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Cryogenic instruments in science

Cryogenic instruments are used in many areas of science. Operating an instrument at cryogenic temperatures increases the cost and complexity over room temperature operation, and a compelling reason is therefore required to do so. There are two main such reasons. The first is to increase the signal-to-noise of the detectors that are at the heart of many instruments. Many noise sources decrease as temperature is decreased, thermal noise being an obvious example. In addition to this, for some types of detector, the sensitivity increases as temperature is decreased, further increasing signal-to-noise. The second reason to employ cryogenics is so that superconductors can be used. Some detectors rely on superconductivity for operation, such as transition edge sensors and kinetic inductance detectors used in astronomy. Such detectors are often read out with superconducting electronics such as SQUIDS (superconducting quantum interference devices). Superconducting magnets are also used to generate the high magnetic fields required in applications such as particle physics and magnetic resonance imaging.

More information on some of the scientific fields using cryogenics is given below.


Cryogenic instrumentation has a long and continuing history in astronomy. The main drive to low temperatures is the need to increase signal-to-noise, both by reducing background noise from black-body radiation, and increasing detector signal-to-noise. As temperature is reduced, many sources of detector noise reduce, and for some detectors the sensitivity is also greatly increased. Needs range from temperatures of 150 and higher for the reduction of dark noise in CCD detectors, to temperatures below 100 mK for X-ray microcalorimeters. As instruments increase in complexity and size, new materials and techniques will be required to construct instruments to a reasonable cost and timescale. A further complication is that at some wavelengths it is desirable or even necessary to carry out observations in space. More information on the use of cryogenics in astronomy is given here.

Dark matter and fundamental physics

Some experiments to directly detect dark matter or rare events such as double beta decay require the measurement of extremely small temperature changes in large crystals. To achieve a useful sensitivity, the crystals have to be cooled to extremely low temperatures (as low as 10 mK). Cooling such large masses to such low temperatures is extremely challenging, particularly when coupled with the need to use radiopure materials and to use large volumes of lead shielding to reduce the background on the detectors from radiation.

Plans to use helium-3 as a direct detection medium for dark matter would involve operation at temperatures as low as 130 μK. While this is less than 10 mK below the operating temperature of the systems described above, achieving temperatures below 1 mK is extremely difficult. The difficulty of cooling a material depends on the ratio of initial to final temperatures; cooling from 100 mK to 100 μK is therefore comparable to cooling from room temperature to 100 mK.

Gravitational Wave Detection

The majority of work on gravitational wave detection is carried out using large laser interferometers (e.g. LIGO). A major noise source in such systems is thermal noise (Brownian motion) of the suspended mirrors in the interferometer. In current systems, the mirrors operate at room temperature, but moving to cryogenic temperatures has the potential to reduce this noise and thus increase sensitivity by orders of magnitude. Research towards the operation of such systems is underway, and an intereferometer in Japan, CLIO, has already started operation with cryogenic mirrors.

An alternative method of detecting gravitational waves employs large resonant masses. In order to operate with sufficiently low noise, these have to be operated at cryogenic temperatures, ideally temperatures well below 100 mK (for example Auriga, and Nautilus).

Magnet technology

Superconducting magnets are necessary in various research fields, including particle physics and nuclear magnetic resonance, and in medicine (magnetic resonance imaging). In the field of particle physics, upgrades to the LHC instrument at CERN will require a new generation of superconducting magnets to give higher fields and tolerate higher radiation environments and heat loads than has been the case until now.

Other areas

The advent of reasonably priced and reliable closed-cycle mechanical coolers is opening up many commercial applications for cryogenic instrumentation beyond traditional "niche" markets. New applications include spinoffs from astronomy in which detectors originally developed for astronomy are used in areas as diverse as X-ray detection for materials analysis in the semiconductor industry and THz (sub-mm) detection for airport security. The commercial development of cryogenic instruments will require reliable engineering data, and few companies have the facilities or the desire to carry out material property measurements in-house.

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Page created: Adam Woodcraft
Last edited 2008-4-25     Site map
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