A fiber optic sensors monitoring system for the central beam pipe of the CMS experiment

In this paper we describe the main characteristics and experimental results, recorded in more than four years of data acquisition, of a temperature and strain monitoring system, called i-pipe, based on Fiber Bragg Grating (FBG) sensors arrays applied for the first time to a sector of the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN): the central beam pipe (BP) of the Compact Muon Solenoid (CMS). The monitoring system, consisting of four arrays of 16 FBG sensors each, as better described in the text, is placed on four directives of the LHC section that passes inside the CMS experiment, namely the CMS central BP. The mechanical complexity of the central BP structure is described and the monitoring results of its thermal conditions and online unpredictable mechanical deformations are discussed in this paper. In spite of the harsh working conditions this monitoring system is operational since 2015 continuously (24/7) and the data collected are a confirmation of its reliability. This FBG sensors system represents the ideal solution to realize an accurate and robust sensing system to be used in harsh environments, like the CMS experimental facility and all the other High Energy Physics experimental infrastructures.