Summary of the Experimental Studies of Cold Helium Propagation along a scale model of the LHC Tunnel

The Large Hadron Collider will contain more than 95 tons of liquid and supercritical helium. The accelerator will be located in the 26.7 km underground tunnel. Some potential failures of the LHC cryogenic system might be followed by helium discharge into the tunnel and as a consequence the oxygen concentration might decrease below the safe level or the ambient temperature might drop significantly. In order to investigate the helium propagation in the tunnel a dedicated test rig, representing a section of the LHC tunnel at scale 1:13 has been designed and built. The basic construction of the scale model has been also modified by adding special modules to simulate the presence of the LHC accelerator inside the tunnel, tunnel enlargements and the influences of the LHC tunnel elevation. This paper presents and discusses the results of the performed experiments. Helium-air mixture flows corresponding to different initial conditions of the ventilation air and discharged helium have been visualized. Five types of mixture flow have been observed. Measured oxygen concentration and temperature profiles have been presented for the different flow patterns. The results have been scaled to the LHC conditions.