The Divertor Tokamak Test (DTT) facility [1], whose construction is starting in Frascati, will require robust and reliable diagnostics for the correct operation of the machine and the characterization of the plasma discharge. For this purpose, we are studying a common-path dispersion interferometer/polarimeter for the detection of plasma electron density and magnetic field in two different tangential chords in the equatorial plane. The physical principle is based on the generation of a second harmonic which crosses the plasma collinearly with the beam at its fundamental. Being the plasma a dispersive medium, the two beams are subject to different phase shifts from which it is possible to retrieve the plasma free electron density. Moreover, the unconverted part of the fundamental can be used for polarimetric measurement. Two different implementations of the interferometer have been considered, one with a CO2 laser (λ = 10.6/5.3 µm) and another one with Nd:YAG (λ = 1.064/0.536 µm). The former is more sensitive to lower plasma densities and to Faraday rotation, while the latter is more robust to fringe jumps. We have studied the main aspects of these two possible solutions. In particular, we analysed the optics to be used and the expected maximum signals for the interferometry and the polarimetry in a possible plasma scenario of DTT. A tentative draft of the layout of the optics inside the machine will be also presented.

Interferometry is the commonly exploited technique for electron density measurements in magnetically confined fusion plasma experiments. Reliable electron density measurements are fundamental both for machine protection and for plasma physics understanding. In the last years, attention was drawn on the dispersion interferometer concept, because of its robustness and simplicity. Nevertheless, the heterodyne version of this configuration, which has several advantages over the homodyne scheme, loses one of the main benefits of the dispersion interferometer technique, that is its inherent insensitivity to vibration errors. In this paper, two methods are proposed and theoretically investigated to reduce the vibration noise in the electron density measurements performed with heterodyne dispersion interferometers.