Experimental Investigation of Accidental Loss of Insulation Vacuum in an LHC Prototype Dipole Cryostat

Abstract

A sudden loss of insulation vacuum in an accelerator cryomagnet system be it due to a helium leak from a cryogenic circuit or leak from atmosphere has consequences for the cold mass as well as for the vacuum enclosure. The vacuum enclosure for the LHC dipole cryostat is made of carbon steel to reduce costs and to provide magnetic shielding. In the case of a loss of insulation vacuum the vacuum enclosure will be cooled rapidly but must not reach temperatures low enough to cause embrittlement of the wall material. Helium gas at room temperature was admitted into the insulation space of a modified prototype cryomagnet, the cold mass of which had been previously cooled to 80 K. The evolution of temperature with time of the cold mass and of the vacuum enclosure has been measured and the corresponding heat influx estimated from a simple model.