1. CEA-Grenoble / DSM / DRFMC / Service des Basses Températures / B. rousset1 24/04/2007 LHC cooling scheme magnet 1 bar 4.2 K Pressurized HeII bath Vapour  T2 Liquid Saturated He II bath  T1 A Tore Supra like cooling scheme ? Any instabilities ? Enhance transverse heat transfer by use of corrugated pipe ? Two-phase flow pressure drop compatible with longitudinal DT ?

2. CEA-Grenoble / DSM / DRFMC / Service des Basses Températures / B. rousset2 24/04/2007

3. CEA-Grenoble / DSM / DRFMC / Service des Basses Températures / B. rousset3 24/04/2007 LHC nominal operation Main results concerning pressure drop

4. CEA-Grenoble / DSM / DRFMC / Service des Basses Températures / B. rousset4 24/04/2007 Low vapour velocity No liquid droplets High vapour Velocity Lots of droplets Main results concerning heat transfer LHC nominal operation

5. CEA-Grenoble / DSM / DRFMC / Service des Basses Températures / B. rousset5 24/04/2007 From this results on co-current HeII two-phase flow (no instability for descending co- current two-phase flow, longitudinal and transverse DT small enough to correctly cool down the magnets) we concluded that this cooling scheme will be used to cool down the LHC superconducting magnet strings. For upgrade of LHC, the use of smaller sector with high vapour velocity will also meets the requirement. Conclusion