What’s the difference between a cryocooler and a cryostat?
1 Comment
Dr. John Weisend II
February 16, 2009
Regarding cryostats and cryocoolers: 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 accomplished by a combination of vacuum insulation, thermal radiation shields and superinsulation to reduce radiation heat transfer, and low thermal conductivity connections between room temperature and cryogenic temperatures.
In order to get the items in the cryostat cold in the first place you have to use cryogenic fluids, such as liquid nitrogen or liquid helium or very cold nitrogen and helium gas or a cryocooler or cryogenic refrigerator (see below).
With this definition, pretty much anything you wish to keep cold will be placed inside a cryostat – the superconducting magnets in LHC or ITER are built into cryostats, the cold boxes of large helium refrigerators are cryostats, As you point out cryocoolers ( at least the cold parts of
them) are contained in cryostats.
The thermos bottle that you have at home is a rudimentary form of a cryostat – is has a insulating vacuum and silvered walls to reduce heat transfer between room temperature and whatever you put into it. It thus keeps cold things cold and hot things hot. The thermos bottle was invented by James Dewar to store cryogenic liquids during his efforts to liquefy hydrogen. A synonym for cryostat is dewar. Many people, myself included, tend to use dewar when referring to cryostats designed solely to store cryogenic liquids. But this is not universally true and one occasionally hears people referring to test dewars that contain experimental equipment.
Okay, so now what’s a cryocooler? Cryocooler comes from the phrase cryogenic cooler and is a device for providing active cooling of something down to cryogenic temperatures. There is a wide range of these devices ( pulse tube, Stirling, GM, Joule Thompson) that use different thermodynamic cycles and techniques to generate the cooling. There is a distinction in usage between cryocooler and cryogenic refrigerator.
Generally, the term cryocooler is used to describe smaller devices ( with a capacity of say 100 W or less) while cryogenic refrigerator (or cryoplant) is used to describe much larger systems like the CERN Helium refrigerators or even refrigerators with say 500 W capacity. There are exceptions to this usage, for example device that provide cooling using adiabatic demagnetization are almost always called Adiabatic Demagnetization Refrigerators (ADRs)rather than cryocoolers though they are generally quite small. While there are many types of cryocoolers; large cryogenic refrigerators all tend to use the same method to produce cooling (generally a version of the Claude cycle) as it is the best technical solution at these temperatures and scales.
1 Comment
Dr. John Weisend II
February 16, 2009Regarding cryostats and cryocoolers: 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 accomplished by a combination of vacuum insulation, thermal radiation shields and superinsulation to reduce radiation heat transfer, and low thermal conductivity connections between room temperature and cryogenic temperatures.
In order to get the items in the cryostat cold in the first place you have to use cryogenic fluids, such as liquid nitrogen or liquid helium or very cold nitrogen and helium gas or a cryocooler or cryogenic refrigerator (see below).
With this definition, pretty much anything you wish to keep cold will be placed inside a cryostat – the superconducting magnets in LHC or ITER are built into cryostats, the cold boxes of large helium refrigerators are cryostats, As you point out cryocoolers ( at least the cold parts of
them) are contained in cryostats.
The thermos bottle that you have at home is a rudimentary form of a cryostat – is has a insulating vacuum and silvered walls to reduce heat transfer between room temperature and whatever you put into it. It thus keeps cold things cold and hot things hot. The thermos bottle was invented by James Dewar to store cryogenic liquids during his efforts to liquefy hydrogen. A synonym for cryostat is dewar. Many people, myself included, tend to use dewar when referring to cryostats designed solely to store cryogenic liquids. But this is not universally true and one occasionally hears people referring to test dewars that contain experimental equipment.
Okay, so now what’s a cryocooler? Cryocooler comes from the phrase cryogenic cooler and is a device for providing active cooling of something down to cryogenic temperatures. There is a wide range of these devices ( pulse tube, Stirling, GM, Joule Thompson) that use different thermodynamic cycles and techniques to generate the cooling. There is a distinction in usage between cryocooler and cryogenic refrigerator.
Generally, the term cryocooler is used to describe smaller devices ( with a capacity of say 100 W or less) while cryogenic refrigerator (or cryoplant) is used to describe much larger systems like the CERN Helium refrigerators or even refrigerators with say 500 W capacity. There are exceptions to this usage, for example device that provide cooling using adiabatic demagnetization are almost always called Adiabatic Demagnetization Refrigerators (ADRs)rather than cryocoolers though they are generally quite small. While there are many types of cryocoolers; large cryogenic refrigerators all tend to use the same method to produce cooling (generally a version of the Claude cycle) as it is the best technical solution at these temperatures and scales.