A cryogen is any fluid that operates at cryogenic temperatures (below around 150K to 120K). By this definition, helium at 40K is a cryogen. A cryogen-free system (also known as a DRY system) is one that provides cryogenic cooling without the use of cryogenic liquids such as liquid nitrogen or liquid helium. Cooling of cryogen-free systems is done using a coldhead to reduce the temperature and liquify Helium to 4K. Pumping to reduce the pressure on the Helium allows further cooling to sub 1K temperatures.
Cryogen-free systems have a number of advantages. They are often smaller in size and weight than systems using liquid reservoirs. They eliminate the effort, training and equipment required for the purchase and use of expensive cryogenic liquids. Safety issues associated with venting the cryogen vapour boil-off are, for the most part, eliminated. These system advantages are valuable where the cryogen is used as a tool rather than the main study focus, for example material or medical research. Extensive training in cryogenics is not required for these systems which allows researchers to concentrate on their main subject matter. Cryogen-free systems remove the challenge of dealing with liquids and boil-off venting in zero gravity in space applications. As a result, the mission lifetime is determined by the reliability of the cryocooler and not the volume of cryogen sent into space.
Cryogen-free systems do have some disadvantages. The systems require power and other services for the cryocooler e.g. pumps. The absence of a liquid bath may make heat sinking more difficult. In the event of a cryocooler failure or power loss, there will be no hold time like that associated with a liquid reservoir before the system warms.
ICEoxford produce cryogen-free superconducting magnets and systems. Many research institutions have benefitted from our expert knowledge and reliable systems.