A cryostat is an apparatus used to maintain very low (“cryogenic” <∼100 K) temperatures. It typically consists of two vessels, one mounted inside of the other. The inner vessel contains the cold sample (cryogen) mounted inside an evacuated outer vessel. The vessels are held together by a material with low thermal conductivity. The vacuum in the outer vessel serves as a thermal insulator. The two vessels are separated by a radiation shield to prevent heat transfer. The radiation shield is cooled by a cryocooler.
In medicine, a cryostat is a device to cut histological slides, consisting of a microtome (ultrathin slicer) in a freezer. In astrobiology, cryostats are used to generate low temperature conditions, for example, for simulating surfaces of icy moons or Titan or even the surface of Mars. Furthermore, studies of ices and chemistry taking place in ices require the use of a cryostat; examples of these are interstellar and cometary ices.