Design of the motional Stark effect diagnostic in FTU

This article reports on the design of the motional Stark effect diagnostic (MSE) for the Frascati Tokamak Upgrade tokamak (R-maj = 93 cm, r(min) = 33 cm, B-T < 8 T). The attenuation and emissivity of a diagnostic hydrogen bea m have been estimated for typical discharges to assess the feasibility of t he diagnostic. Due to the geometrical constraints the beam direction and th e polarimeter lines of sight lie on a vertical plane on the same horizontal port. This layout has the advantage of a more convenient projection of the polarization vector on the line of sight, which increases the sensitivity of the measure. The relay optics has been designed so as to minimize Farada y rotation effects which would perturb the measurements. Two polarimeters b ased on different modulating techniques are compared and discussed. The fir st one makes use of photoelastic modulators. The second employs a fast rota ting retarder plate. (C) 2001 American Institute of Physics.