Work during the current long shutdown (LS1) of CERN’s accelerator complex is making good progress since starting in February this year. Of the LHC’s 1232 dipoles, 15 are being replaced together with three quadrupole-magnet assemblies. By the beginning of September, all of the replacement magnets had been installed in their correct positions and were awaiting reconnection.
Moving the heavy magnets requires specially adapted cranes and trailers. Moreover, there is only one access shaft – made for the purpose during the installation phase – that is wide enough to lower dipoles, each 15 m long and weighing 35 tonnes, to the tunnel. Underground, a specialized trailer carried the replacement magnets to where they were needed. Sensors fitted below the trailer enabled it to “read” and follow a white line along the tunnel floor.
Back in April, the first Superconducting Magnets and Circuits Consolidation (SMACC) teams began work in the tunnel. They are responsible for opening the interconnects between the magnets to lay the groundwork for the series of operations needed for the consolidation effort on the magnet circuits.
The cables of superconductor that form the LHC’s superconducting dipoles and quadrupoles carry a current of up to 11,850 A. The SMACC project was launched in 2009 to avoid the serious consequences of electric arcs that could arise from discontinuities in the splices between the busbars of adjacent magnets (CERN Courier September 2010 p27). The main objective is to install a shunt – a small copper plate that is 50 mm long, 15 mm wide and 3 mm thick – on each splice, straddling the main electrical connection and the busbars of the neighbouring magnets. Should a quench occur in the superconducting cable, the current will pass through the copper part, which must therefore provide an unbroken path. In total, more than 27,000 shunts will have to be put in place – an average of one every three minutes for the teams of technicians, who work on a number of interconnects in parallel.
By the end of summer, three quarters of the interconnect bellows between magnets had been opened. Almost all of the SMACC consolidation activities had been completed in sector 5-6 and the first bellows were being closed again ready for testing. In sector 6-7, the installation of the shunts was being completed and the procedure was starting in sector 7-8. The aim is for completion of the task in July 2014.
