Second sector cool down

At the beginning of July, cool-down is starting in the second LHC sector, sector 4-5.

The cool down of sector 4-5 may occasionally generate mist at Point 4, like that produced last January (photo) during the cool-down of sector 7-8.

Things are getting colder in the LHC. Sector 7-8 has been kept at 1.9 K for three weeks with excellent stability (see Bulletin No. 16-17 of 16 April 2007). The electrical tests in this sector have got opt to a successful start.

At the beginning of July the cryogenic teams started to cool a second sector, sector 4-5. At Point 4 in Echenevex, where one of the LHC’s cryogenic plants is located, preparations for the first phase of the cool-down are underway. During this phase, the sector will first be cooled to 80 K (-193°C), the temperature of liquid nitrogen. As for the first sector, 1200 tonnes of liquid nitrogen will be used for the cool-down. In fact, the nitrogen circulates only at the surface in the heat exchangers of the cryogenic plant. It is used to pre-cool to 80 K the helium that will circulate in the accelerator underground.

During this process, the helium transfers its heat to the nitrogen, which is thereby transformed from a liquid state to a gaseous state before being released into the atmosphere. The nitrogen released into the atmosphere may create mist (see box) around the building housing the cryogenic plant. This phenomenon is absolutely harmless since nitrogen is the primary constituent of the air we breathe. In fact, air consists of 78% nitrogen and 21% oxygen. The phenomenon is generated each time the cryogenics are commissioned in a sector, at points 1.8, 2, 4, 6 and 8 where the cryogenic plants are located.