The first sector of CERN's Large Hadron Collider (LHC) to be cooled down has reached a temperature of 1.9 K (‑271°C), colder than deep outer space.
Although it is just 1/8th of the LHC ring, this sector is the world’s largest superconducting installation.
I reported in 2005 the first time about this huge gadget in Switzerland. The entire 27km LHC ring needs to be cooled down to this low temperature in order for the superconducting magnets that guide and focus the proton beams to remain in a superconductive state.
"This is the first major step in the technical validation of a full-scale portion of the LHC," explained LHC project leader Lyndon Evans.
There are three parts to the cool down process, with many tests and intense checking in between. During the first phase, the sector is cooled down to 80 K, slightly above the temperature of liquid nitrogen. At this temperature the material will have seen 90% of the final thermal contraction, a 3 millimeter per meter shrinkage of steel structures. Each of the eight sectors is about 3.3 kilometers long, which means shrinkage of 9.9 meters.
To deal with this amount of shrinkage, specific places have been designed to compensate for it, including expansion bellows for piping elements and cabling with some slack. Tests are done to make sure no hardware breaks as the machinery is cooled.
The 2nd phase brings the sector to 4.5 K using enormous refrigerators. Each sector has its own refrigerator and each of the main magnets is filled with liquid helium, the coolant of choice for the LHC because it is the only element to be in a liquid state at such a low temperature.
The 3rd phase requires a sophisticated pumping system to help bring the pressure down on the boiling Helium and cool the magnets to 1.9 K.
See also this press-release on the CERN site.