New diagnostics for density measurement on Frascati Tokamak upgrade

In FTU, density profile is measured with two new diagnostics: a CO2/CO scanning interferometer and a time-of-flight radar (denominated refractometer). The first, using two scanning beams, can provide a plasma density profile every 62.5 μs. Two lasers (CO2/CO) are employed for compensation of mechanical vibration of optical components. The scanning component is a small mirror (∅=5 mm) tilting at 8 kHz. The oscillation is cancelled out by a second reflection on this mirror. The time-of- flight refractometer is a two-frequency radar (51.5 GHz and 60.5 GHz) which measures the plasma refractive index from the delay time of an RF pulse that goes through the plasma and is reflected back by the metallic vacuum vessel. The line density and the profile peaking by both diagnostics are in good agreement.