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Séminaire MCBT

Mardi 7 mai à 11h00,
Salle Louis Weil, E424,

Orateur : Angela Volpe (Institut Néel)
"A closed-cycle dilution refrigerator for space applications"


I will present the development of a gravity-insensitive 3He-4He dilution refrigerator to cool down detectors to temperatures below 100 mK aboard a satellite. First I will describe briefly the principles of dilution refrigeration. Then I will compare a conventional dilution refrigerator design, using gravity for its operations, with that of the Open-Cycle Dilution Refrigerator (OCDR), which has successfully delivered a cooling power of 0.2 µW at 100 mK on the Plank satellite for a lifetime of 2.5 years. This design, which works perfectly under zero-gravity conditions, has the disadvantage that the lifetime and the cooling power are limited, because the helium mixture produced in the cooling process is ejected into space. Our system overcomes these limitations by closing the cycle : the two helium isotopes are separated and circulated back into the dilution refrigerator to obtain continuous operations with a cooling power of 1 µW at a temperature of 51 mK (cooling requirements of future space missions). I will describe the separation\circulation system and I will show some results about the performances of our prototype, which meet future mission needs. Then I will discuss a crucial step to demonstrate the feasibility of using a closed-cycle dilution refrigerator in space : the confinement of the mixture liquid phase in the still in zero-gravity and under operating conditions. We have tested the liquid confinement in different porous materials under negative gravity and I will present the experimental results showing that they meet the operating conditions. Based on these tests a new still has been designed and it will be ready to be tested in about a month.

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