The LHC's main magnets operate at a temperature of 1.9 K (-271.3°C), colder than the 2.7 K (-270.5°C) of outer space. This ensures that the cables supplying power to the magnets operate in a superconducting state; they conduct electricity with no resistance.
The cold magnets are insulated from the surrounding tunnel – kept at room temperature – with multiple layers of thermal insulation.
Over the next 18 months, 1695 interconnections between LHC magnets will be opened and their insulation consolidated. In the video above, narrated by Jean-Philippe Tock of the Technology department, technicians demonstrate the process on an interconnection between spare LHC magnets.
A "W bellows" system slides out of the way to reveal accelerator components inside. The technicians add aluminium sheeting and further insulating material before closing the W bellows for a leak-proof connection. The section is then brought to a pressure of 10-6 mbar, to further limit the possibility of heat leaks from the cold magnets.
Insulating these interconnections is one of many main consolidation activities taking place at CERN during the long shutdown of the accelerator complex.
See diagram: "The main 2013-14 LHC consolidations"