The first End-Cap Toroid (ECT) for the ATLAS experiment at the LHC has begun the last stage of its journey to the underground cavern. Now that the assembly of the cold mass, integration in the vacuum vessel and connection to the vacuum pumps, cryogenic lines and current leads are all complete, the toroid will undergo a cooling test on the surface before being lowered into the cavern.
The 5 m wide, 11 m diameter, 240 t structure is one of two similar ECTs, the last large magnets to be installed inside ATLAS. Moving at about 1 km/h on a special transport trailer, it left the assembly hall on the Meyrin site in preparation for cold-testing at a nearby outdoor location. The transport operation was extremely delicate: the slightest wrong turn or movement could have caused the tall structure to sway at an angle that would cause serious damage to the fragile parts inside. The toroid cold mass is suspended inside the vacuum vessel by four gravity rods and tipping the ECT at too large an angle could have damaged these rods.
During the surface test, the ECT is being cooled to 80 K using the cryogenic plant in a nearby building. Tests will check for cold leaks in the cooling circuits and verify the electrical insulation of the coils under thermal stress. During the 300–80–300 K thermal cycling, all of the crucial components as well as the magnet’s instrumentation will be thoroughly checked to make sure that it will function properly once installed underground.
The test will last until mid-March. The toroid will then be lowered into the ATLAS cavern in early June for final commissioning, when it will be cooled to 4.5 K using the ATLAS cryogenic plant and charged up to the nominal current of 20.5 kA. The second ECT is scheduled for lowering in early July, just in time for closure of the LHC beam pipe in August.
