Separation of fluorocarbons in the fluid systems of the DELPHI Barrel RICH detector

Abstract During the run period 1994 the presence of leaks inside the barrel of the DELPHI RICH detector led to an increased mixing of the two fluorocarbon liquids being used as radiator media (gas radiator, C 5 F 12 ; liquid radiator, C 6 F 14 ). To cope with the potential risk of boiling or condensation, as well as with the varying refractive indices, intervention became indispensable. We report on the methods that allowed us not only to monitor and stabilize the respective contaminations, but also to follow the time dependence of the refractive indices. In the run period 1995 the installation of a dedicated on-line separation plant in the gas radiator system combined with an on-line distillation plant in the liquid radiator system maintained the mixing at a level below 20%. In addition, the use of specially designed vapour pressure cells allow a permanent and precise monitoring of the composition and thereby of the refractive indices of the radiator media.