Conceptual design of a visible spectroscopy diagnostic for DTT

The project of the diagnostics for the Zeff radial profile measurement and for the divertor visible imaging spectroscopy, designed for the new tokamak DDT (Divertor Tokamak Test), is presented. To deal with the geometrical and functional constrains of DTT and to minimize the diagnostics occupancy inside the access pipe, an integrated and compact solution hosting the two systems has been proposed. The Zeff radial profile will be evaluated from the Bremsstrahlung radiation measurement (in a wavelength region free of line emissions) in the visible spectral range acquiring emission from the upper part of the poloidal plan (from the equatorial line up to the separatrix). The plasma emission will be focused on optical fibers which will carry it to the spectroscopy laboratory; one more toroidal line of sight crossing the plasma center and laying on the equatorial plane will measure the averaged Zeff on a longer path. The divertor imaging system is designed to measure impurity and main gas influxes, to monitor the plasma position and kinetics of impurities, to follow the plasma detachment evolution. The project aims to obtain the maximum divertor region coverage and to set instruments outside the torus hall, in order to share light among different spectrometers and interferential filter devices and easily change their setup. The system is composed by two mirrors inside a protective head, which protrudes from the diagnostic box where the divertor image transfer optics and the Zeff telescopes are collocated.