ABSTRACT

The development of commercial “4 K” cryocoolers reached a breaking-through point when the cryocoolers reached the base temperature below 4.2 K (actually it is uncommon to reach below 3 K): the temperature that was previously accessible only by using liquid Helium.

The “4 K” cryocoolers provide temperatures low enough for direct helium condensation.

Examples “4 K Cryogen-free systems” with various types of applications are presented.

Starting from the 4 K platform, lower temperature around 1.5 K can be reached by reducing the liquid helium saturated vapor pressures.

Two types of 1.5 K cryogen-free systems were introduced: Single shot type system and continous flow type (also refered to as recirculating) system which can be operated with longer (or unlimited) holding time.