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Sub-kelvin coolers
 
Adiabatic Demagnetisation Refrigerators (ADRs) have already been used onboard sounding rockets and scientific satellites such as Astro-E. They produce base temperatures of the order of 50 to 100 mK by reducing the entropy associated with the electronic spins of the atoms in paramagnetic salts.
 
Forcing the electronic spins to align in a single direction by means of a magnetic field of the order of a few tesla reduces the entropy. Cooling powers of about 10 µW are achieved.
 
ADRs offer very low base temperatures with simple operations and good duty cycle efficiency. The main challenges associated with ADRs are the need for large magnetic fields, implying large currents and potential EMI issues, and for high performance and high reliability thermal switches.
 
In Europe, Mullard Space Science Laboratory-MSSL (UK) is currently developing a dual stage ADR for XEUS. This ADR cooler will be capable of cooling detectors down to 50 mK.  
 
Dilution refrigerators, based on the quantum-mechanical properties of 3He - 4He mixtures, are routinely used on Earth to achieve temperatures below 100 mK, with cooling powers exceeding 100 µW. This technique is now being adapted for space applications and it has been qualified, under CNES funding, for use on the Planck mission.
 
 
Sorption Cooler
Sorption Cooler
3He sorption pump coolers offer interesting performances, due to their simplicity of operation, the lack of moving parts and the possibility for them to work in a closed cycle configuration with an efficient duty cycle (3He condensation phase versus hold time at base temperature). Typical cooling power is of order of 10 µW at 300 mK.

Sorption coolers have already flown on-board balloons (Boomerang, Maxima, Archeops), sounding rockets and on the satellite SFU (IRST-Infrared Telescope in Space instrument).

Based on this experience, CEA (F) developed, under ESA TRP funding, the 3He sorption cooler for the Herschel spacecraft. Two units operating at around 300 mK have been qualified for Herschel.
 
 
Last update: 2 May 2007
 


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