On-site mirror facet condensation measurements for the Cherenkov Telescope Array

DIPOLD, J.; MEDINA, C.; GARCIA, B; RASZTOCKY, E.; MANCILLA, A.; MAYA, J.; LARRARTE, J.J.; DE SOUZA, V.

NUCLEAR INSTRUMENTS AND METHODS IN PHYSICS RESEARCH A - ACCELERATORS, SPECTROMETERS, DETECTORS AND ASSOCIATED EQUIPAMENT

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 830 p. 407 - 416

0168-9002

P { margin-bottom: 0.21cm; }The Imaging Atmospheric CherenkovTechnique (IACT) has provided very important discoveries in Very HighEnergy (VHE) γ-ray astronomy for the last two decades,being exploited mainly by experiments such as H.E.S.S., MAGIC andVERITAS. The same technique will be used by the next generation ofγ-ray telescopes, Cherenkov Telescope Array ? CTA, whichis conceived to be an Observatory composed by two arraysstrategically placed in both hemispheres, one in the Northern and onein the Southern. Each site will consist of several tens of Cherenkovtelescopes of different sizes and will be equipped with about10000 m2 of reflective surface. Because of its largesize, the reflector of a Cherenkov telescope is composed of manyindividual mirror facets. Cherenkov telescopes operate without anyprotective system from weather conditions therefore it is importantto understand how the reflective surfaces behave under differentenvironmental conditions. This paper describes a study of thebehavior of the mirrors in the presence of water vapor condensation.The operational time of a telescope is reduced by the presence ofcondensation on the mirror surface, therefore, to control and tomonitor the formation of condensation is an important issue for IACTobservatories. We developed a method based on pictures of the mirrorsto identify the areas with water vapor condensation. The method ispresented here and we use it to estimate the time and area twomirrors had condensation when exposed to the environmental conditionsin the Argentinean site. The study presented here shows importantguidelines in the selection procedure of mirror technologies andshows an innovative monitoring tool to be used in future Cherenkovtelescopes.