER CTS geometry) and to single out a convenient remedy. This opportunity is now offered by the new ECRH launcher that will be installed at FTU. The system has been designed for both ECRH and CTS. It includes two symmetrical lines with front-steerable mirrors and will provide extended focusing capability, independent toroidal and poloidal scans of the probing and the receiving beams, and the possibility of radially scanning, or even changing, the scattering volume during a single gyrotron pulse.