This link might enlighten you, also this.
The cryogenic technology chosen for the LHC uses superfluid helium, which has unusually efficient heat transfer properties, allowing kilowatts of refrigeration to be transported over more than a kilometre with a temperature drop of less than 0.1 K. LHC superconducting magnets will sit in a 1.9 K bath of superfluid helium at atmospheric pressure. This bath will be cooled by low pressure liquid helium flowing in heat exchanger tubes threaded along the string of magnets. The LHC cryogenic system is very large as well as very cold. Refrigeration power equivalent to over 140 kW at 4.5 K is distributed around the 27 km ring. To save costs, the four existing LEPII 12 kW, 4.5 K cryoplants will be reused. Their cooling power will be increased by 50% and 1.9 K stages will be added. In all, LHC cryogenics will need 40,000 leak-tight pipe junctions. 12 million litres of liquid nitrogen will be vaporised during the initial cooldown of 31,000 tons of material. The total inventory of liquid helium will be 700,000 litres.
Unfortunately the FAQ page at the CERN page is out of order at the moment and cannot be linked. Here is the LHC machine outreach page.
During normal beam dumps there is controlled quenching, using the systems set up for emergency quenching when there are problems with a magnet. Here is a book on LHC like magnet design.