NEW TYPES OF DILUTION REFRIGERATOR AND SPACE APPLICATIONS

Dilution refrigerators are now commercially available with a lowest temperature of the order of 5 mK. However, for special applications, special purpose refrigerators are needed. After a presentation of the different possible ways to cool down by dilution of He-3 in He-4, we discuss two designs that give more flexibility than the classical dilution refrigerators: (i) dilution refrigerators without 1 K pot; (ii) double still systems to allow a precooling by circulation of the mixture. In the second part, we compare the different possibilities to obtain low temperatures in space (T less-than-or-equal-to 100 mK). Finally, we describe the dilution in open cycles which is presently the only dilution refrigerator insensitive to gravity.