The LHC cryogenic systems are divided into 8 equivalent cryoplants around the LHC ring and each of them supply helium to superconducting magnets over 3.3 km via a cryogenic distribution line (called QRL) installed underground in parallel to magnets.
The Cryogenic Distribution Line inside the LHC tunnel before installation of magnets in parallel
The QRL contains different headers to supply and recover helium from magnets. The header B of the QRL is the pumping line where gaseous cold helium (around 3 K) is pumped by cold compressors at 16 mbar in order to maintain LHC superconducting magnets at 1.8 K. The helium flow inside this pumping line has been modeled to simulate LHC 1.8 K refrigeration units.
When a quench is provoked on a magnet (transition between a superconductor state to a resistive state), an important heat flux is induced in cryogenic line and generates a heat wave through the line. Here, you can see the result of a dynamic simulation of the heat propagation though the header B of the LHC cryogenic distribution line over more than 3 km just after a quench :
B. Bradu, P. Gayet, S.I. Niculescu and E. Witrant.Modeling of the very low pressure helium flow in the LHC Cryogenic Distribution Line after a quench. Cryogenics, In press, 2010.