The cryogenics at the LHC

[jmc2000]

Over the past few weeks I've noticed that they might lose between 1/2-1 days on the cyrogenics failing.

How good are the cryogenics at the LHC compared to the Tevatron?

What are the problems with cryogenics upto now and how difficult have they been to fix?

Which part of the tunnel is the least accessible?

[pcatom]

Over the past few weeks I've noticed that they might lose between 1/2-1 days on the cyrogenics failing.

How good are the cryogenics at the LHC compared to the Tevatron?

What are the problems with cryogenics upto now and how difficult have they been to fix?

Which part of the tunnel is the least accessible?

The LHC system is much bigger than the Tevatron. LHC has 8 cryogenic plants - each one is somewhat larger than the complete Tevtron system (41g/s in LHC vs. 35g/s in Tevatron). In addition the LHC has a cold compressor stage in order to cool the magnets to 1.9K which is completely absent in the Tevatron (magnet temperature 3.5K). The LHC cryogenics has to cool around 40,000 tonnes of equipment to 1.9K and has a Helium inventory of around 120 tonnes. The thermodynamics of such a system means that it cannot act rapidly!

The cryo-plants are very dependent on the electrical and cooling services. Any interruption of these (even a short one) means many hours to recover the conditions. Both Tevatron and LHC are in the same situation here.

The actual fault rate of the cryogenics system in the LHC is remarkably small for such a large and complex system.

[jmc2000]

Over the past few weeks I've noticed that they might lose between 1/2-1 days on the cyrogenics failing.

How good are the cryogenics at the LHC compared to the Tevatron?

What are the problems with cryogenics upto now and how difficult have they been to fix?

Which part of the tunnel is the least accessible?

The LHC system is much bigger than the Tevatron. LHC has 8 cryogenic plants - each one is somewhat larger than the complete Tevtron system (41g/s in LHC vs. 35g/s in Tevatron). In addition the LHC has a cold compressor stage in order to cool the magnets to 1.9K which is completely absent in the Tevatron (magnet temperature 3.5K). The LHC cryogenics has to cool around 40,000 tonnes of equipment to 1.9K and has a Helium inventory of around 120 tonnes. The thermodynamics of such a system means that it cannot act rapidly!

The cryo-plants are very dependent on the electrical and cooling services. Any interruption of these (even a short one) means many hours to recover the conditions. Both Tevatron and LHC are in the same situation here.

The actual fault rate of the cryogenics system in the LHC is remarkably small for such a large and complex system.

Wow, With so many things which can go wrong, yet it manages to be relaiable. I suspect that a strategy may be to double up on as many things as possible to make it unlikely that two of the same thing will fail at the same time.