A dilution microcryostat-insert

Abstract

An autonomous dilution microcryostat in which ³He circulates due to its condensation in the volume cooled by sorption evacuation of ³He from a separate bath. A specific feature of this apparatus is the position of the sample holder in its upper part, which facilitates access to it. The holder is connected to the mixer through a heat conductor made from annealed copper wire with a length of ∼0.5 m. The cryostat operates while inserted into a nitrogen-free portable (35 l) helium-filled vessel. The operating cycle of the cryostat includes the procedures of desorption, condensation, and cooling of the ³He-filled bath to 0.35–0.40 K and the mixer to 0.05–0.10 K (lasting ∼1.5–2.0 h) and also a period of maintaining the temperature below 0.1 K (12–14 h). The amount of liquid helium in the portable cryostat is sufficient for operating for 6 days. The lowest reached temperature of the holder is 0.04 K. When the power dissipated in the holder is 0.5 μW, its temperature does not increase above 0.1 K. The instrument is mainly designed for cooling sensitive radiation detectors.