Experimental validation of the thermal performance of the 1.9 K magnet cryostats during the commissioning of the LHC

The LHC machine, at present in the commissioning phase at CERN, is composed of eight 1.9 K superconducting magnet sectors independently operated. Assembled in 8 continuous segments of approximately 2.7 km length each, the HeII cryostats for the 1232 dipoles magnets and 438 Short Straight Sections (housing the quadrupole magnets) were designed to fulfil tight heat load budgets for an affordable large-scale project. The commissioning of the cryogenic system of the first LHC sectors is under way since January 2007 and 5 sectors have now been operated at their nominal temperatures of 1.9 K. An experimental assessment of the thermal performance of the final machine is therefore possible, allowing comparison with design estimates. After a brief description of the layout of the LHC cryostats, and their associated cryogenic and vacuum sectorisations, calorimetric measurements of the heat loads to the 1.9 K magnets and to the cryostat thermal shielding are presented and discussed.