The PLUS ultraviolet spectrograph for the observation of planetary exospheres

Ultraviolet spectographs are of key importance in Solar physics, in the physics of interstellar medium and in the planetary exospheres studies. The best technique to probe the exospheres and the highest-altitude atmospheres of planets and satellites is in fact the FUV/EUV (Far/Extreme Ultraviolet) imaging spectrometry; it allows to determine constituents and dynamics of the atmosphere, to understand its formation mechanisms and surface release processes. This work focuses its attention on the presentation of the most recent Ultraviolet spectograph: PLUS (PLanetary Ultraviolet Spectrometer), and provides the description of two experimental activities related to the project, in which I was actively involved at CNR-IFN laboratory. PLUS is a two channels high performance spectrograph which will be used to observe planetary exospheres in the 55-200 nm range, where there are signifcant spectral features. It is a state of the art scientifc device in the study of planetary exospheres, since it improves the performance thanks to high effciency optical components optimized for each channel and a simplifed design. The frst activity performed at the laboratory is related to the vacuum chamber and the gratings’ mounts inside it, my role has been to start up the controller and understand how to move the gratings’ supports in order to realise the desired alignment. The second activity aimed to obtain the calibration of the slit width with respect to the position of a knob able to change this width. For this purpose, I have extracted the sought value from the diffraction fgure, obtained by illuminating the slit with a laser beam, for three different positions of the knob. The project funding started in 2020 and should last until December 2022, it has been granted within the implementation agreement ASI (Agenzia Spaziale Italiana)-INAF (Istituto Nazionale di AstroFisica) n.2018-16-HH.0 in relation to ”Attivita di Studio per la comunit ` a scientifca nazionale ` SOLE, SISTEMA SOLARE ED ESOPIANETI”, which wants to support the study of Sun, Solar Systems and Exoplanets. Currently, researches from CNR-IFN Padova, INAF/IASF Milano, Politecnico di Milano and University of Padua are working on the PLUS project.