Cryostat

As a cryostat (Greek κρυος 'cold' ) a cooling device is called, can be reached by very low temperatures and kept constant. Find application cryostat inter alia, in the low-temperature physics, and superconducting technology for cooling of infrared detectors.

Cooling principle

A distinction bath cryostats, Verdampferkryostaten, dilution cryostat and Refrigeratorkryostaten.

In the bath cryostats the object to be cooled is surrounded by a cryogenic liquid. As a cryogenic liquid often used liquid nitrogen ( boiling point: -195.8 ° C / 77.4 K) or liquid helium ( boiling point: -268.93 ° C / 4.2 K).

Verdampferkryostaten the cooling is with cold gas, which is produced by vaporization and heating of a cryogenic fluid. This temperature can be set between just above the boiling point of the cryogenic liquid to room temperature in Verdampferkryostaten. Temperatures below the boiling point of the cryogenic liquid can be obtained (see vapor pressure) by reducing the pressure on the coolant and the associated reduction in the boiling point.

Dilution cryostat produce low temperatures in the millikelvin range. Here, the thermodynamic phase transition between a 3He - rich and 3He - poor phase is exploited in the 3He - 4He mixture cooling.

In Refrigeratorkryostaten cooling is provided by a small cooler ( cryocooler ) and thus without cryogenic liquid.

Construction

In order to cool the cryostat with little energy as possible, a very good thermal insulation is necessary. The supply of heat by convection is reduced by incorporating the cold components in an evacuated container. The attachment of the cold components on the warm outer container is done to reduce the heat conduction in as few positions with hangers and supports smaller thermal conductivity. The heat radiation is reduced by built in the evacuated space either active or passive cooled heat radiation shields. As a passive heat radiation shields are often about 10 - to 30 -fold stacked metallized plastic films, the so-called super insulation. In addition, the entire cooling system of the cryostat must be hundred per cent gas-tight, otherwise the entire collapsing process.

The shape of the cryostat is adapted to its particular task. For example, for measurements in the cryostat magnetic fields are adapted to the opening of the measuring cryostat and magnet for optical measurement are provided with windows for the measuring beam.

Application

Cryostat are used for examination or for the use of low-temperature phenomena: for example, for

  • Material investigation Microtome for cutting frozen preparations in the Histology and Biology
  • Photodetectors for mid- infrared
  • Image sensors for low-noise thermal imaging cameras
  • Magnetoencephalography
  • Magnetocardiography
  • Superconducting quantum computer
  • In medical magnetic resonance imaging ( MRI)
  • In basic research (magnets to 19 Tesla): synchrotrons, NMR spectroscopy, fusion reactors
Leak Digital Object Identifier
490018
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