The hermetically sealed Thales cryo coolers have a thin walled stainless steel cold finger, in which the displacer is moving with a very small clearance. When the cold finger is at cryogenic temperature (77K) the tube of the cold finger has a temperature gradient from 77 to 300 K. Due to the conductivity of the stainless steel tube, part of the produced cold is destroyed by heat being conducted allong the cold finger wall, to the cold tip. This means that the produced cooling power in the expansion space of the cold finger is reduced.

The cold finger is in the slip-on application integrated into a Dewar bore with a larger diameter than the cold finger and with the cold tip in good thermal contact with the bottom of the bore containing the device to be cooled. Both the conduction by the air between the cold finger and dewar bore and the required thermal interface between the tip of the cold finger and dewar bore, reduce the efficiency of the cooler.

The logical step, to improve efficiency, would be to narrow the dewar bore to such a dimension that it matches the dimensions of the displacer. In that case the stainless steel tube can be removed and the full cooling power available can now be applied to the object to be cooled.

When integrated with the dewar, the cooler and dewar bore have to be purged and filled with dry helium and subsequently closed. In Thales IDCA coolers this is achieved by the use of a combined filling/closure port on the cooler.

Thales Cryogenics provides training to customers, to perform the required purge and filling of the cooler.