Experience with the String2 Cryogenic Instrumentation and Control System

String2 was a 120 m full-scale model of a regular cell of the LHC accelerator arc. It was composed of eight superconducting main magnets, fed by a separate cryogenic distribution line (QRL); an electrical feed box (DFB) which supported the superconducting current leads that powered the magnets [1]. Bearing an intensive experimental programme, String2 was heavily instrumented. The cryogenic instrumentation and control system, whose complexity was close to a full 3.3 km LHC sector, have already been described in [2]. String2 was a useful facility to validate design choices and to gain knowledge on installation and commissioning procedures. This paper reports on the experience of four years of designing, installation, commissioning and maintenance, and outlines the lessons learned for the LHC.