Abstract
A RICH detector was built in the NA62 experiment to separate pions from muons for particle momenta between 15 and 35 GeV/c. The NA62 experiment was commissioned in 2014 and 2015 and took data in the years 2016, 2017 and 2018. The NA62 RICH consists of a steel vacuum-tight cylindrical vessel, about 17 m long and 4 m wide, enclosing a central beam pipe, filled with neon gas. The Cherenkov light is reflected by a mosaic of 20 spherical mirrors with 17 m focal length, placed at the downstream end of the vessel, and it is collected by 1952 Hamamatsu R7400-U03 photomultipliers (PM) placed at the upstream end. A detailed description of the detector and of its performance during the data taking period are presented.