Cryostats, Applications with Helium, Superconducting Systems, Liquid-Hydrogen Facilities

Cryostats und cryogenic facilites are faced special challenges as the suitability of materials and certain design aspects. A key factor is their leakage ightness. In particular, leakages might occur only at low-temperature conditions or even in contact with superfluidic helium. These can be detected based on cryogenic experience.

Tightness tests of cryogenic facilities are essential in order to enable stable conditions of insulating vacua. In most cases, helium leak tests are employed. They may be challenging even at room temperature if factors such as outgassing, permeation, or virtual leaks occur. In the cryogenic range, this becomes more and more important since material properties can change and diferential-contraction behaviour can occur. Thus, structures which are tight at rom temperature, may feature so-called cold leakages which are hampering the operation at target conditions.

In order to evaluate such damages and to identify their reason, beneath the know-how in the mentiones subject matter especially experience in cryostat design is required. For example, insufficient sealing materials or design implementations may be responsibel.

Superfluid leakages are one more cryogenic feature which may occur in helium facilities below 2.17 K, at lowered helium pressure. The so-called helium-II phase is distinguished by a vanishing viscosity. Thus, it may wet cryocenically cold device structures at a long distance and even escape throug small-sized pores. The ILK Dresden has equipment for such leakage tests available.