The Kelvin temperature scale is the principal temperature scale used in cryogenics and science. The kelvin is also one of the seven base units in the Système International d’Unités (SI) and is the unit of thermodynamic temperature. Thermodynamic temperature is a fundamental physical quantity (like mass, length or electrical current) and must equal zero at … Continue reading Kelvin Temperature Scale

The Joule-Thomson (JT) effect is a thermodynamic process that occurs when a fluid expands from high pressure to low pressure at constant enthalpy (an isenthalpic process). Such a process can be approximated in the real world by expanding a fluid from high pressure to low pressure across a valve. Under the right conditions, this can … Continue reading Joule-Thomson Effect

One of the challenges of using superconducting magnets is the connection of the magnet to a room temperature power supply. This is accomplished via current leads. The trick is that current leads should ideally have a low heat leak, since they connect room temperature to cryogenic temperature, while at the same time they should have … Continue reading Current Leads

Multilayer insulation (also referred to as superinsulation) is a key component in the reduction of heat leak to cryogenic systems due to thermal radiation. MLI consists of a series of uncooled reflective surfaces placed in the vacuum space between two surfaces, one warmer than the other. Generally speaking, for ideal systems the reduction in thermal … Continue reading Multilayer Insulation

Transfer lines may in some real sense be thought of as the cryogenic fluid analogy of current leads. While current leads carry electrical power to where it’s required in a cryogenic system, transfer lines do the same with cryogenic fluids. Transfer lines range in complexity from very simple U-tubes containing only one fluid line to … Continue reading Transfer Lines

Zero Boil Off cryostats are those that contain liquid cryogens but are designed to eliminate or vastly reduce the boil off of  the liquid. These cryostats combine some of the advantages of Cryogen-Free systems (e.g. ease of use and long operational lifetime) with the advantages associated with a reservoir of liquid cryogens. Such a reservoir can … Continue reading Zero Boiloff

Cryomodule is a term that is most commonly used to refer to cryostats that contain superconducting radio frequency (SRF) cavities. Such cavities are used to accelerate charged particle beams and are a major component of modern particle accelerators. Using the term cryomodule to refer to cryostats containing SRF cavities appears to stem from the original … Continue reading Cryomodule

Reaching temperatures below 1K requires different techniques than the various helium gas cycles found in large scale refrigeration plants and small cryocoolers. One of these techniques is Adiabatic Demagnetization Refrigeration (ADR). This technique takes advantage of the fact that the entropy of paramagnetic materials in a magnetic field is lower than when no field is present. … Continue reading Adiabatic Demagnetization Refrigeration

A cryogen is any fluid that operates at cryogenic temperatures (below roughly 150K – 120K). Using this definition, helium gas at 40K is a cryogen. Another more restrictive definition is to use cryogen to refer specifically to liquids at cryogenic temperatures. This is generally how it is used in the term cryogen-free. Thus, a cryogen-free … Continue reading Cryogen-Free

A cryostat is any device designed to maintain things (including fluids) at cryogenic temperatures. In general usage, cryostats tend to be passive devices rather than providing active cooling. In this usage, cryostats keep things cold by thermally isolating them from room temperature. This generally is accomplished by a combination of vacuum insulation, thermal radiation shields … Continue reading Cryostats and Cryocoolers

Helium II (He II) refers to the second liquid phase of the most abundant helium isotope (4He). Helium II is also referred to as superfluid helium. Helium II occurs once the temperature of the liquid helium drops below 2.17K. The phase transition between the first liquid phase of Helium (referred to as Helium I) and … Continue reading Helium II