Retro-reflected channels of the Tore Supra FIR interfero-polarimeter for long pulse plasma operation

On Tore Supra, five far infrared (FIR) retro-reflected channels have been installed to double the existing traversing ones, in order to increase the spatial resolution of the electron and current density measured by the interfero-polarimeter diagnostic. w channel geometries are similar to those of the intended ITER polarimeter and have been designed for long pulse plasma operation. Inside the tokamak, the beams are reflected on edge-cooled retro-reflectors. During the 2003–2004 TS campaign, a prototype and reference plan mirrors had been exposed to plasma. After their removals, quantitative SIMS deposit analysis estimate the thickness of the carbon up to 700 nm and FIR measurements confirmed that the surface changes were too small to modify the reflectivity of the mirrors. ansport of the FIR beams by mirrors to the detectors is then discussed. Ray tracings through plasma and mirrors have been done to rightly design and position the windows, the detectors and the separation grids and minimize the misalignment effects. results of both interferometric and polarimetric reflected channel signals show a good consistency with the traversing ones and allow resolving more accurately the profiles.