Oh my, John, I had a feeling someone would ask. So this old liberal arts major turned to the web and found lots of answers. However, I could read very little of them. Here's one that I could kind of understand:
The largest vacuum system in the world
With a total of 104 kilometres of piping under vacuum, the vacuum system of the LHC is among the largest in the world. The insulating vacuum, equivalent to some 10-6mbar, is made up of an impressive 50 km of piping, with a combined volume of 15,000 cubic metres, more than enough to fill the nave of a cathedral. Building this vacuum system required more than 250,000 welded joints and 18,000 vacuum seals. The remaining 54 km of pipes under vacuum are the beam pipes, through which the LHC's two beams travel. The pressure in these pipes is in the order of 10-10 to 10-11mbar, a vacuum almost as rarefied as that found on the surface of the Moon. The LHC’s vacuum systems are fitted with 170 Bayard-Alpert ionisation gauges and 1084 Pirani and Penning gauges to monitor the vacuum pressure.
A vacuum thinner than the interstellar void
Ultra-high vacuum is needed for the pipes in which particle beams travel. This includes 48 km of arc sections, kept at 1.9 K, and 6 km of straight sections, kept at room temperature, where beam-control systems and the insertion regions for the experiments are located.
In the arcs, the ultra-high vacuum is maintained by cryogenic pumping of 9000 cubic metres of gas. As the beam pipes are cooled to extremely low temperatures, the gases condense and adhere to the walls of the beam pipe by adsorption. Just under two weeks of pumping are required to bring the pressures down below 1.013 × 10-10mbar (or 10-13atmospheres).
Two important design features maintain the ultra-high vacuum in the room-temperature sections. Firstly, these sections make widespread use of a non-evaporable "getter coating" – developed and industrialized at CERN – that absorbs residual molecules when heated. The coating consists of a thin liner of titanium-zirconium-vanadium alloy deposited inside the beam pipes. It acts as a distributed pumping system, effective for removing all gases except methane and the noble gases. These residual gases are removed by the 780 ion pumps.
Secondly, the room-temperature sections allow "bakeout" of all components at 300°C. Bakeout is a procedure in which the vacuum chambers are heated from the outside in order to improve the quality of the vacuum. This operation needs to be performed at regular intervals to keep the vacuum at the desired low pressure.
Though these technologies were developed for fundamental research, they have found everyday uses: ultra-high vacuum technology made possible a major improvement in the performance of solar thermal collector panels, for example.
@d-m-holcombe I gotta be honest with you David.....I`m not reading about ANYTHING here that would discourage your typical cat from enjoying this chamber
seriously tho,thank you for the wealth of detailed information on this behemoth
